UNITED STATES OF AMERICA NATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. ********************************************************** IN THE MATTER OF THE INVESTIGATION OF * AMERICAN AIRLINES, INC., FLIGHT 1420, * Docket Number McDONNELL DOUGLAS MD-82, N215AA * SA-519 LITTLE ROCK, ARKANSAS, JUNE 1, 1999 * ********************************************************** Arkansas Excelsior Hotel Bill Clinton Ballroom Three Statehouse Plaza Little Rock, Arkansas 72201 Friday, January 28, 2000 8:30 a.m. Board of Inquiry HONORABLE JIM HALL, Chairman Board of Inquiry THOMAS HAUETER, Deputy Director Office of Aviation Safety JOHN CLARK, Deputy Director Office of Research and Engineering BARRY SWEEDLER, Director Office of Safety Recommendations and Accomplishments BEN BERMAN, Hearing Officer Office of Aviation Safety Technical Panel GREGORY SALOTTOLO GREGORY FEITH EVAN BYRNE MARK GEORGE CHARLES PEREIRA LAWRENCE ROMAN DAVID TEW DONALD EICK Public Information Officer PAUL SCHLAMM Office of Public Affairs Washington, D.C. Parties to the Hearing LYLE STREETER, Air Safety Investigator Accident Investigation Division, AAI-100 Federal Aviation Administration RONALD J. HINDERBERGER, Director Airplane Safety Boeing Commercial Airplane Group ROBERT W. BAKER, Vice Chairman American Airlines, Inc. CAPTAIN CHRIS D. ZWINGLE Special Assistant to Chairman National Safety and Training Committee Allied Pilots Association KATHY LORD-JONES National Safety Coordinator Association of Professional Flight Attendants ROBERT KUESSNER National Weather Service DEBORAH H. SCHWARTZ, A.A.E. Airport Manager Little Rock National Airport J.T. CANTRELL, Training Chief Little Rock Fire Department I N D E X WITNESS: PAGE: Aircraft Performance Thomas Yager, Senior Research Engineer 791 NASA Langley Interview by Charlie Pereira Thomas Melody, Chief Pilot, Flight Operations 895 and Cuthbert J. (C.J.) Turner 895 Engineer Project Specialist, Aerodynamics and Neal Gilleran, Manager, Landing Gear, Brakes 895 and Hydraulics Boeing Long Beach Interview by Charlie Pereira Airport and Aircraft Rescue and Fire Fighting Ben Castellano, Manager 1039 FAA Airport Safety and Certification Branch AAS-310 and Gary Skillicorn, Lead Systems Engineer for 1039 Navigation Interview by Gregory Feith Survival Factors Stephanie Manus 1129 Passenger on-Board AAL Flight 1420 Interview by Gregory Feith Airport and Aircraft Rescue and Fire Fighting Robert Cook, Contractor 1139 Engineered Arresting Systems (ESCO) Interview by Gregory Feith Larry Tyner, District Chief 1162 Little Rock Fire Department Interview by Gregory Feith P R O C E E D I N G S 8:30 a.m. CHAIRMAN HALL: We will reconvene this hearing of the National Transportation Safety Board. This is a public hearing in connection with the Accident Investigation of American Airlines Flight 1420, McDonnell Douglas MD-82, Serial N215AA. This accident occurred June 1, 1999, at Little Rock, Arkansas. Mr. Berman, would you please introduce our next witness? MR. BERMAN: I call Mr. Thomas Yager. Whereupon, THOMAS YAGER having been first duly affirmed, was called as a witness herein and was examined and testified as follows: INTERVIEW BY BOARD OF INQUIRY BY MR. BERMAN: Q Good morning, sir. A Good morning. Q Would you please state your full name and address for the record? A Thomas J. Yager. Mail Stop 494 -- 497, NASA Langley Research Center in Hampton, Virginia. Q And your employer is? A The National Aeronautics and Space Administration. Q Thanks. What is your position at the Langley Research Center? A I'm currently a senior research engineer. Q How long have you been in that position? A For the last 13 years. Q Could you tell us about your duties and your responsibilities in that position? A Yes. Currently, I'm program manager on a joint international effort to look at winter runway conditions, much like we have here today in Little Rock. This is a joint effort with the FAA, Transport Canada, NASA and several government agencies in Europe, where we're looking at airplane performance under these conditions. I've also conducted several studies of tire performance on a variety of pavement surfaces, both dry and wet, as well as snow and ice-covered, at our Langley Track Facility in Virginia. I've been involved in developing tire designs and pavements for use in the Space Shuttle Program. I've looked at anti- skid brake systems on a variety of airplanes, and since about 1970, I've been involved in approximately 30 aircraft accident investigations where loss of traction is a suspected cause. Q Okay. Thank you. And could you please tell us about your education and training and prior experience that led you to your current position? A Yes. I've got a Bachelor of Science Degree from the University of Portland in Engineering Science, and upon graduation there in 1963, I accepted a position at NASA Langley, and I've been essentially working in that same division for the last 37 years, looking at aircraft ground-handling performance. Q Very good. And do you have any FAA airman certificates or other licenses that you can tell us about? A No, I do not. Q Okay. Thank you very much, sir. MR. BERMAN: Mr. Pereira, go ahead. MR. PEREIRA: Thank you. INTERVIEW BY THE TECHNICAL PANEL BY MR. PEREIRA: Q Mr. Yager, what resources and facilities does NASA have at its disposal to investigate airplane braking, landing performance, runway characteristics, etc.? A We have several at NASA Langley that I'm directly involved in. I guess I should identify those. One of them is depicted in the first chart. It's our Aircraft Landing Dynamics Facility. If you could bring that up on the screen? This facility is unique. It's one-of-a-kind in the world. We have a large tubular steel test carriage, weighs about a 110,000 pounds, to which we can attach a variety of aircraft landing gear systems. The next chart or overhead shows that carriage during propulsion, and this is a view of the test track. It's 2,600 feet in length. We use a waterjet propulsion system that produces two million pounds of thrust on this carriage. We get it up to a top speed of 220 knots in 400 feet, and then we coast through an 1,800-foot test section where we do free rolling, braking and cornering tests of a variety of landing gear systems. We can look at different pavement treatments, different wetness conditions, including ice, with this facility. We've got three other major facilities. I think there's one other view of this Aircraft Landing Dynamics Facility. Normally, we can make four runs a day with this. It takes about an hour to pump the water back up. We use 11,000 gallons of water. Each test runs -- though it's quite economical in terms of water and electricity. It's only $50 a test run. So, the aviation community has taken advantage of it, and we've done several studies in support of Boeing and other air frame manufacturers and tire manufacturers as well as brake system designs. The other three facilities that are not depicted here in charts that we have available is an Instrument and Tire Test Vehicle. It's a large truck with an instrument fixture on the back that we can perform braking, cornering and fix-slip test modes with, and that can accommodate commuter-type aircraft tires as well as vehicle tires. We have what we call a Diagonal Brake Vehicle that's been used in several runway friction evaluations in support of accident investigations, and that vehicle is still in use, and it supported the Space Shuttle efforts, both out at Edwards Air Force Base and down at Kennedy Space Center. The fourth vehicle or test facility that we have at Langley is relatively new. It's an Instrument 747 Airplane that we used last February in some braking tests up in Northern Michigan, and we hope to use it much more in the future years, looking at not only ground-handling performance but several of the problems related to in-flight performance. One of the studies that's underway now is to implement a better weather avionics package that pilots can use in the cockpit as they're flying from Point A to Point B, and I know that's of concern in this accident event. Q Okay. I understand you have a presentation on airplane braking performance and other subjects of interest to this investigation. So, if you'd proceed with that, please. A Very good. Thank you, Charlie. If I could have the first slide, which is an overview of the factors affecting aircraft wet runway performance. I apologize for the size of the type, but I'll try and go through it one block at a time. Basically, we have four -- four factors identified here on the left, atmospheric, runway surface, aircraft tire and runway surface again. These first two go into determining the runway water depth that's on the surface. We must consider the rainfall rate and the wind velocity and direction. We've got to consider the slope of the runway, both from a transverse and longitudinal direction, and then what we call the macro texture of the sandpaper-type finish on the surface. These factors here influence the water depth. In terms of the tire-pavement drainage capability, ground speed plays an important role in tire friction performance on a wet runway. Many of you are aware of the problem with hydroplaning. When you can get up to high enough speeds to develop that, that becomes a definite problem. One of the main factors influencing hydro-planing is inflation pressure, tread design and wear. We found in tests at Langley that these are important factors to consider in terms of tire- pavement drainage capability, and then the runway itself contributes to that in terms of both micro texture and macro texture. Having defined these two blocks, we can then go into determining the available tire-pavement friction coefficient that is influenced by both the aircraft parameters as well as the pilot inputs, his technique or her technique applying brakes and using directional control. In terms of the aircraft, we have to deal with aerodynamics, engine thrust, brake systems and, of course, the landing gear geometry itself. All of these factors combine to come up with the eventual aircraft wet runway performance, and to date, I've been involved in studies of 13 different types of airplanes and looking at these parameters in general, and one of those types has been the DC-9 and later the MD-80. If I could go to the next chart, -- MR. CLARK: Would you describe the difference between micro-structure and macro-structure? THE WITNESS: Right. Macro texture is the large roughness in the surface that is visible to the eye. Micro texture is a small sandpaper type of texture that you can only feel, and I've got a chart later in the presentation that better describes the difference between macro texture and micro texture. These two terms are not related to runway roughness. Roughness is more of a long wave form phenomena and not connected with macro texture or micro texture. This chart here basically gives the forces and moments that are developed between the tire and the wet pavement. First of all, you've got the direction of motion left to right, the tires spinning in this direction. You have a rotational acceleration this way. You have brake torque with the braking going on. This FW force is a combined rolling resistance, and if you have fluid on the runway, drag produced by that fluid. Now, if you raise the chart just a little bit, you can see at the bottom here that during normal operations, the -- the vertical load on the tire is not centered directly below the axle. It's somewhat aft of it. This W being the weight on the landing gear, and the L being the lift factor, and that lift factor, of course, is influenced by the configuration of the airplane. Having spoilers on, that lift factor is low. Not having spoilers on, the lift factor is quite high, and these two terms here go into the equation along with friction coefficient to develop the added drag force that the pilot can accomplish during braking. Now, as speed goes up, this vertical force developed between the tire and the pavement starts to move forward, and when you get up to hydroplaning speeds, it will be ahead of the axle and cause a spin-down moment, and if conditions on the pavement persist, that spin-down moment can result in the wheel stopping and not rotating and yet the vehicle is going at over a hundred knows velocity. We've seen this in -- in films of our -- at our test track facility. CHAIRMAN HALL: Mr. Yager, could I ask you if the -- if the -- what happens to that equation if the vehicle is sliding sideways? THE WITNESS: That compromises the -- the situation in that with steering inputs, you take away from the drag force. The higher the steer angle or the yaw angle, the lower the drag force is that you can develop between the tire and the pavement. It's a vector phenomena, and if you have a hundred pounds being able to be developed between the tire and the pavement, and steering requires 70 pounds, we only have 30 pounds left for braking. This next chart shows the variation of friction coefficient developed between the tire and the pavement with what we call slip ratio. Now, slip ratio of zero is basically free-rolling. There's no apparent slip between the tire and the pavement. A slip ratio of one equates to a locked wheel condition. There is a total lock of the wheel, and you have a hundred percent slip rotation. Anywhere in between there is considered relative slip of 20 percent versus the forward speed of the vehicle. In this area here, we consider this the front part of the new slip curve, and it's in this area here where most of the antiskid brake systems try and operate, and they try and maintain brake pressure so that the tire is developing near the new max value in this chart here. Now, as conditions change, this new max value, .8, under wet conditions, might go down to as low as .4 and might move further out on the slip ratio curve, and I've got some later charts that will describe that development. The -- normally, the rolling resistance of the tire between the pavement is nominally .02, a relatively low value, although this is taken into account in our equations of motion in determining the aircraft braking distance values. This next chart basically goes through a classification of different types of runway surfaces that one might encounter, other than today. You've got dry surface or there's no moisture, standing water, present. Damp is basically less than a hundredth of an inch, and as such, if you put your hand down on the surface, you can feel the moisture. Under wet conditions, which were part of the -- the events of June 1st, we have standing water on the surface to a depth between a hundredth of an inch and a tenth of an inch. Excuse me. Under flooded conditions, we consider standing water on the surface that exceeds a tenth of an inch, and this can happen under moderate rainfall rates, and with those definitions in mind, I'll be showing you several charts that describe wet runway performance as well as flooded runway performance. This is basically a chart showing two types of hydroplaning, and this is the dynamic hydroplaning, and then a third type of friction loss on a wet surface, what we call reverted rubber skidding, and the schematics here depict each one in terms of what's happening with the tire/pavement combination. The contributing factors for -- excuse me -- wet -- for viscous hydroplaning must include a damp or wet pavement, medium to high speed, poor pavement texture and worn tire tread. The alleviating factors, if you have good micro-texture, if you have pavement grooving or if you have a good tread design, viscous hydroplaning would not occur, and another indication of viscous hydroplaning is a poor performance of the antiskid brake system. Under dynamic hydroplaning conditions, you need a flooded pavement, one that has at least a tenth of an inch of water on it. You need high speed. In terms of the airplane inflation pressures for Flight 1420, the -- the critical hydroplaning speed was a 126 knots for spin down. For spin up, it was a 107 knots. Low tire pressure would be a contributing factor, and worn tire tread would be a contributing factor to dynamic hydroplaning. Good macro texture, grooving, high tire pressure and good tread design would alleviate this from occurring, and we had good tread design on the tires of Flight 1420 as well as high tire pressure. Concerning reverted rubber skidding, the third principle cause of wet pavement friction, that normally occurs on the wet or flooded pavement. High speed is required. It can persist down to low speed. Poor pavement texture is also required. Sometimes a deficient brake system can cause reverted rubber skidding, causing the tire to lock up. To alleviate this from occurring, you need good pavement texture, grooving or improved antiskid control devices. We could go on to the next slide. The critical dynamic hydroplaning speeds for a non-rotating wheel, which is the case you have during the landing, the spin-up hydroplaning velocity is 7.7 times the square root of the inflation pressure. With the 195 knots that we had -- 195 psi that we had in the American Airlines MD-80 airplane, that equated to a 107 knots. For a rotating wheel, one that has spun up and is now going into a flooded portion of the pavement, the spin-down hydroplaning velocity is nine times the square root of inflation pressure, and this is the equation that most people are familiar with, but it results in a higher speed. For the accident airplane, it would be a 126 knots, and in terms of miles per hour, that equates to about a 145 miles per hour. This chart here shows the effect of transverse grooving, which the Little Rock Runway 4 Right has, on the critical hydroplaning water depth. I've plotted the minimum water depth required between the tire and the runway on the system, and on the X axis, the water depth that actually occurs is required on the runway. For an ungrooved runway, you don't need as much water as what you do for a grooved runway. Now, the grooved runway in this example was three-eighths by three-eighths in width and depth and on two-inch centers, which is similar to what we have at Little Rock. Little Rock is two-inch centers, quarter-inch wide, three- eighths -- three-sixteenths of an inch in depth. Now, if you take those dimensions and put it into this chart here, the water depth required or the water depth developed on the runway that would produce a dynamic hydroplaning effect would be approximately .28 inches in depth. This chart is somewhat busy, but it basically shows a comparison of the airplane braking performance between the 737 and the 727 airplane, and these values were obtained at two different test sites, one at Wallops Flight Facility in Virginia and the other at the Brunswick Naval Air Station up in Maine, where we did some snow and ice tests back in the mid '80s, and I'm showing the variation of the effective friction coefficient which is the total braking effort developed by the airplane with the four main gear tires on each airplane. First is ground speed, and in the case of the 737, the hydroplaning speed was a 105 knots. In the case of the 727, the hydroplaning speed was a 112 knots, and I show, first of all, at the top the dry braking performance on both grooved and non-grooved runways for the 737 and the 727 airplane. You see the dotted line almost directly below the dry surface is truck wetting on a -- on a grooved surface at Wallops. Now, the grooved surface at Wallops was one-inch spacing, quarter- inch wide, quarter-inch deep, and through this range from approximately 10 knots to a hundred knots, we almost saw no difference between the wet braking performance on the grooved surface versus the dry for the 737 and also for the 727 airplane. But when we go to a non-grooved surface, we get a decrease in effective friction coefficient, less of a decrease for the 727 than we do for the 737, and there's much more of a velocity effective friction co-efficient developed between the tires and the pavement. We go into snow-covered and flooded runways, we get even further reduction in -- in effective friction coefficient, and under glare ice conditions at Brunswick Naval Air Station, we were down in the -- almost the rolling resistance range of the -- of the airplane. I know in talking to the pilots after making these runs on the ice-covered surface at Brunswick, they had the sensation -- it was a 2,000 foot ice section, and on either side, it was bare and dry, and when they entered the test section in the case of the 737 airplane at about 82 knots, the pilots told me the sensation was one of speeding up when they applied the brakes rather than slowing down, and they actually came out of the 2,000 foot test section doing 62 knots. So, we had to do several more runs in order to complete this velocity curve. MR. CLARK: Mr. Yager, why is there so much difference between a 727 and a 737? THE WITNESS: One thing is the antiskid brake system, and the second item is the tire inflation pressure. The 727 had a higher hydroplaning speed than the 737. MR. CLARK: Okay. And do we have -- do you have that kind of data for the MD-80, where we can -- is that -- THE WITNESS: Well, I've got data for the MD-80 tires. I don't have it for the MD-80 airplane itself. I've got data for a DC-9 that we tested in early -- early 1980s with the FAA. It was a DC-9 out of Oklahoma City, and there's a NASA report documenting those tests, and they included wet runway tests on -- yeah -- on six different runways, and that can be given to the Board. MR. CLARK: Okay. We'll do that. THE WITNESS: Okay. This next chart shows the wet runway effects on tire aircraft braking traction, also. In this case, the airplane was a C-141 that we were operating with the Air Force, and the chart on the left not only shows the variation of runway friction coefficient with ground speed up to a 140 knots under dry conditions for grooved surface and for non-grooved surface, but also shows the effect of tread design. A five-grooved tire with nominally a grooved depth of two-tenths of an inch versus a smooth tire that doesn't have circumferential grooves, you do get an appreciable difference in the friction coefficient developed. Now, this ATD value here of -- indicates the average texture depth, and similar measurements were taken at the Runway 4 Right here at Little Rock, and with the grooving, our average texture depth was .055 in the clean concrete area in the middle of the runway. As you can see, with the one-inch spacing, quarter-inch width, quarter-inch depth, you get a somewhat higher average texture depth of .067. Now, in terms of antiskid efficiency, basically what we're plotting here is the efficiency versus the runway traction coefficient. Again, this is related to the effect of friction coefficient, and there's two things here. One, as the speed increases, the efficiency goes down somewhat, and as the friction level between the tire and the pavement goes down, so does the efficiency level of the antiskid system. That's one of the dilemmas that the antiskid manufacturers face in that they've got to accommodate a high- friction dry surface, and at the same time have the system capable of accommodating a low-friction icy surface, and in many instances, that's hard to -- to reach an adequate compromise. This chart here depicts pavement surface characteristics, and I alluded to it earlier when I was talking about the difference between micro texture and macro texture. The first surface here is smooth like a billiard surface. You don't have any micro or macro texture. Under damp conditions, the ability to alleviate low friction or slipperiness is poor in both damp and flooded conditions. As you go up in micro texture and macro texture, you get better and better ability to alleviate damp conditions and flooded conditions, to the point where the last two surfaces, transverse grooves and the porous friction course, some people refer to it as popcorn mix, you get excellent damp conditions, alleviation of slipperiness and also under flooded conditions, very good drainage, and that's the name of the game with the grooves and the porous friction course, is to minimize the amount of water that can be collected between the tire and the pavement as the tire passes over it during the landing or take-off roll. BY MR. PEREIRA: Q Mr. Yager, could you go back to that slide and point out which one of those would be similar to the Little Rock runway? A Sure. It would be this one right here, similar to the Little Rock runway. The micro texture was above average, and the grooving was satisfactory. Q Okay. And could you have them zoom in on the grooved image for that one, just to show the -- A Micro -- Q -- micro texture on the top surface there? A And basically we're talking about the -- the sandpaper texture between the grooves, and this is something you can feel as opposed to actually see. The porous friction course is basically that. It allows water to drain vertically down to a subgrade that is non-porous, and then the water drains out to the side from there. Okay. Move on to the next one. This is an attempt to show the effects of this surface texture and speed on the ability of a tire to develop friction coefficient on a wet pavement. MR. CLARK: Mr. Yager, before you get to that, would you describe the -- kind of the -- the real-world effect of what friction coefficient means, such as the friction coefficient of .5? THE WITNESS: Right. A friction coefficient of .5 in terms of airplane braking performance is exceptionally high. You would only get that under low speed dry pavement conditions. MR. CLARK: Okay. What I was referring to was if I had a friction coefficient of .5 or .4, what -- what does that -- what would I feel in the airplane? THE WITNESS: Oh, okay. If that was the only thing slowing you down, you didn't have reverse thrust, aerodynamic drag, rolling resistance, you'd probably feel approximately .3 gs on your body in deceleration level. MR. CLARK: If the friction coefficient was .5? THE WITNESS: .4 or .5, right. MR. CLARK: And field .3? THE WITNESS: Yeah. MR. CLARK: A third of a g-d cell? THE WITNESS: Right. MR. CLARK: Okay. THE WITNESS: Right. MR. CLARK: All right. THE WITNESS: Okay. Getting back to this chart, there's actually four different surfaces depicted here, and we go through a speed range of 25 to a hundred knots. Of course, at the low speed, we get our highest friction values, and at the higher speeds, since the surface is wet, and we're operating a smooth tire that has an inflation pressure of a 140 psi, we -- as we go up in speed, we decrease the average friction coefficient because the smooth tire cannot handle the water being introduced into the front of the footprint, and as we go up in texture depth, though, this accommodates less water -- as the texture depth goes up, there's less water influencing the tire footprint contact area, and, so, with higher texture depth, we get higher friction values, basically, and again as I mentioned for the Little Rock airplane accident, Runway 4 Right had a .055 average friction texture depth value. So, it's way out here in terms of this plot here. The rubber-contaminated surfaces at either end of the runway produced on the average of a .047 value on Runway 4 Right. MR. CLARK: The chart you have shows 140 psi, and I thought you mentioned earlier the MD-80 tire pressure was 195? THE WITNESS: That's correct. It had a higher tire pressure. MR. CLARK: How would that affect -- can we get a chart generated that would reflect that tire pressure? THE WITNESS: Yes, I could. Based on -- MR. CLARK: Generally, how would that affect this graph, if we were to use 195? THE WITNESS: Well, I can give you a quick relationship. The hydroplaning speed for a tire inflated to a 140 psi would be a 106 knots, whereas a 195 psi, the value's a 126 knots. So, you could expect approximately a 15 to 20 percent improvement with the tires on the MD-82 versus this particular tire. The other factor that you've got to dial in, though, in terms of how well the tire can develop friction forces is the tread design, and the particular chart that I just showed was with a smooth tire, and with the treaded tires that we had on the MD-82, I suspect that the friction coefficient based on the average tread groove depth there, it would increase the values another 15 to 20 percent. So, we'd probably see an overall improvement of 40 percent versus the values that were on that chart. MR. CLARK: Okay. THE WITNESS: It would be higher. MR. CLARK: Yeah. I think if it's possible, we'd need to develop those specific curves to the specific -- THE WITNESS: Okay. MR. CLARK: All right. THE WITNESS: Moving on to the next one, this shows a large number of runways that I've measured personally myself, both here in the United States as well as in Canada and over in Europe, and I've divided the runways up into five different types, starting with A, going down through E. A being the non-grooved low micro texture/low macro texture surfaces, and then as you increase maximum micro texture, you proceed on down to the Type E, which is deep grooved surfaces and open texture surfaces, and the scale here at the bottom is logarithmic, and going with that scale, our Runway 4 Right at Little Rock is in this area here. It's definitely a Type E excellent macro texture surface, and the drainage measurements that we took in November indicate the cross slope is also very uniform and provides good drainage of the water from the center line down to the shoulder. The next chart shows another effect, I believe, of -- of how texture influences tire friction performance. Okay. This is how texture influences the amount of rainfall that a given pavement can handle during a rainfall event. What I've plotted here is the rainfall rate in this case in millimeters per hour, over here inches per hour, versus the pavement macro texture depth at the bottom, and then I've got curves for each transverse or cross slope that's normally found on different runways around the world, starting at a quarter percent slope and going up to two percent slope or crown on the runway. Now, we took transverse slope measurements at Little Rock, and we determined the average slope to be 1.42 percent or very close to the 1.5 percent that's on the Little Rock Airport layout, and using this 1.5 percent, if you come into this plot at the .055 value that we measured in terms of texture, go up to 1.5 and then across, you can find that that surface, 15 feet from the runway center line, can accommodate about a 1.6 inch per hour rainfall rate. If the surface had been grooved to, say, a one and a half inch spacing rather than two inch, and it was a quarter inch wide/quarter inch deep, which is the current FAA advisory circular recommendation, the value would have moved up to 0.62, and with the same slope, we'd be close to a two inch per hour rainfall rate that that runway could accommodate. As most of you are aware from the testimony yesterday and the day before, the Flight 1420 touched down just slightly right of center line, 5,200 feet from the end of Runway 4 Right, and in that area, due to the crosswind coming from left to right, there would be less than a tenth of an inch of water in that area of the runway, and under those conditions, and with the high vertical sink speed that he touched down at, I have no problem or no question about the wheels spinning up on touch down. This equation here is somewhat conservative. Since we established these curves for the five different cross slopes, we found in later measurements that there might be a need to adjust these curves upward, and in fact as much as 20 percent on some readings that we got at the Kennedy Space Shuttle Landing Facility in Florida, and I'm working on coming up with some new curves here, and with these new curves, the .055 value might allow us to get better -- to accommodate more than two inches per hour rainfall rate. This curve again shows the influence of tread depth on tire friction performance. Again, it's friction coefficient versus ground speed, and we've got a five-grooved ribbed tire. The water depth is three-tenths of an inch. The inflation pressure's a 150 psi. The hydroplaning speed in this case is a 110 knots. With the ribbed tread tire, you can develop over .4 friction coefficient. With the smooth tread tire, you're down to .3 and rapidly decreasing with increasing speed. Speed plays a major role in wet pavement performance, but under snow and ice conditions, it's not as dominant a factor. It turns out that even at low speed on an ice surface, you can develop -- you can develop friction coefficients of less than .1. This chart here shows the influence of ground speed on braking distance of -- in this case, it was a Conveyor 880 airplane, and we were looking at both smooth and grooved concrete surfaces, full antiskid braking, and the solid line on the left here depicts the dry stopping distance with brakes applied at a 130 knots, and we get about 1,700 feet of stopping -- total stopping distance. This was on both a -- this was on a smooth surface, a non-grooved surface. If you go out here to the dashed line, this is on a wet smooth surface, one that had a hundredth of an inch water depth, and the stopping distance goes up to 2,800 feet. On a slush-covered runway, half-inch deep, the tires were hydroplaning, and it was a smooth surface. We almost tripled the stopping distance going out to 4,400 feet. On a wet grooved surface, however, these grooves, by the way, were one inch spacing, quarter inch wind, quarter inch deep, we almost get the same stopping distance as we get on dry, 1,800 feet versus 1,700 feet, for this Conveyor 880 airplane, and again the inflation pressure was a 150 psi. In analyzing different aircraft antiskid braking systems, these are some of the major players in, first of all, when you can expect normal behavior, and, secondly, when you can expect abnormal antiskid operation, and when high wheel spin-up accelerations occur on a medium -- on a high to medium runway traction surface, early spoiler deployment at touch down, you can expect normal antiskid operation. Now, in the accident event, we did not have early spoiler deployment, and hence we can expect abnormal antiskid operation, and in certain instances, when the airplane touches down on a flooded surface, you don't get wheel spin-up, and when that occurs, pilot brake application before wheel spin-up gives the antiskid system a false velocity reference, and it won't be as efficient as it would be if the wheels were fully spun up synchronous to the ground speed of the airplane. Typical antiskid operation anomalies include loss of touch down protection, what we call brake wheel ratcheting, which is a high cycling of the brake pressure causing fore and aft motion of the landing gear and then loss of locked wheel protection, and these three anomalies equate to a loss or lack of adequate ground speed reference. The current black boxes that control antiskid operation, most of them are tied into a wheel velocity or a wheel slip speed for the braking wheel. This is one of the anomalies alluded to in the earlier chart. Loss of locked wheel protection. Normally, when you're coming in for a landing, you do not want the wheels locked due to brake pressure, and, so, most systems on present-day airplanes have this protection. But under braking conditions -- what I show here is the braking traction coefficient variation with the ground speed, and one can expect on a wet runway -- wet runway condition, the maximum level of braking that you can develop is depicted by this solid curve, whereas the minimum level is depicted by this dashed curve, and with normal antiskid operation, you should be able to develop friction coefficients within this band width as speed varies from, say, a 110 knots down to your taxi speed. But when the airplane touches down, and the wheels do not spin up or you get into what we call reverted rubber skidding, which I discussed earlier, the coefficients stay low for the entire run- out of the airplane on the runway, and in some cases, it will run out of runway length before he comes to a stop at this low braking friction coefficient. The -- the other factor that enters into, of course, the braking equation is the effectiveness of reverse thrust, and that helps out quite a bit on low friction surfaces in stopping the airplane before the end of the runway. This last chart shows an effect of both braking and steering on the forces developed between the tire and the wet pavement. At the top, I show braking friction coefficient versus slip ratio. Again, zero slip ratio is free-rolling, one is locked wheel, and at the bottom, the variation of cornering friction coefficient with slip ratio. The dilemma with antiskid control systems is that to preserve braking, the antiskid must operate at increasing slip ratios as the airplane yaws. At zero degrees yaw, we can get maximum or peak braking at a relatively low value of slip, but as the yaw increases, this maximum value of braking occurs at a higher slip, and the magnitude of it is reduced, due to the fact that some of the forces developed between the tire or a component of the force developed between the tire and the pavement has to go into steering, and to preserve cornering, the antiskid must operate at low slip ratios. As you go up in slip ratio, the cornering capability of the tire decreases, and in terms of just four degrees, it can reach zero at about 50 percent slip. At 16 degrees yaw, it would reach zero at a locked wheel condition. Of course, if you've got a locked wheel condition, you're not going to be developing any cornering coefficient under wet runway conditions. It's this type of behavior that was obviously present in the landing at Little Rock. As the video depicted on Wednesday, he was drifting right shortly after touch down. He was able to recover from that right drift, went across the runway and then went into another yaw angle attitude with both main gears off of the runway and then went off the end of the runway under a combined yaw angle of the airplane with -- with braking. That basically concludes my presentation on tire/pavement wet friction performance. MR. PEREIRA: Thank you, Mr. Yager. BY MR. PEREIRA: Q On the slide where you discussed the various friction levels for the different speeds, and we talked about tire grooves improving that performance on wet runways, what effect would the yaw angle have on the ability of the tire grooves to penetrate the water? A As you increase yaw angle, the frontal area of the tread grooves diminishes due to that yaw angle, and hence their ability to relieve the water from between the tire/pavement -- tire tread and the pavement would be diminished. But going up to as high as 20 degrees yaw angle, that deterioration would be in the order of about 10 to 12 percent, if you just look at the geometry of the tread and those particular yaw angles. Q Okay. Thank you. You mentioned the surface texture of the accident runway was among the best in the United States. How does the runway compare with others in the United States with respect to all parameters of concern, such as measured wet friction, crown, overall water drainage capabilities, and its general ability to prevent hydroplaning and other braking problems? A There are several factors involved here, not the least of which is texture and cross slope. We found in our measurements back in November that were taken every 500 foot increment down the runway that the cross slope is -- is very uniform. It -- it provided drainage numbers of water going from the center line to the shoulder that were quite reasonable and not lengthy until you got to the portion of the runway that was non-grooved, which was the last 13 feet before the edge of the runway, where it slowed down somewhat. But compared to other runways where I've measured similar type drainage characteristics, it's equal to or better than some of these. It's not equal to the shuttle runway in Florida, but it's equal to several other runways that I've looked at. Secondly, in terms of friction, we had what we call a surface friction tester come up from Dallas-Fort Worth a couple days after the accident, and he took measurements with that device at both 40 and 60 miles per hour, and the numbers from those -- those tests -- which he did, by the way, made a run on the left side of center line and then made a second run on the right side of center line, approximately 10 feet off of center line, which is in the neighborhood of where the main gear would be if the airplane stayed on center line. At 40 miles an hour, he averaged .68 friction coefficient. At 60 miles an hour, he averaged .56 friction coefficient. The drop from 40 to 60 was nominal. I've seen non-grooved runways go from a 60 to 70 reading at 40 miles an hour down to as low as 20 at 60 miles per hour. So, the drop here was not that great, and it's attributed to the fact of the high macro texture on the grooved surface that we have at Runway 4 Right in Little Rock. The -- the tester, by the way, provides what's called a self-wetting feature, where it puts down 400ths of an inch of water ahead of the test tire, and the tire itself is operated at 12 percent slip or near the peak of this new slip curve that I showed earlier, and it's a fairly -- it's a very reliable device. It's been in operation now for nearly 15 years, and approximately 45 different runways around the world use this particular device for monitoring runway friction performance. Q Okay. So, in terms of its -- again, in terms of its general ability to prevent hydroplaning and other braking problems, would you say it's good or bad? A I would say it was excellent. Q Okay. Is there a Federal Aviation Regulation or advisory circular that specifies what Runway 4 Right's measured friction should be, and how does Runway 4 Right's measured friction compare to other runways? Actually, I think you just mentioned that, but -- A Oh, okay. We got a picture of the solid friction tester that was used in the test back in June, and the test tire here is driven off the rear axle of this vehicle, and this is one of the vehicles we use in our winter runway friction program. Getting back to your question, I have a chart here of the current FAA Advisory Circular 150/5320-12C, which is dated March 18th, 1997, and it shows seven different friction testing devices and what their friction levels should be for three different runway conditions. If I'm not mistaken, the runway at Little Rock was constructed in the late '80s, and there was another advisory circular in existence at that time, which only had four of these ground vehicle devices listed. Here, we have the KG Law runway friction tester, which is a minivan device. The skidometer, which is a trailer device. The airport surface friction tester, and the airport technology safeguard friction tester are basically both Saab vehicles, similar to the picture that was just shown. The grip tester device is from Scotland. It's a trailer device. The tetra is from Czechoslovakia. It's a car equipped with the fifth wheel that measures friction, and then the norse meter runner is a single-wheel trailer device, and at 40 miles per hour, and at 60 miles per hour, the minimum friction levels are indicated in the chart. Minimum under the self-wetting conditions are listed first, and then for maintenance and planning, you want to have at least this level, and for new design or construction, you want to have this level here. Now, with the runway at Little Rock, testing with the surface friction tester, like I say, at 40 miles an hour, we got .67, and at 60 miles an hour, we got .56. So, -- excuse me. At 40 miles an hour, we got .68 with the Saab friction tester, and .57 -- .56 with -- at 60 miles per hour. So, this does meet the current FAA advisory circular requirements. Q Okay. And in terms of that advisory circular, what you're saying there is that somewhere between the maintenance planning and the new construction -- A That's correct. Q Okay. A Right. Q Okay. A A lot of runways use these ground vehicle devices to determine when they should remove rubber deposits on the end of runways. Q Okay. And is it mandatory that airports monitor these values and adhere to those criteria in terms of planning for maintenance once it reaches those levels? A Right now, it's just a recommendation by the FAA. There's no mandatory requirement for any airport to perform these friction measurements. Q And do you think it should be mandatory? A Yes, I do, because the accuracy and the fidelity of the equipment has improved to the extent that they are quite good in determining the friction levels. Q Thank you. CHAIRMAN HALL: How much does it cost? You have to buy one of those things or you rent them for a test? THE WITNESS: You can go both -- both directions. The KG Law runway friction tester, I know, performs surveys for a variety of airplanes and is under a contract agreement. To buy one, they can run as much as a 150,000 per unit. The lowest-priced one is in the neighborhood of $30,000. CHAIRMAN HALL: And how often are -- should you take that rubber off the runway on a normal airport? THE WITNESS: Right. On a normal airport, once a year, usually in the Fall. The FAA has guidelines in this same advisory circular that based on traffic volume, you should remove the -- the rubber on a regular basis. Now, some of the high-volume airports, such as Chicago, JFK and Atlanta, they can be removing rubber every two or three months. BY MR. PEREIRA: Q And are those rubber removal -- are they requirements or are they just recommendations? A Again, they're just recommendations. Q Do you think that should be mandated, also? A Well, it's certainly would enhance the friction capability between the tire and the pavement, not having that rubber filling in the voids and reducing the macro texture. Q Thank you. Can you again summarize the condition of the accident airplane's tires with respect to the inflation pressure, the tread design, the tread wear, and how do you think their condition would have affected the braking performance of the airplane? A In general, their tread groove depths were better than average. They were in the neighborhood of 30 to 40 percent worn. Now, inspecting them at the accident site, three out of the four main gear tires were cut or abraded to the point where they no longer were inflated. There was only one tire still inflated to a 195 psi. In observing the tread condition around the circumference, I -- I saw no evidence of tread reversion or reverted rubber skid patches. The tread depth itself was in the order -- on all four main gear tires was in the order of .2 to .25 inches in depth. They were four grooved circumferential tread design with a wide center rib which is typical of transport airplane tread designs. They were bias ply tires. They were not radial belted tires, such as some of the newer equipment is using. From the standpoint of what I observed on the accident airplane tires at the -- at the scene back in June, they should have developed high to excellent friction on a -- on a wet runway because of their tread condition. Q Okay. And you mentioned bias ply versus radials. Would the radials offer any better wet braking performance than the bias? A No. Our tests have shown that radial tires, such as some of the 777 equipment flies, from a braking standpoint, they're comparable to bias ply tire. What you gain with radial tires is somewhat better cornering capability and somewhat better wear performance. You get about 20 percent more landings with a radial tire than you do with a bias ply tire, and again that's due to stiffness. Q And would that better cornering apply to wet and dry or just dry on the radial? A It would apply to actually both dry and wet for a radial tire. Q Okay. Thank you. Would you please explain the characteristics of the tire marks we found on the runway, and why we didn't find black rubber tire marks? A Right. Obviously the pavement surface is wet, and being wet, there were no black marks evident. The marks that I observed on that runway were basically scrub marks due to the high pressure between the tire footprint and the wet pavement. If -- under those conditions, we got this lighter appearance surface in the tire tracks versus the surrounding concrete area that was somewhat brown in coloration, and that persisted most of the way down the runway until, well, the two main tires went off the left side of the runway. We've taken several photographs of these marks, but it's hard to -- to discern them in photographs because of the light angle, but they were definitely visible on the surface, and the fact that, first of all, they were present indicates to me that some forces were developed between the tire footprint and the -- and the wet pavement, and, secondly, -- Q Tom, they've -- MR. ZWINGLE: Excuse me. Mr. Chairman? CHAIRMAN HALL: Yes, sir? MR. ZWINGLE: Would the witness identify this photograph, please? CHAIRMAN HALL: Yes, and while you're at it, Mr. Yager, for the benefit of the audience, you might try in layman's terms as much as you can to explain what you mean by "scrub mark". THE WITNESS: Okay. Basically, it's a cleaning of the surface compared to the -- what the surface looks like immediately outside of these tracks, and visually, it's a -- it is like a scouring or a white-appearing track on the pavement that is lighter in color than the adjacent areas either side of the tire mark. In that photograph there, you can just barely make them out. This is looking down Runway -- CHAIRMAN HALL: And this is the Little Rock runway? THE WITNESS: That's correct. The Little Rock runway. BY MR. PEREIRA: Q Tom, could you try to point those out, if you can see them from there? I believe on the right-hand side there, there's two light -- there you go. A Yeah. Right -- right in here are two of the white marks or scrub marks that I'm indicating coming from the main gear tires, and it's interesting to note that we not only got marks from all four main gear tires, we also got similar marks from the two nose gear tires, and hence this isn't due just simply to the braking action between the tire and the pavement, it's due to the steering forces being developed between the tire and the pavement. Q Did those marks lead all the way up to the marks going through the grass and to the accident site? A They did, and in fact, in some cases, they went across the 500-foot paint marks that delineate the first 1,500 feet of the runway, and our first -- well, I forget now what the increments are, but they're 500 feet apart, and some of those paint marks are surrounded by black paint as well as white paint, and in looking at those areas where the tires went across the black paint, you got a shiny appearance on the black paint, like it had removed the oxidized material from the paint, whereas right outside the tire track, the paint looked somewhat opaque and dull, but right in the wheel track on the black paint, it was highly glossed in a bright appearance. MR. PEREIRA: The Allied Pilots Association, I believe, asked for identification of that picture. I believe it was supplied to us by American Airlines from some of their helicopter runs. MR. ZWINGLE: The point I was trying to make is that the marks that Mr. Yager were referring to were not clearly visible, and I'm not certain they were visible to the back of the room, and that the -- the dark black skid marks were not from the accident aircraft. Those skid marks would indicate some type of traction of some -- THE WITNESS: Right. MR. ZWINGLE: Okay. THE WITNESS: Yeah. That was in an area near the touch down of the runway, and hence those other black marks were present. MR. ZWINGLE: Thank you. MR. CLARK: Mr. Yager, the black skid marks would indicate what? THE WITNESS: Would indicate high friction where the sacrificial member is now the tire rubber, and it's being deposited on the pavement. MR. CLARK: Do you get that on a wet runway or dry runway? THE WITNESS: You get that on a dry runway. MR. CLARK: All right. THE WITNESS: Right. BY MR. PEREIRA: Q You touched on it briefly, but could you again summarize the effect of yaw angle on an airplane's breaking performance, and does NASA have simulation tools to estimate these effects? A Yes, we do. We use our Aircraft Landing Dynamics Facility primarily to look at these effects. If I could go back to Slide 18, I believe it is, in the exhibit, where it shows the variation of friction coefficient with slip for purely braking and combined braking and cornering. These curves here were developed from test runs made at our track facility at Langley, and we've subsequently used this data to implement a tire modeling program to use on the simulator at Langley, and also in the mid-'70s, we used it on a simulator out at Long Beach to -- to duplicate DC-9 performance, and I know in the tests out at Long Beach, where we had a variety of dry, wet and flooded runway conditions, including patchy runway conditions, we had available to us several American Airlines pilots that flew the simulation, and several other airline pilots that had thought the modeling of the friction coefficient was quite good. And again, when you have a demand for cornering, it's going to compromise your ability to brake and vice versa. Q Okay. Do the rainfall, surface texture and runway crown data indicate that some portion of Runway 4 Right may have been flooded, and, if so, how deep would the water have been? Could it have caused hydroplaning, and do the rest of the data that we have indicate that it did cause hydroplaning? A Okay. Based on the parameters of wind speed and direction, the transverse slope and longitudinal gradient of the runway, the macro texture of that that were measured, I feel on the right side of center line, in the pilot's position, there would not be enough water to sustain dynamic hydroplaning. Now, on the left shoulder, which is the upwind shoulder of the runway, due to the wind effect of stacking the water, in other words, with the runway crown being the peak, and the wind trying to hold the water on the runway, you're going to start developing an appreciable water depth on that left side. In particular, in that 13-foot area that is not grooved, that portion could have supported dynamic hydroplaning, but the evidence on the runway where the airplane was traveling in that area down near the 1,000 foot remaining marker, and just prior to the two main gears going into the grass, we still have the white marks. So, for some reason, in that particular area of the runway, we didn't have the water depth necessary for dynamic hydroplaning. Q And the grooving on the tire would help alleviate that? A Would help alleviate that. That's true. Q Okay. A And, of course, at that area -- area of the roll-out, he was down close to a hundred or 95 knots -- I believe he exited the runway at 90 knots. So, he was below his critical hydroplaning speed. Q Okay. Should runway conditions, such as you just mentioned, be monitored and reported to crews, and, if so, how could this be done? A I definitely feel runway conditions should be monitored and should be reported to the crews operating on the runways, not only those landing but those taking off that might have a need for a rejected take-off. This can be done visually, and it can be done on the basis of weather activity. I mean if you have a period of time where in the summer months, there is no appreciable precipitation, the frequency of these inspections doesn't have to be as much, but, in addition to visual inspections, I think in terms of knowing if you have any ponding problems on a runway, you should also take friction measurements with some of these ground vehicle devices. They do give reliable and repeatable data, and the normal mode of operation is to go the entire length of the runway, and then give values for each third of the runway, so that you have a value for the touch down area, the middle braking portion of the runway, and then the roll-out area at the far end, and having those three relative friction values does give the pilot some sense of appreciation of how good his stopping capability's going to be if he has to go with full brakes. Q Are there automated systems, sensors in the runway, that can provide this information to the tower? A There are some sensors available now to airport operators and also highway maintenance people that detect the presence of water, the presence of ice on a pavement surface. They will also indicate temperature, and the newer ones will indicate depth, and if I'm not mistaken, Runway 4 Right, 22 Left at Little Rock, has two of these sensors installed in that runway to give them an appreciation of any water forming on the surface. Q Do you know if that data is provided to the tower or -- or to the ground operations? A Normally, the units that I've seen at other airports, it's provided directly to the tower in a CRT display, and some runways have as many as six or eight of these sensors on both sides of center line and at either end of the runway. Q And do you believe some kind of automated system like that should be required for airports that have air carrier operations in to and out of them? A Well, it would definitely help in their assessment of knowing what the runway conditions are at any point in time. If you've got to go out at night time and inspect the runway, there's only so much you can see, and these sensors would aid in night time operations. Q Do you know if they have a history of maintenance problems or accuracy problems? A My understanding is that they're quite reliable, and some units have been installed as long as 10 years. The one at JFK, I believe, is 10 years old. Q Thank you. Based on your knowledge of the entire data set for this accident, do you think we had normal or abnormal antiskid operation, and could you show Page 19 from your exhibit during your answer? A Right. Well, one of the big drivers for antiskid operation is having the weight on the main gear tires, and with the fact that the DFDR data indicates the spoilers were not deployed, this factor of weight was not available to improve the braking force or the cornering force on the tires, and hence I would expect abnormal antiskid operation. Of course, as we all know, the pilots did select manual braking, and my understanding of the antiskid operation on the MD- 82, even if they had selected auto braking, the fact that the spoilers didn't deploy, they wouldn't have auto braking available to them. Q Do you think we got good wheel spin-up? A Yes, I do, based on the vertical velocity that's measured on the DFDR, and the fact that he was near center line on the downwind side, and the wind would have an effect on minimizing the water depth in that area. Q The data do show that we got brake application after touch down. So, therefore, those two things in mind, would you expect normal antiskid operation in this case? A Well, again, the antiskid itself would act normally, but the braking force developed would be considerably less than what I would expect because of the fact of not having the spoilers deployed. Q Okay. Thank you. So, in summary, during your on- scene and subsequent investigation of this accident, have you found any evidence of dynamic hydroplaning, viscous hydroplaning, or reverted rubber skidding, and in answering this, would you please explain how you came to your conclusions for each phenomena? A Yes. I guess the best way would be to go back to Figure 8, I think, in the exhibit that depicts the three types of wet pavement friction losses, viscous, dynamic and reverted rubber skidding. First of all, starting with viscous rubber, viscous hydroplaning, we had good micro texture. We had grooving, and we had better than average tread groove depth remaining on the four main gear tires, and on that basis, I found no evidence of viscous hydroplaning occurring on the runway. The fact that we had these scrub marks on the pavement eliminates dynamic hydroplaning. Under dynamic hydroplaning, your tires are basically behaving like a water ski. They've lost contact with the pavement surface. They're riding on a film of water, and you can't develop any braking or cornering capability. The fact that we had these scrub marks on the surface, the pilot was able to bring the airplane from a severe right drift back across the runway and then rotated it again, indicates to me that dynamic hydroplaning was not a factor in this accident. In terms of reverted rubber skidding, good pavement texture, the grooving, helped eliminate that as a probable cause in this -- in the performance of the tires on the pavement at -- on Runway 4 Right. We found no evidence of tread rubber reversion on the surface, which, in earlier accidents, I have found granulars of rubber on the surface that were reverted, and we found no evidence of tread reversion on the -- on the four main gear tires. This would be reflected in a flat spot on the tire with molten rubber around the periphery. This was not in evidence on the four main gear tires of the MD-82. So, in that respect, these three types of losses on wet pavement were not present, but by no means do I want to indicate that the water on the runway had no influence on the braking and steering capability of the tires. It definitely degraded that capability, and -- but there were other factors that entered into the decreased stopping performance of the airplane, including, of course, not having the spoilers deployed. Q Could we put up Slide Number 11 from your exhibit again, please? For both aircraft, this slide shows that the wet grooved friction is essentially identical to the dry friction obtained. Would not having the spoilers deployed affect where the wet grooved friction effect of friction curves -- A Yes, it would. In both of these instances, the spoilers -- the spoilers were deployed prior to brake application. We have tracked data that -- that indicates the -- the effect of -- of lift on the ability of the tire to develop effective friction coefficient values, and -- and I believe we've got it for the tire sizes that's on the MD-82, but I'm not sure. I could look at that when I got back to Langley next week. Q Okay. In general, would it have the tendency to reduce the wet friction shown there? A Yes, it would. Just how much, I hesitate to say right now. Q Okay. A These tires were at a different pressure, of course, than the MD-82, and that would have an influence on it. Q Okay. Again based on your knowledge of all the data that you're aware of for this accident, how did the flight crews control techniques, control inputs, or lack of control inputs affect the braking performance of this airplane? A Well, first of all, I want to make sure everybody understands I'm not a pilot, and what they did during this event is -- is hard for me to say yea or nay on, but I -- I am impressed by the fact that they were able to recover from this right drift that occurred shortly after touch down, and to my way of thinking, that further substantiates the fact that they were developing some forces between the tire and the pavement, and the scrub marks substantiate that. The -- not having the spoilers deployed was, I think, a key element in not realizing the normal stopping distance that they would expect to get, and then the delay in applying full braking may have compromised their stopping capability. I hesitate to say how much, but I think the manufacturer would have more data in this respect. Q Okay. Thank you. Have you done any energy calculations to try to estimate how much of the kinetic energy was reduced on the runway during its travel down the runway? A Yes, I have. Just simply based on one-half of the mass times the velocity squared, when you consider it touched down at a 150 knots and left the runway at 90 knots, and you work out the numbers, that's about 56 percent of the total energy it took for the airplane to come to a stop at the end of the embankment. So, he was developing somewhat greater stopping forces than one at first realizes, and possibly another 500 feet of runway, he might have been able to stop him. Q Okay. Thank you. Another question. Could there have been partial tire contact patch detachment and still leave the marks that we had? A There could be, but again the marks, the width of them, and the way they varied as the -- as we know the plane yawed going down the runway does not indicate that -- well, I would have to say less than half of the footprint was supported by any type of water. It would be in the neighborhood of 20 percent at the most, based on the width of the scrub mark versus the normal width of the tire footprint area. Q Okay. And would there have been any tire mark or other runway evidence of viscous hydroplaning? A No, there would not. Q Thank you, Mr. Yager. That concludes my questions. CHAIRMAN HALL: Very well. We will move to the tables. I think it's American Airlines to start this out. In fact, am I correct on that? Ron, you went first last time, didn't you, or -- MR. HINDERBERGER: I frankly don't remember. CHAIRMAN HALL: You were sort of scowling. I just was concerned that I had overlooked you. No? Okay. Well, American Airlines? MR. BAKER: Thank you, Mr. Chairman. INTERVIEW BY PARTIES TO THE HEARING BY MR. BAKER: Q Good morning, Mr. Yager. Can you kind of draw all this together from a layman's point of view, and give us your view on what you attribute the minimal traction experienced by Flight 1420 as it traveled down the runway? Can you kind of paint that picture from beginning to end of the factors? A Okay. From the point of touch down, I think the friction level was good. The tires should have spun up due to the fact that he was near the center line. He was on the up wind side of the runway, and the sink speed at touch down was fairly high, which is a recommended pilot procedure for wet runway operations. The tire marks started shortly thereafter and went off to the right side of the runway where he was able to bring the airplane around and start going back across the center line. At that portion, he had not applied any substantial wheel braking, and all the forces developed between the tire and the pavement were going into his steering requirements, and, of course, at those speeds of above a hundred knots, he was getting some steering, of course, from the aerodynamic forces, the rudder and the -- in particular. And then once he starts going from the right side of the runway to the left side of the runway, he's getting more thrust reverser. He's started applying full braking, although my recollection of the DFDR, that took about six seconds from the time the brake pedals started moving till the time he got to full pressure, and, of course, at 200-250 feet per second, that eats up a lot of runway. And nominally in terms of friction coefficients, in that area where he goes from the right side of the runway to the left side of the runway, I would expect in the neighborhood of between .1 and .15 friction coefficient for -- for braking. He's in the center line portion, and that would be the least amount of water, and then, of course, when he gets off on the left, there is more water present on that side based on the wind direction, speed and the fact that the last 13 lateral feet of the runway are not grooved, it's a lower texture, you would suspect that he would get into a hydroplaning situation there. The marks, however, indicate that the tires still were maintaining some contact with the pavement, even on that non- grooved portion, just prior to going into the grass, and the longitudinal acceleration trace does not reflect any rapid decrease or any change in braking effort. I don't know if that completely answered your question or not, but -- Q Yes. Yes, it does. Thank you. The friction on the runway, the steerability of -- of the tires, and aerodynamics all play into the control of the direction of the airplane. Would you agree from your analysis that pilot control and input probably accounted for the initial skid recovery as opposed to steerability of the -- of the tires themselves? A Right now, I've got to say it was a combination due to the fact that we had the scrub marks in the area where he brought the airplane back around to the center line. Q Have you calculated how fast this airplane would have been going had it -- had the runway been flooded, and it had rolled 5,200 feet without spoilers? A No, I have not. Q Are you aware or -- or have you considered actually doing this operation in a simulator to verify your thoughts? A No, I have not considered that possibility. Right now, we do not have a sim at Langley that would replicate the MD-82 configuration. Q Have you ever used flight simulators to replicate these kinds of events, and are they useful in your work? A They are. They are quite useful, and like I say, I spent several weeks in Long Beach in the '70s developing one on -- on the DC-9, and they can be quite useful. Q Was there any testing done on this particular runway to depict what would have been a flooded runway condition? A We in our drainage test in November were basically trying to identify if there were any areas on the runway that would produce flooding, and admittedly, we didn't test every foot of the runway, but we did it in 500-foot increments, and in no case was there a ponding problem on that runway that would create a flooded condition. Q So, that's a -- but that's a drainage test, not a test of the effects of flooding on this runway, including the crosswind? A That's true, and in order to do that, we'd almost have to rely on Mother Nature. A tanker truck wouldn't -- wouldn't be able to supply water fast enough to flood that runway. Q Has that work ever been done in -- in other events? A Yes, it has. I was involved in a T-38 accident at Ellington Air Force Base in the late '70s, where a T-38 with one of our shuttle astronauts on it landed, and it was right at the runway intersection, and there was as much as an inch and a half of water there that we found during subsequent tests with a tanker truck, and his tires never spun up on touch down, and he went off the side of the runway and ended up on a taxiway. Q Would you -- would you characterize that as hydroplaning or what was your conclusion? A Well, the conclusion there was that where he touched down, he got into dynamic hydroplaning, no wheel spin up. He applied no brakes whatsoever during the entire roll-out. When he came out of the pond, his tires did not spin up again. They stayed in a non-rotated condition and reverted rubber developed, and we got very distinctive white marks on the pavement that were much -- much more distinctive than the marks that I saw out on Runway 4 Right, and these persisted all the way to the edge of the runway, and then the plane went through about 400 feet of grass and mud and stopped on the taxiway, and both main gear tires still had tread rubber reversion in the skid patch on that particular airplane. Q That -- that pattern of white marks, were they uniform all the way down the runway? A The pattern from the T-38 was, with the exception of the last hundred feet, where he started yawing left, and they became a little bit wider in that area. The width of them became wider. Q Would you describe the pattern you observed on 4 Right left by 1420 to be uniform all the way down? A No, I would not. They varied in concert with the -- the aircraft yaw angle. They started out being one width, and as they approached the right side, they became somewhat wider. Q Have you seen the -- observed the tires on the airplane since the accident? A Well, a couple of days after the accident is when I observed them. Q And I think you -- you indicated earlier that you saw no reverted rubber on -- on those tires, is that correct? A That's correct. Q Have you -- have you ever been involved in an event in which the reverted rubber was removed as a byproduct of going through the mud and terrain as this airplane did? Is that possible in your view? A It's possible, but like I say, I've observed this T-38 accident where it didn't happen. Q Are -- are there any other tests that you're familiar with or you could recommend that these tires could be put through to ascertain if -- if in fact there had been rubber reversion, other than simply a physical observation of -- of the tires? A Not at this time, I do not know of any laboratory tests. Q You showed us a chart of stopping distances based on some work done with a Conveyor 880 which, if my memory serves me right, is an airplane of the vintage of the early '60s. Have newer charts been developed representing today's aircraft, such as the Super 80? A We do not have one for the Super 80, but we've got one for the 757. Q Do -- do they match up pretty well, if you take all the dynamics involved with the 880 material? A Actually, you get better friction coefficient and better braking compared to the 880. Q In your opinion, were the wheels turning as the aircraft went through the grass after it exited the left side? A Yes. We've done tests, just as a footnote, on several different soil surfaces in support of Army and Air Force operations, and we found that once the tires lock up or are stopped rotating on a non-rigid surface, they tend to bury themselves, and the landing gear would -- would shear off, and that's one reason why I think they were -- they were rotating. Q You indicated that parts of this runway would reasonably considered -- be considered to have been flooded. If it has a water depth of 0.10 inches, what rainfall rate would it have taken, given the -- the runway friction surface and drainage and all the rest, for 4 Right to be considered to have been flooded? A Two inches per hour. This is at an area 15 feet from the center line. Q Even with a well-constructed runway that has good grooving and crowning, is it possible for there to be a rainfall rate or an accumulation so great that the design of the runway could not evacuate the water leading to ponding, pooling, or standing water on the runway? A There -- there could be that situation, if the surrounding terrain, the non-paved portion outside the runway shoulders, was such that it acted as a dam. It did not have the cross fall that the runway itself had, and then the other factor would be the wind. If it was a no-wind condition, that -- that would contribute to an accumulation of water. Q Do you believe that the crosswind conditions that you heard in the testimony the last two days may have contributed to the flooding on this runway? How would you describe that? A Well, the -- the crosswind that was present from the pilot's position left to right would mean that on the left side of center line, the water would be what I termed "stacking". It would be accumulating because the wind effect would be to slow down the drainage of any water that exceeded the -- the groove depth and the texture depth, whereas on the downwind side or the right side of center line, it would increase the drainage capability and literally blow the water off the surface. Q Now, on either side of the hard surface of this runway, it's -- it's grassed, as -- as we all know. Do you have an opinion as to -- or -- and did you do any work to ascertain the effect on the drainage of this runway having to do with the height of the grass on the day of the accident or the nature of the soil on either side of the runway? Did you -- did you look at that aspect of this at all? A We did in November, when we did the drainage test, and as you know, there's no way of telling with certainty how the soil/grass terrain was comparable to what was present in June. Admittedly, in November, the grass height was greater than the pavement height, and once the water reached the edge of the pavement, it started disappearing into the grass, and you could see it trickling outward. There was still a gradient there, but the -- the rate that the water went out from the edge of the runway was definitely slower than what was on the paved runway, but part of that is due to absorption by the soil. Now, I did not take any soil samples to determine the moisture content and that type of thing, but I was mainly interested in the paved surface when did those drainage tests. Q So, if I could summarize, you didn't do any specific assessment of the drainage capability of -- of the soil structure, and - - and you believe that the height of the grass can have an effect on the damming and the drainage characteristics of a runway? A Yeah. Just visually, I have observed the water slowing down, yeah. Q Thank you very much. CHAIRMAN HALL: Allied Pilots Association? MR. ZWINGLE: Thank you. BY MR. ZWINGLE: Q Mr. Yager, with reference to the T-38 accident at Ellington Air Force Base that you mentioned previously, the marks left on the runway by the tires traveling down the runway, were they uniform in color throughout? A Yeah. From the time he left the ponded area till the time he exited the right side of the runway pavement, they were uniform in color. Q Okay. But they were not uniform in dimension, correct? A That's correct. Q In order to leave these distinctive marks on the runway, is it necessary to have water between the tire and the runway? A Yes, it is. Q Okay. With regard to Exhibit 13A, Page 5, -- do you have that, sir? A Yes. Yes, I do. Q Okay. The date of the exhibit I have, I believe, is the 20 -- I'm sorry -- the 6th of January '99. Is that the one you have? A No, it isn't. MR. CLARK: 2000. MR. ZWINGLE: Does it say '99? MR. CLARK: I think it does. MR. ZWINGLE: Now I know where the Y2K problem lies. THE WITNESS: Okay. I've got it. BY MR. ZWINGLE: Q The second paragraph from the top states, mid- paragraph, that "the runway's capable of handling rates up to 1.4 inches per hour", and I believe you stated that in your belief, the runway's capable of handling up to two inches an hour, is that correct? A That's correct, based on the combination of both cross fall and macro texture. Q From the testimony that was given yesterday by our meteorology experts, do you recall the definition of the Level 5, Level 6 NWS VIP scale thunderstorm? A Not specifically, but I understand that's a severe rain storm. Q Okay. Do you recall that the Level 5 thunderstorm is defined as capable of producing rainfall intensity of over 2. -- up to 2.5 inches per hour? A Yes, I do. Q Do you recall that the NWS VIP Level 6 thunderstorm is capable of producing rainfall up to 5.5 inches per hour? A No. I thought it was even higher than that. 7.2, I thought. Q I'll take it. A Anyhow, -- Q Based on that, -- A -- I was -- Q Based on that rate of rainfall, could this runway have been flooded? A Oh, yeah. Q Given that the thunderstorm existed? A Right, and there was no wind. Q Okay. With regards to the crosswind that existed, does not your statement that the left side of the runway would be flooded and the right side of the runway would not be flooded, does that assume that the water on the left side of the runway cannot transgress the center line? A No, that doesn't assume that. Q Okay. Then with the velocity -- A But -- Q -- of the winds -- with the velocity of the left crosswind, cannot water on the left side of the runway transgress to the -- the center line and augment the precipitation already falling and accumulating on the right side of that runway? A It could, if conditions were severe enough, and right now, I do not consider that the conditions that severe. I consider the fact that with the crosswind, the flooding on the left side would have gone up to about 15 feet from center line. It would not have exceeded the center line, and on the downwind side or the right side of the runway, that water would have been expedited off the side. Q And what value of wind velocity would you use in that assumption? A This would be a value of 20 knots. That would accommodate stacking the water depth that was greater than the macro texture, and the macro texture of the -- of the surface, at least in the middle portion of the runway, was like .05. Q Why would you use the value 20 knots in that assumption? A Based on experimental data that we've collected at other runway sites, where winds have been present, and under similar cross fall conditions. Q Now wait a minute. The crosswind conditions during the period of precipitation prior to the accident, when precipitation began, which was approximately, I believe, 15 minutes prior, did we not have or do you recall evidence that crosswinds in excess of 20 knots existed? A Yes. Q Did you conduct friction tests in the non-grooved portion of the runway? A No, we did not. Q Your -- your term -- the term you used "scrub", is that defined anywhere? Do you have a definition for that term? A It means a change in the coloration of the pavement in the surrounding area, the area outside of the scrub mark. Q Okay. And can you account for that change? A Due to the tire footprint pressure acting on the wet pavement. Q Solely pressure? No friction? A Well, pressure produces friction, and friction results in the scrubbing action, and that friction can be both cornering and braking -- and/or braking. Q Can you state conclusively that the accident aircraft did not -- I'm sorry. Let me restate that. Can you state conclusively that the accident aircraft experienced wheel spin-up? A I guess it's a matter of interpreting the term "conclusively". Based on prior knowledge of how aircraft tires behave, under wet pavement conditions, I would say they would have spun up. Q But you've referenced DFDR data with regards to the spoilers. Do we have conclusive evidence from your examination of the DFDR that there was wheel spin-up? A Well, one parameter that I look up -- look at in terms of wheel spin-up is the vertical acceleration at touch down, and if it's above one g, I consider that a firm to hard touch down, and that helps in allowing the tire to penetrate whatever water depth there might be in that area and rapidly spin up within a second to at least the threshold velocity where the antiskid would start operating. Q And that would be even including momentary contact? A Yeah. Momentary being in the -- in the neighborhood of a half a second. Q Do you agree that the marks left on the runway for at least one of the main landing gear, and I believe it's the left main landing gear, and the nose gear was not continuous with that of the right main landing gear? A Yeah. There were some gaps. Q There were some gaps? A Yeah. We've got, of course, a chart of those wheel tracks, if you want to look at it. Q Yes, I'm familiar with them. I asked that question for clarification. The question was asked by American Airlines regarding the possibility of -- of evidence being removed from the tire due to its travel through the non-runway surfaces. Did you sift the soil between the end of the runway and the point where the aircraft stopped? Was there any soil sifting? A There was no soil sifting. Q In your opinion, do the main landing gear tire marks indicate that braking appeared -- braking occurred? A It's hard to distinguish in just looking at the scrub marks where they're -- how much is attributed to braking and how much is attributed to cornering. It's a combination thereof. Q If the antiskid system were in operation and was cycling, and do you understand what I mean by cycling, would you expect the appearance of the tire marks to change as the antiskid cycled on and off as pressure -- A Yeah. If the -- if the airplane was in a non-yaw position or non-yaw attitude, I would expect the marks to change. Q Did you notice a change in the appearance of the marks? A Well, I noticed a change, but it wasn't in the area where there was any braking, wheel braking. Q Could evidence of reverted rubber have been washed away by the heavy rainfall and wind? A Yes, it could have. Q My last question. Can you offer an explanation as to why American 1420 exhibited a deceleration rate of only 10 knots per thousand feet? A Basically, it was due to the amount of energy required for directional control that compromised his deceleration level, and the fact that the spoilers were not deployed. So, then -- when he did get into a braking -- a tire-braking mode, the braking force was not as high as what it should have been with the full load on the main gear tires, and those are the two main reasons. MR. ZWINGLE: Excuse me, Mr. Chairman. I have to retract the preface that this will be my last question in response to -- to this response. BY MR. ZWINGLE: Q Do you know conclusively that the spoilers did not deploy on landing? This is not to say that the spoilers were found in the retracted position. A All the evidence that I've seen that has been collected relative to the accident indicates the spoilers were not deployed. Q And that evidence is? A Basically the DFDR and the -- well, basically the DFDR. Q And -- and do you know the sensing parameters of the DFDR with regard to the spoiler system? A Well, I've got -- I've looked at a copy of the DFDR tracings. Q But do you know -- are you aware of the sensing parameters? How many spoiler panels are sensed -- A Oh, okay. Q -- in sensing -- A Yeah. Right. Two. Two are sensed. Q Have you conducted any study on the -- on other similar air carrier accidents with regards to wet runway overruns or -- A Yes, I have. Q -- contaminated runway overruns? A Yes, I have. Q Can you tell me which ones you're familiar with? A There was one involving a Portuguese airliner, a 727, in Fucho, Madera. Looked at a DC-9 accident at Baton Rouge, Louisiana. Well, the one in Baton Rouge, Louisiana, went off the side of the runway, not the end of the runway. Looked at a 737 aircraft that went off the end of the runway at LaGuardia. There's -- there's been a number of them. I'd have to -- Q Korean Air -- Korean Air MD-80 in Korea? A I did not look at that accident. Q Have you been able to draw any similarities since the occurrence of this accident and -- and previous accidents you've looked at? A Well, the one involving the DC-9 at Baton Rouge was reverted rubber skidding. There was evidence on the tires. The 737 at LaGuardia, we had the scrub marks, but we didn't have tread reversion nor viscous nor dynamic hydroplaning. Yeah. Basically, when I came to support the NTSB investigation team in June on this accident, I -- I did do some comparisons with my experience with other accidents. Q No further questions. CHAIRMAN HALL: The Association of Professional Flight Attendants? BY MS. LORD-JONES: Q On airplanes with no wheel spin-up, which are not locked, will braking systems work to his knowledge -- to your knowledge? A They will not work effectively because they don't have a speed reference to go by. They need a wheel speed reference to develop the necessary brake pressure to develop braking forces. Q Thank you. CHAIRMAN HALL: National Weather Service? MR. KUESSNER: No questions, sir. CHAIRMAN HALL: Little Rock National Airport? Maybe the Little Rock Airport -- Mr. Yager mentioned sensors in your concrete out there, your -- MS. SCHWARTZ: Yes, sir. CHAIRMAN HALL: -- pavement, and he didn't know where they are read out. Where -- where are they read out? MS. SCHWARTZ: Sir, I don't have the answer to that at the present time, but I can obtain the information. CHAIRMAN HALL: If you could, and let us know, we'd appreciate that, Deborah. Thank you. MS. SCHWARTZ: Very good. CHAIRMAN HALL: Go ahead. BY MS. SCHWARTZ: Q Mr. Yager, if more brakes had been applied earlier and spoilers had been deployed, are you able to tell us whether you believe the aircraft would have stopped safely on the runway? A My cursory calculations indicate that it would not have been able to stop on the runway due to its touch down position and having only 5,200 feet remaining. I think a later presentation this morning will get into more details on that. Q Thank you. Under your definition ranging from wet to flooding identified in an earlier overhead, how would you characterize the runway condition at the time 1420 touched down? A It varied from wet on the right side of center line to a flooded condition on the left side. Q To clarify, do you believe there was any -- you have just referenced wet to flooding. My question, which was posed before -- which I had prepared before you answered, to clarify, do you believe there was any flooding on the runway during the landing of 1420 or could you elaborate? A Well, based on the available weather information that has been discussed yesterday, I would suspect there would be flooding on the runway. It would be primarily on the left side, and it would be primarily in the area that didn't have the grooving, and due to the crosswinds, the -- the area to the right of center line would be under a wet condition. Q Continuing in response to that, if you're characterizing the flooding as primarily being in the non-grooved portion of the runway surface, would you say then that there was any flooding in the grooved portion of the runway surface? A Yes. Knowing the -- the time frame of the -- of the rain shower event, I would suspect that the flooding had gotten up to within probably 15 feet of the center line prior to Flight 1420 touching down. Q Prior to, but at the time of landing, sir? A At the time of landing, up to within 15 feet of the center line. Q Do you believe there was any ponding on the runway during the landing? A Based on the transverse gradient measurements that I took in June, and then the later drainage measurements in November, I found no evidence of areas that would produce flooding. In other words, there were no low spots in the runway that would -- would pond. Q Okay. Again for clarification, you just said that there would be no areas that would produce flooding. In an earlier response, you said there was flooding. Were you using flooding and ponding interchangeably in your last response? A Okay. I -- I can see the dilemma here. In the drainage tests, we were applying water on center line and measuring how long it took that water to go from center line to the shoulder, and in each case, in 500-foot increments down the runway, that time element remained fairly constant at between .77 and .75 feet per second. Admittedly, under a rain shower event, the entire runway is getting wet, and as the rain shower continues, and it changes in intensity, the -- the water depth on the runway is going to start to increase at the edge and then move towards the center line which is the high point on the runway, and under those situations of a natural rainfall event, you could expect water depths exceeding a tenth of an inch on that left shoulder area. Q Can you tell me if your flooding conclusion is based on the actual rain event or based on your test results? A It's based on test results, and the chart that I showed in my presentation, which uses transverse slope and average texture depth as the two parameters in determining the rainfall rate necessary to flood to within 15 feet of the center line. Q Did the water between the runway and the tire which caused the scrub marks cause hydroplaning? A No, it did not. Q Thank you very much. CHAIRMAN HALL: I don't guess those sensors have recorders on them, do they? THE WITNESS: Some of them do, the newer ones. CHAIRMAN HALL: Did we get that? THE WITNESS: Whether or not -- CHAIRMAN HALL: Look into that, Mr. Feith, and find out whether the sensors at the airport have a recorder capability? All right. The Little Rock Fire Department? MR. CANTRELL: No questions, sir. Thank you. CHAIRMAN HALL: All right. Federal Aviation Administration? BY MR. STREETER: Q Mr. Yager, I've got two values down here. I probably missed something, but I -- I heard you say that the runway configuration as you examined it out there on 4 Right would accommodate either 1.6 inches or two inches of rain per hour. Which -- which was correct there, sir? A Oh, okay. The 1.6 inch value was based on the two inch spacing, quarter inch width and three-sixteenths depth of the grooves on Runway 4 Right. If you take into account what the current AC recommends of one and a half inch spacing, quarter inch deep, quarter inch width, it would bring that required rainfall rate up to two inches. Q Okay. So, -- so, the actual configuration that existed on the runway at the time, the 1.6 inches, is what you would expect it to accommodate? A Right. MR. CLARK: Let me clarify that. If that's coming out of the 13A, Page 5, it's 1.4. MR. STREETER: All right. BY MR. STREETER: Q And that's fine because the key point here is not so much the value as I'm trying to determine when you say it can accommodate that, what do you mean by accommodating? Does that mean that that -- if we exceeded that level of rain, it would move into what you're defining as a flood condition? A Right. The other factor that goes into the equation to determine what rainfall rate produces flooding is what is the path length from the center line that you're interested in determining where flooding occurs. Now, that particular chart was set up to indicate flooding in an area 15 feet off the center line. Now, if you went to 30 feet off the center line or 60 feet off the center line, you would get a different rainfall rate. It hinges on the drainage path length. Q Well, just so I'm aimed in the right direction, if you did go 30 feet off the center line, would it be a greater or lesser rainfall rate to flood the runway? A Lesser rainfall rate. Q A lesser rainfall rate. A Right. Q Okay. So, for your -- for the purposes of -- of what you're observing that night, then your judgment that this was a wet runway -- and let me make sure I have that definition right. For your purposes, the wet runway was less than a tenth of an inch of water on the runway, is that correct? A Less than .01. Q .01. A .01 to a tenth of an inch. Q Okay. A Excuse me. Q All right. A You're right. Q Okay. .01 to a tenth. A Right. Q So, -- and -- and your -- in your judgment that night at the -- at the position you believe that the pilot would have been at, laterally on the runway, it was -- it would have been a wet runway? A That's -- that's correct. Q Okay. Now, I believe you stated earlier on a question there with the Little Rock Airport, that this was based on calculations. A That's correct, and right now, they're considered conservative. Q Okay. And that -- and the -- and one of the elements in that calculation was the rainfall rate, and that rainfall rate, I presume, came from the other data that's available? I mean official rainfall rates? A Oh, yeah, and they were -- they were taken from gauges that were located near where we were doing the measurements of the water depth, texture and cross fall. Q Okay. A Yeah. Q All right. Now, at -- at a tenth of an inch then, that's where we're going to shift from your definition of wet runway to flooded runway, and don't let me put words in your mouth. I'm trying to say this to make sure I -- I -- I thought I heard you state earlier that under the conditions that you described, that you had no doubt that there was wheel spin-up on those conditions. If the water depth was slightly greater, enough to move it into the flood stage, would you have the same level of certainty on the wheel spin-up? A No, I would not. Q I believe that -- and this is again where I missed part of the question, but there was a question from Mr. Clark to you regarding the marks, and the answer was that those were marks you would expect to see on a dry runway. I missed that. Was that referring to the scrub marks you observed or the black skid marks? A They were referring to the black skid marks. Q Okay. So, the black skid marks, you -- is -- that's a dry runway trait? A Right. Q And the scrubbing condition that you described then would be a runway with some degradation due to water or -- or contamination? A Yes. Q Okay. Thank you very much, sir. That's all I have. CHAIRMAN HALL: Very well. This witness has got the party tables interested obviously. Boeing Commercial Airplane Group? BY MR. HINDERBERGER: Q One question, Mr. Yager. In your experience, if a -- if a tire on an airplane experiences reverted rubber condition, is there evidence left of that on the tire? A Yes, there is. Q Okay. And were there -- was that condition -- did you see that condition on the -- on these tires of the accident airplane? A No, I did not. Q Thank you. MR. BAKER: Mr. Chairman, I have two quick follow-ups, please. CHAIRMAN HALL: Yes, sir. BY MR. BAKER: Q Mr. Yager, did you get involved or are you familiar with the UPS event in Houston of last year with the freighter? A Yes. That was at Ellington Air Force Base -- Ellington Field, I believe. Q That's correct. A With a DC-10, yes. Q 75 or 76. I'm not sure which. A Excuse me. It was a 76, right. Q So, you studied that particular event? A Right. In fact, they sent all 10 main gear tires to our facility at Langley. Q Are your findings and opinions of that a matter of public record anywhere? A Yes, they are. We -- we gave a report to the -- to the NTSB investigator supporting that -- that accident, we being myself and another engineer in the office. Q Without going into it very far, would you suggest that what you saw there in any way to be similar to what happened to 1420? A It was similar in the fact that in both cases, it was a wet runway. The main difference between Ellington Field and Little Rock is that Ellington Field does not have a grooved runway, and hence the -- the ability to support dynamic hydroplaning was greater at -- in the 767 accident than in the case here at Little Rock. Q So, you concluded there was dynamic hydroplaning there? A Yeah. Q You heard earlier testimony that there's an impression among some of us that follow aviation closely that this whole issue of overruns on wet runways is a bigger problem and growing. Are you aware of anyone trying to do an overall assessment or correlation of these events to see if there are systemic problems we ought to deal with, and are you involved in any of those kinds of efforts? A Right now, I'm mainly involved in documenting any overruns or veer-off accidents that occur under snow and ice conditions, and I know since November through today, there's been at least six mishaps of a variety of airplanes that have gone off the side or the end where there's been no injuries, no damage to the airplane, it's just towed back out and brought back into service, and - - CHAIRMAN HALL: We've made seven, Mr. Yager. We just had one at Newark. THE WITNESS: Oh, okay. And it's these type of statistics that sort of get swept under the runway, and it should be tabulated and should be critiqued as to why it happened, and what -- what were the factors involved, and how can we prevent it in the future? Admittedly, I realize the manpower limits of the NTSB and the aviation community to do this, but, yes, I think there would be value in tracking these mishaps and these incidents. BY MR. BAKER: Q One last question. Back to Ellington for a minute. Were there marks on the runway, and how would you describe or compare them to the marks you saw on 1420 which you described as scrubbing? A Right. The marks on the runway at Ellington were not significant and were not what I'd classify as scrubbing. Q So, they were not similar to this, and I think I heard you say earlier in your testimony that typically with dynamic, there are limited or no marks? A That's correct. Q Thank you, sir. CHAIRMAN HALL: I believe that Mr. Pereira wants to take the floor again. INTERVIEW BY TECHNICAL PANEL BY MR. PEREIRA: Q Mr. Yager, could you put up the slide that shows the rainfall rate and the micro texture values that's centered a lot of the discussion we've been having the last half hour? I believe it's Slide 16. A Right. Slide 16. Q When we say that this is an indication of flooded conditions if you get above these curves, what depth, what water depth is that? A A tenth of an inch. Q Okay. And what -- where would these curves go if we wanted the depth to be at two-tenths or a quarter of an inch? Would they shift up or down? A They would -- they would shift up. Q And what water depth, given the tread depths of the accident airplane tires, would be required to sustain dynamic hydroplaning? A Since the minimum average tread depth was two-tenths of an inch, that would be the value. Q So, in terms of context, would these curves be more appropriate for this accident if they were adjusted to a flooding depth that would cause hydroplaning for this accident airplane? A That's correct. That would be one factor that would raise them and would require a higher rainfall rate. Q Okay. So, then would it be -- do you have any idea how much more than two inches per hour it would be required for our cross slip and our tire depth? A Not immediately, but I can do the calculations and come up with those values for you later on today. Q Okay. And even if we did have a tenth of an inch on the left-hand side of the runway due to the crosswinds and the rainfall rate, do the marks and the tire tread depths indicate that it supported dynamic hydroplaning in the case of this accident? A No, they do not. Q Okay. Earlier, I think there was a question that I was confused on. I believe somebody asked would the rain have washed away the evidence of reverted rubber, and I thought I heard you say yes. Is that true for the tires? Would the heavy rain that occurred and hail have washed away the evidence of reverted rubber on the tires? A No, it would not. What I was referring to was evidence on the runway. In some situations, I have found granulars of rubber that had been reverted, that were a residue on the runway itself, and in this instance, I did not find any of that evidence. Q Okay. And I also thought I heard the airport ask you did you think if this airplane had had brake actuation at an early stage, let's say, consistent with auto brakes or early manual application, and full spoiler use at an early stage, consistent with auto spoilers, do you think it would have stopped on the runway with the wet conditions that we had? A No. Under the conditions -- I understood the question from the airport as being similar but still not having the spoilers deployed. With the spoilers deployed, you are going to get more weight on the wheels and be able to create a higher braking force, but -- well, by the -- okay, okay. Q Would you rather leave that up to Boeing? A Yeah. I think I would. Q Okay. A Because what enters in here is the fact that if he didn't have the directional control requirements, then -- then most of the forces could go into braking. Q Okay. CHAIRMAN HALL: Very well. Thank you. MR. PEREIRA: I had one more, Jim. Sorry about that. CHAIRMAN HALL: All right. BY MR. PEREIRA: Q Lastly, we're talking about flooding on the side of the runway and crosswinds causing it to pile up. It just struck my curiosity that a lot of developments and highway roads seem to have flood control devices, essentially drains, on the side of roads that help take away some of that standing water. Do any runways in the U.S. or around the world have that, and do you think they should? A Oh, yes. There's several runways that have drainage channels outside the edge of the runway to further accommodate drainage. That's more prevalent in England than anywhere else, I guess because of the -- the frequency of rain events over there, but, yeah, that could -- that could help. Q Okay. But it's not a requirement in the advisory circular or anything right now? A No. There are guidelines in the advisory circular relative to water drainage, but not to the extent of culverts or drain -- drains. Q What's your opinion on that, and do you think there should be or would it help? A Well, it would help the drainage, but, of course, you don't want to have an obstruction for the airplane of any consequence. It would have to be properly designed so that tires could roll over them without any impediment. Q Okay. Thank you. That concludes my questions. CHAIRMAN HALL: Who -- I assume there's somebody at the FAA that does this type of technology and work, and we're going to hear from him later? MR. STREETER: We're going to try, sir. CHAIRMAN HALL: Well, good, good. I'll get my engineers even more excited. Mr. Sweedler? MR. SWEEDLER: Yes, Mr. Chairman, I just have one area I'd like to discuss with Mr. Yager. INTERVIEW BY BOARD OF INQUIRY BY MR. SWEEDLER: Q Mr. Yager, you mentioned the far end of the runway was not grooved as was the other parts of the runway, and -- and you also noted that an extra 500 feet, the airplane might have been able to come to a stop on the runway. But my -- my question is, the airplane touched down at - - at about, you said, 5,200 feet remaining. It's a 7,200 foot runway, and if the airplane had touched down earlier on the runway, where it might have been grooved, would that have made a difference in -- in the airplane being able to stop with all the other conditions being similar to what they were with the accident airplane? A No, that still would not have allowed him to stop. I -- I misspoke when I indicated another 500 feet, and then, secondly, relative to the grooving location, I might have used the term at the far end, but what I meant was laterally. The runway is transversely grooved the entire 7,200 feet, but on either edge, there's 13 feet that have not been grooved. Q So, touching down a thousand or 1,500 foot earlier on the runway, in your opinion, would not have still made a difference in the airplane's ability to stop before it went off the end of the runway? A Not if everything else stayed the same. Q Okay. Thank you, Mr. Yager. CHAIRMAN HALL: Mr. Berman? MR. BERMAN: No questions, sir. CHAIRMAN HALL: Sure you don't have one? Mr. Haueter? MR. HAUETER: I'll make up for Mr. Berman real quickly. BY MR. HAUETER: Q You made mention in terms of the wind effect on blowing the water off the runway on to the other side. If the wind had been much higher, say, instead of being 24 knots, it had been, say, 50 knots, would that increase or decrease the flooding effect? A If the wind had been higher, there probably would have been a decrease in the flooding effect because basically it would provide more force to bring some of the water from the left side up over the center line and pushed off to the -- to the right side. This is an interesting situation in that my data right now only goes to about 35 knots, but as the wind velocity increases, you get more -- a greater flow rate of the water that exceeds the macro texture depth, and it's possible that that force could offset what's needed to bring the water up over the center line, at least at a one percent slope, if not a one and a half percent slope, and hence it would help reduce the water depth throughout the width of the runway. Q Thank you, sir. A Okay. CHAIRMAN HALL: Mr. Clark? BY MR. CLARK: Q You talked earlier extensively about scrub marks, and what would you -- if you had steam cleaning on the runway, I assume that's associated with the locked wheel hydroplaning? A With the reverted rubber skidding, yeah. Q What would that look like? What would be the differences between what you observed and what you would expect to observe if you had steam cleaning? A It would be a much more distinct white mark as opposed to the lighter coloration that I observed on the runway at Little Rock. Q Okay. If you exceeded the -- that .1 inch to get into the flooding category, and we touched down at this 149 knots, would that mean we automatically get hydroplaning? A No, no, no. It does not mean that. Speed plays a role. Tire tread groove depth plays a role. Inflation pressure plays a role. Q So, even with the -- something greater, if I were to get something greater than the .1 inch, that's still not a -- A A dynamic hydroplaning situation. Q Yeah. Okay. You -- there was a term earlier called "ratcheting" in the brakes or locked wheel. What kind of evidence would you see if you had a tire or a brake system that was ratcheting? A You would see irregular tire marks, particularly -- that occurs a lot on dry surfaces, and there would be a black mark with an interval of no mark and then another black mark, and it would persist down the runway. Q Okay. If I -- when I landed in my -- if the wheels did not spin up, what would I expect to see? A If the wheels did not spin up, you would see no mark on the runway surface. That would be basically supported by the water film between the tire and the pavement. Q So, we would not have the mark or after a point in time, it would develop into the steam cleaning? A Well, it would develop into the scrub marks that we have, and, yeah, if it remained in a non-rotating condition, it could very well develop into the steam cleaning. Q Okay. But -- and then you just said that it would develop into the scrub marks we had. Does that mean the wheel would spin up and give us the scrub marks we had or the wheel would not spin up and give us the scrub marks we had? A The wheel would spin up and give us the scrub marks that we had. Q Okay. Is there any evidence from the marks that you see that the antiskid was not working? A No. Based on the marks on the runway, I have no evidence that the antiskid was not working. Q If the antiskid were not working, what would you expect to see? A Similar marks that could be attributed to the steering requirements. Q The cornering? A Yeah. The cornering. Q Okay. All right. A It's hard to differentiate from the scrub marks on the runway, how much was attributed to cornering, how much is attributed to braking. Q Okay. How many -- you've worked a number of accident investigations and have an extensive testing career. How many times have you seen evidence of this skidding, this type of skidding marks on a wet runway? How many times have you seen or observed on the runway evidence of hydroplaning that you can correlate back to specific data? A Probably in the neighborhood of 15 to 20. Some of the accidents that I've supported have involved tire failures, such as the Continental DC-10 at LAX. We, being NASA, had a 990 airplane experience tire failure on take-off at March Air Force Base, but those were dry runways. Q What about in the testing environment? A In the testing environment at our track facility, yes, we can duplicate. Q No. I'm asking how many times have you observed -- you -- you're giving us observations of what skidding looks like or hydroplaning or -- or locked wheel hydroplaning. How many times have you observed that and correlated that with data? A Probably a couple hundred times with different size tires, different inflation pressures, going through speed ranges, looking at concrete versus asphalt surfaces, looking at grooved versus non-grooved, a variety of parameters. Q Okay. That's all I have. Thank you. A Thank you, John. CHAIRMAN HALL: Mr. Yager, we appreciate your testimony. You have been with NASA how many years? THE WITNESS: 37. I'm afraid to admit. CHAIRMAN HALL: Well, that's outstanding service to the Federal Government and the people of this country. Thank you very much, and all of it in this specific area. I wish I had that type of concentration. I've wandered about in my career. Well, as has been pointed out by Mr. Baker and obviously the Board is aware of the increased occurrences with runway overruns, and you mentioned, I guess, that we now have, with the event this morning in Newark, seven that have occurred already this year, -- THE WITNESS: Yeah. CHAIRMAN HALL: -- we would certainly welcome any thoughts or final closing comments you would have as it pertains to this accident or this area and things the Board can -- should be considering as we continue our investigation and work. THE WITNESS: Well, first of all, I think it's long overdue that -- that your staff, Mr. Hall, should be commended on the -- on the thoroughness of the investigation at each of the accidents that I've helped support, not only the thoroughness but the open- mindedness of the investigators to consider all possible causes, and with the main thrust being to improve aviation safety. You're an organization that has some demanding requirements, and you seem to meet them to -- to the -- to a very good -- to a very high standard, and with that being said, from my viewpoint as a research engineer and one that's trying to also improve aviation safety, there are several areas that could be improved upon, and some of them were mentioned yesterday, and one of them being the runway reporting. There's much better equipment out there now to give reasonable and comparable friction measurements that pilots can use in assessing runway slipperiness. There are sensors, and there are techniques recommended by the FAA, by the Joint Aviation Authority, by ICAO, to document runway conditions better. The joint program that I'm involved in right now with Transport Canada and the FAA, we're trying to move forward in that area of runway classification, both in terms of condition and slipperiness, and we've achieved a certain degree of success in that we've taken measurements from 13 different vehicles and have been able to harmonize these measurements to all indicate the same value for the same runway condition, and so pilots will not be confused with a new meter reading at Heathrow versus a Saab friction tester reading at Dallas-Fort Worth. For the same conditions they would be reporting the same number. We've got programs scheduled at Langley later this year to look at two other aspects. One, the algorithm for controlling the antiskid brake system. Up until recently, it's mainly been a matter of monitoring wheel velocity or wheel slip speed as the controlling device, and some of the newer airplanes have gone to a GPS system for a speed reference. We're going to be looking at a black box algorithm that relies on brake torque to tell the antiskid brake system when to apply pressure and how much, and it's possible that system would be somewhat more sensitive than present day systems, but we won't know that until we do tests at our track facility. The other thing that we're going to be looking at later this year or early next year is a passive overrun material that, in the event the airplane does suffer a loss of braking or cannot stop on the pavement, this overrun area would be composed of material that would slow the airplane down from a hundred knots to a stop prior to either going into a river or going over a cliff. There's been some work in this area by the FAA Technical Center about 10 years ago, where they came up with a foam concrete material. There's another development here in recent years where it's a material that's composed of both special soil and some composite material that offers even better stopping capability. So, we're going to be looking at those two aspects in our work at NASA Langley, and by all means, we don't pretend to know everything there is to know about aircraft ground-handling performance, and it's from events like this and in discussions with the aviation community that we learn more about ways to improve airplane safety, and I'm -- I'm grateful to be a small part of that improvement. Thank you. CHAIRMAN HALL: Well, we appreciate your contribution, sir, and I think the -- we're going to hear more about the material that might be used at the end of the runways later, if I understand correctly, is that correct, and that was done in response to an NTSB recommendation that was made in the '70s. So, I thank you for the kind remarks you made about our -- my investigators. I'm very proud of the work they do. We have spent a considerable amount of time with this witness, but we've got all day. The National Weather Service has again, if you will look out the window, arranged to have weather that will keep us all trapped in this hotel. So, we may just go -- continue around the clock, but I want to be sure we have enough time to -- to - - you know, we've got important witnesses today, and I want to be sure that we have the time to -- give time to all of them that we need. Why don't we take a break now and come back at half past the hour? (Whereupon, a recess was taken.) CHAIRMAN HALL: We will reconvene this hearing of the National Transportation Safety Board. I'd like to ask Mr. Berman if he would call our next witnesses. MR. BERMAN: Our next witnesses will actually be this panel of three who will have questions addressed to them as a group, and I call Thomas Melody, C.J. Turner and Neal Gilleran. Would you please stand? CHAIRMAN HALL: If I could please -- we've got -- we've reconvened. So, please, if you have conversations, if you need to take -- have them, take them outside the room, please. Thank you. Whereupon, THOMAS MELODY having been first duly affirmed, was called as a witness herein and was examined and testified as follows: Whereupon, CUTHBERT J. (C.J.) TURNER having been first duly affirmed, was called as a witness herein and was examined and testified as follows: Whereupon, NEAL GILLERAN having been first duly affirmed, was called as a witness herein and was examined and testified as follows: INTERVIEW BY TECHNICAL PANEL MR. BERMAN: I'll ask all three of you the basic questions, you're probably used to them, in turn. Mr. Melody, would you please state your full name and business address? MR. MELODY: Yes. It's Thomas J. Melody, and my business address is the Long Beach Division in Long Beach, California. MR. BERMAN: And by whom are you employed? MR. MELODY: Boeing Commercial Aircraft Company. MR. BERMAN: What's your present position, sir? MR. MELODY: I'm the Chief Pilot for Flight Operations, and the Senior Manager for Flight Operations in Long Beach. MR. BERMAN: How long have you held that position? MR. MELODY: For two months. MR. BERMAN: Okay. What was the name of your previous position that you would have held at the time of this accident? MR. MELODY: I was the Chief Test Pilot for the same company. MR. BERMAN: Hm-hmm. And how long did you have that position? MR. MELODY: I had that position for eight years. MR. BERMAN: Thank you. Would you please briefly describe your duties and responsibilities of your current position? MR. MELODY: In my current position, I'm now responsible for the supervision of all of the experimental test pilots, the Training Department, the Production Department, and the Customer Service Department. MR. BERMAN: And do you cover all the Long Beach Division Products? MR. MELODY: That's correct. MR. BERMAN: Okay. Would you please describe your education, training and experience that qualified you for the positions you've had recently? MR. MELODY: Yes. I have advanced degrees, Engineering degrees, both Aeronautical Engineering and Electrical Engineering. I was a graduate of and an instructor at the Air Force Test Pilot School, and I've been a test pilot at Douglas Boeing for the last 14 years. MR. BERMAN: Thank you, sir. And could you please list your FAA airman certificates for us? MR. MELODY: Yes. I have an airline transport pilot rating in the DC-9, DC-10, MD-11, and a hot air balloon rating. MR. BERMAN: Okay. An ability go cope with hot air can be -- MR. MELODY: Yes. MR. BERMAN: -- of benefit sometimes in proceedings. How much time -- flying time do you have in the DC-9 or MD-80 series, please? MR. MELODY: In the DC-9 series, approximately 1,500 hours. MR. BERMAN: Thank you. Mr. Gilleran, we'll go through the same routine. Could you please state your full name and address, business address? MR. GILLERAN: Neal Patrick Gilleran, Long Beach, California. MR. BERMAN: And by whom are you employed? MR. GILLERAN: The Boeing Commercial Aircraft Company. MR. BERMAN: What's your present position, and how long have you held it? MR. GILLERAN: Currently, I am the Engineering Manager for Landing Gear, Brake and Hydraulic Systems. I've been in that position approximately eight months. MR. BERMAN: Okay. Thank you. And what was your previous position? MR. GILLERAN: The previous position was the same role for Landing Gear and Brake Systems. MR. BERMAN: Okay. Would you please describe for me the duties and responsibilities of your current position? MR. GILLERAN: Yes. I currently lead a small group of technical experts, primarily on the day-to-day production support and response to any in-service problems and backing up some of the investigation activity like we have here today. MR. BERMAN: Okay. And could you describe your education and training and qualifications for your position? MR. GILLERAN: Yes. I have a Bachelor's in Mechanical Engineering. I began my aviation career with the Douglas Aircraft Company, working on the analysis of brake system -- brake control systems. I subsequently was involved in the brake control system for the Lockheed L1011, wheels, brakes and tires for the Rockwell B-1, the Northrop F-5 braking system, and subsequently returned to the McDonnell Douglas Company, where I was closely involved with the MD-11 brake control system. MR. BERMAN: Do you have an FAA airman certificate or any other relevant certification? MR. GILLERAN: No, sir, I don't. MR. BERMAN: Okay. Thank you. Mr. Turner, good morning. MR. TURNER: Good morning. MR. BERMAN: Please state your full name and address, business address. MR. TURNER: Cuthbert J. Turner, 3855 Lakewood Boulevard, Long Beach, California. MR. BERMAN: And your employer is? MR. TURNER: Boeing, Long Beach Division. MR. BERMAN: What's your present position, sir? MR. TURNER: I'm a staff engineer in Aerodynamics. MR. BERMAN: And how long have you been in that job? MR. TURNER: One and a half years. MR. BERMAN: Okay. Could you please describe your duties and responsibilities? MR. TURNER: Okay. I deal with requirements and compliance and focusing mainly on FAA and JAA rulemaking for type certification and operation of commercial-type aircraft. MR. BERMAN: Okay. And please describe your education and training and prior experience that qualified you for this position. MR. TURNER: I graduated from Georgia Tech in 1966, and I've been working with the Douglas Company and McDonnell Douglas and Boeing ever since. I've worked primarily in the Aircraft Performance Group. I've worked on the DC-8, DC-9, DC-10, and MD- 80 aircraft. I was the Performance Group Manager for the MD-11 and MD-90 before my present position. MR. BERMAN: Okay. Thank you. And do you have any FAA airman certificates or others? MR. TURNER: No. MR. BERMAN: Okay. Thank you, sir. Go ahead, Mr. Pereira. MR. PEREIRA: Thank you, Mr. Berman. INTERVIEW BY TECHNICAL PANEL MR. PEREIRA: Mr. Gilleran, Mr. Turner, and Mr. Melody, I understand you have presentations on the subjects of MD-80 spoiler and auto brake systems, landing performance, and flight operations with respect to this accident. Mr. Chairman, these subjects are all closely related. So, I'd prefer that the presentations be given sequentially with all questions held until after the last presentation. CHAIRMAN HALL: I'll try to restrain myself. Please proceed. MR. PEREIRA: Okay. The Boeing staff can proceed with their presentation. MR. GILLERAN: Yes. May I have the first slide, please? Let me begin by saying, first of all, thank you on behalf of the Boeing Company and all of my colleagues, both here and back at the Long Beach facility, who have worked hard on this investigation. I want to say that we clearly recognize the importance and the value of this hearing, and we are hopeful that our participation can lead to an improvement in air travel safety. Per the Board's request, our testimony today will concentrate on three aspects of the MD-80 aircraft. I will present a technical description of the spoiler and auto brake systems. Mr. Turner will focus on the measured stop performance and the effects of wet runway and lack of spoilers on the MD-80 stop distance, and Captain Melody will provide a presentation on the recommended operating procedures of the MD-80 aircraft. Again, I will provide details on the MD-80 spoiler systems, speed brake and ground spoiler functions, and how the auto spoiler system works to interface with the spoiler system ground spoiler function, and, finally, the general arrangement and operation of the auto brake system. The MD-80 has three spoiler panels on each wing. There are two flight spoilers, very weak red mark, but outboard flight spoiler and the inboard flight spoiler and one ground spoiler p