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On March 26, 1997, approximately 1010 mountain standard time, a Cessna 172P, N97527, registered to and being operated by Brentco Aerial Patrol, Inc., and being flown by a commercial pilot, was destroyed during impact with terrain following a loss of control in flight approximately 11 nautical miles (nm) south-southwest of Burlington, Wyoming. The pilot was fatally injured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was an aerial pipeline patrol, was to have been operated under 14CFR91, and originated from Worland, Wyoming, approximately 0950.
According to personnel stations at the operator's base at Durango, Colorado, the pilot departed Bridger, Montana, where he based the aircraft, and commenced an aerial pipeline patrol flight sometime early on the morning of Wednesday, March 26, 1997. Several credit card receipts were found showing fuel purchased at the fixed base operator at the Worland, Wyoming airport. These receipts provided the following information:
Monday (03/24/97) 07:48AM 28.6 gallons 100LL avgas Tuesday (03/25/97) 10:18AM 39.0 gallons 100LL avgas Wednesday (03/26/97) 09:48AM 34.7 gallons 100LL avgas
The fueler at the Worland airport reported that he was accustomed to seeing N97527 stop for fuel. He also reported that on the morning of Wednesday, March 26, he topped off the wing fuel tanks after which the aircraft immediately departed (note the time of the credit card transaction shown at 0948).
The operator reported that the pilot was contractually required to patrol each of the designated pipeline routes a minimum of once per week. The pilot was given flexibility as to when to conduct the various patrol flights and in what order.
The aircraft's emergency locator transmitter (ELT) operated subsequent to the accident and signals were reported to Seattle Air Route Traffic Control Center at 1135. The aircraft was subsequently visually located at 1544.
The aircraft was found at a point 32 nm west-northwest of the Worland airport, and on a direct line toward the Cody airport (refer to CHART I). Documentation found at the crash site showed a series of patrol routes, of which one was observed to begin at a point named Silver Tip (arrow A on CHART I) and continue southeast past the Worland airport and thence southwest and west to a point named Gooseberry (refer to CHART I). An intermediate point on this route named Slick Creek was observed to lie just east of the Worland airport (refer to arrow B on CHART I, and CHART II). Additionally, a separate portion of this route was observed to begin just east of the Cody airport at Cody Booster (refer to arrow C on CHART I, and CHART II) and terminate approximately 10 nm southeast of the airport at Oregon Basin (refer to CHART II). This termination point was approximately 25 nm north of Gooseberry (refer to ATTTACHMENT I which names the patrol route points for the entire route).
No pilot logbooks were located and the flight time entered into the core report were provided by the Operator. The pilot was hired by the Operator on February 6, 1996, and began flying pipeline patrol flights in the Southwest (Texas-New Mexico) shortly thereafter. He was transferred to pipeline routes in Wyoming on January 29, 1997, and moved to Bridger, Montana (refer to CHART I).
N97527 was, according to the Operator, assigned to the pilot after he was hired. According to the airframe log, the aircraft accrued approximately 1,109 hours for flight time between February 18, 1996, and the date of the accident.
N97527, a Cessna 172P, was equipped with two 27 gallon metal fuel tanks, one located in each wing root area. Or the 27 gallons available in each tank, all but 2 gallons were usable. The fuel is fed by gravity from the wing tanks through a four position selector valve and on to the carburetor. The selector valve positions are (from the 6 o'clock position clockwise) OFF, LEFT, BOTH, and RIGHT.
Additionally, the aircraft had been modified per Supplemental Type Certificate SA615NE, dated 10/18/88, to include an 18 gallon aft baggage compartment fuel tank. The aluminum tank was serviced through a filler port on the right side of the fuselage (refer to photograph 4). Fuel within the tank was transferred via an electric pump into the right wing tank. The tank was equipped with both a sump drain and vent line.
The transfer pump was operated via a control panel located immediately aft of the fuel selector valve on the floor of the cockpit and between the front seats. The control panel was equipped with a round, analog fuel gauge located in the center with marked positions showing "E" (empty), "1/2" and "F" (full). A three position switch controlling the electric pump was located to the left of the gauge and a single, small incandescent light was located to the right of the gauge.
The axis of the toggle switch, which in its mid position, was normally parallel to the aircraft's vertical axis, could be moved aft to the OFF position, or forward to the START position. THE START (forward) position was spring loaded such that the switch, when released, would return to the mid position, marked RUN. The OFF (aft) position was not spring loaded (refer to photograph 19).
Operating procedures for the fuel transfer system were to:
1. "Operate on main tanks until right fuel gauge reads 2/3 full." 2. "Move transfer switch to momentary position and hold for 10 seconds. Light should illuminate and remain illuminated when switch is released." 3. "If light does not stay illuminated, repeat step 2." 4. "Transfer while operating on right main tank in straight and level flight only." 5. "Transfer is in progress when transfer light is illuminated." (refer to ATTACHMENT M pages 1-4)
The aviation surface weather observation taken at Cody, Wyoming at 0855 on the morning of the accident reported winds from 220 degrees magnetic at 13 knots with gusts to 17 knots. One hour later (0955) the station reported winds from 260 degrees magnetic at 13 knots with gusts of unreported intensity.
The aviation surface weather observation taken at Worland, Wyoming, at 0855 on the morning of the accident reported winds from 310 degrees magnetic at 3 knots. One hour later (0958) the station reported winds from 300 degrees magnetic at 3 knots. Winds remained light throughout the day with no gusts reported.
WRECKAGE AND IMPACT INFORMATION
The ground impact site was established at 44 degrees 17.078 minutes north and 108 degrees 33.262 minutes west latitude and longitude respectively using a hand held global positioning unit. The elevation of the site was approximately 5,850 feet above mean sea level. The terrain at the site was characterized by uneven, sage covered terrain with numerous moderate slope changes (refer to CHART III).
According to personnel responding from the Big Horn County Sheriff's office, the aircraft was observed by search and rescue personnel at the accident site in a nose low, nearly vertical attitude with respect to the terrain. During the night following the accident strong winds reportedly blew the aircraft over onto its back.
The investigative team observed the aircraft in an inverted attitude with the longitudinal axis oriented along a 091/271 degree magnetic bearing line (tail east). The slope at the initial impact site was measured at -35 degrees towards the east-northeast. The crush along the underside of the aircraft's engine/forward fuselage was measured to be approximately 27 degrees. The left wing was observed to be displaced aft somewhat of the aircraft's lateral axis, whereas the right wing was displaced forward to the same approximate degree. The left main landing gear displayed greater aftward deformation compared to the right main landing gear. The auxiliary fuel tank cap was observed hanging loose by its attach cable. No paint abrasions, scarring, or fuel stains were observed in the vicinity of the auxiliary fuel filler port (refer to photographs 1 through 5 and CHART III).
All of the aircraft (control surfaces, powerplant and airframe) was located at the crash site. Additionally, there was no evidence of any discontinuity within any of the three flight control systems, nor between the throttle and mixture control cables and the carburetor.
The initial ground impact site was observed several feet west of the final resting place of the aircraft's engine (refer to photograph 5). A faint ground impact impression was observed oriented along a 166 degree magnetic bearing line. This impression extended from an area approximately 20 feet from the center of the initial ground impact site north, and small fragments of red wingtip navigation lens and plastic wingtip fragments were noted at its terminus (refer to photograph 6). The initial ground impact site was also characterized by three prominent impact depressions, the largest of which was a crater containing small engine and plastic nose cowl fragments. Upslope to the west and roughly equidistant from this crater were two smaller impact craters containing fragments associated with the left and right wheel fairings. Numerous large pieces of forward cockpit windscreen were observed lying on the ground at this site (refer to photograph 7).
The left wind strut was buckled somewhat near the fuselage. The wing was observed to be twisted approximately 30 degrees (leading edge up) at the tip, and the wing was deformed upwards approximately 36 inches progressing from root to tip. The flap was observed to be partially extended. Additionally, the tip cap was absent, there was noticeable aftward accordion like deformation at the leading edge, and a distinctive "bulge" deformation was noted on the underside in the vicinity of the fuel tank consistent with a hydraulic impact effect from an impact of a fuel tank containing substantial fuel (refer to photograph 8).
The right wing strut was buckled near its midpoint. The wing was observed to be deformed upwards from mid-span towards the tip. The flap was observed to be partially extended. Additionally, the tip cap was in place, there was little aftward accordion like deformation at the leading edge, and the distinctive "bulge" deformation was noted on the underside in the vicinity of the fuel tank consistent with a hydraulic impact effect from an impact of a fuel tank continuing substantial fuel (refer to photograph 9).
The engine was observed to have been displaced aftward into the forward cockpit area. The propeller remained attached and one blade displayed aftward bending deformation of approximately 80 degrees. This blade also displayed light leading edge abrasion of paint, minimal chordwise scratching and multiple abrasions of the white tip paint along a line perpendicular to the chord line (refer to photograph 10). The opposing blade displayed only a few degrees of aftward bending deformation along with light leading edge abrasion of paint and minimal chordwise scratching (refer to photograph 11).
A blue stain characteristic of 100 low lead aviation fuel was observed at the leading edge of the right wing (low point) emanating from the wing strut attach point outboard towards the tip (refer to photograph 12).
The empennage, vertical and horizontal stabilizers, and their associated control surfaces, sustained minimal damage. The plastic cap at the top of the vertical stabilizer was observed to be broken. The left horizontal stabilizer displayed light upwards bending deformation mid span (refer to photograph 13). The right horizontal stabilizer was undamaged and the elevator trim tab was observed to be positioned approximately 15 degrees tab up (refer to photograph 14).
Additionally, the aircraft's mechanical clock was observed to have stopped at 10:09:30. The fuel selector within the cockpit was observed midway between "BOTH" and "RIGHT" tanks, and the auxiliary transfer pump switch was observed in the "RUN" position with the associated fuel gauge reading just under one-half tank. Approximately 1-2 ounces of blue aviation fuel were drained from the line connecting the gascolator to the carburetor with trace amounts of fuel within the carburetor. The aircraft's electrically driven flap jackscrew unit was examined and fount to be extended to a position corresponding to 8 degrees of flap extension. The magneto switch was observed in the "LEFT" position. The tachometer hour meter was observed to read 84.81 hours.
A spiral bound notebook clipped open to a specific page was found at the accident site. The notebook contained a series of hand written notes consisting of alpha numeric characters with numbers beneath them. The first and last of the three references were annotated "WRL" which is the three letter identifier for the Worland, Wyoming airport. The intermediate reference was annotated "7V6" which is the identifier for the Guernsey, Wyoming airport, where the aircraft had fueled on March 25, 1997. The number beneath 7V6 was 79.9 and the number beneath the WRL entry was 84.4.
MEDICAL AND PATHOLOGICAL INFORMATION
Post mortem examination of the pilot was conducted at the Michelotti Sawyer's Nordquist mortuary, Billings, Montana, on the afternoon of March 27, 1997. Toxicological evaluation of samples taken from the pilot was conducted by the FAA's Toxicology and Accident Research Laboratory. All findings were negative (refer to attached Toxicology report).
TEST AND RESEARCH
The aircraft was re-examined at the facilities of Arlin's Aircraft Services, Bozeman, Montana, on April 16 and 17, 1997. The following areas and associated results were as follows:
The aircraft's ignition switch was checked and found free of any electrical discontinuity. Likewise, both magnetos were checked and found to be capable of producing a spark at each of their four leads. The timing was found to be 26-27 degrees before top dead center for the left magneto and 25 degrees before top dead center for the right magneto. All eight spark plugs were examined. The top plugs for numbers two and four cylinders displayed an oil coating. The remaining six plugs displayed a gray coloration with no evidence of excessive wear or improper gapping. The airframe fuel vent system was examined and no discrepancies were found. Additionally, the vent check valve was tested and found to be unblocked.
The Lycoming O-302-D2J was examined and then disassembled. Continuity of both the crank and cam shafts, as well as appropriate rocker arm movement, was verified as was compression on each cylinder. A small amount of metal contamination was found within the oil suction screen. The oil filter, which had several small magnets affixed to its external canister, was cut open and examined and found to contain very small slivers of metal. The engine case was split and the pistons, pins crankshaft, cam shaft, bearings and connecting rods and valve tappets were examined. The only discrepancy noted was a wear down of approximately 7/32 of an inch on two of the cam shaft lobes, and spalling of the tappet face on the four associated tappets (refer to photographs 15 and 16).
The carburetor, which had broken free of the engine, was examined. The throttle and mixture control cables remained attached and the throttle setting was observed to be approximately 3/4 open, while the mixture arm was observed in the mid-range position. Examination of the gascolator bowl revealed less that one-half ounce of water and a small amount of corrosion and sediment at the bottom of the bowl. The carburetor heat valve was observed in the closed (cold) position. The carburetor housing was free of crushing deformation (refer to photograph 17). The housing was opened and the internal mechanics of the carburetor were examined. There was no evidence of any mechanical malfunction within the carburetor, however, one of the floats was observed to have implosive type "hydraulic" deformation (refer to photograph 18).
The auxiliary fuel transfer system was removed from the aircraft, examined and tested. The spring loaded switch was found to function normally as did the transfer light when a replacement bulb was inserted in place of the shattered bulb (refer to photograph 19). A container of cleaning solvent was used as a fluid source and the pump system was tested using an aircraft battery. After several seconds of priming with the switch in the START position, the transfer light burned steady and fluid flowed at a rate of 0.321 gallons per minute at 1 pound per square inch pressure (psi). When the outflow line from the pump was blocked fluid flow ceased and the pressure rose to 4.4 psi.
A telephone conversation with an engineer on the staff of Textron Lycoming revealed that the acceptable flow rate of fuel to the Facet MA-4 SPA carburetor for the O-320-D2J engine ranged from a minimum of 0.5 to a maximum of 8.0 psi.
The test run of one of the Operator's Cessna 172 aircraft equipped with a Lycoming O-320-H2AD engine and 18 gallon auxiliary fuel system was conducted on February 20, 1998. The test was conducted at approximately 3,000 feet above sea level with the engine operating at 2400-2450 RPM. The left and right wing fuel tanks had been filled and, subsequent to engine start, and with the engine drawing fuel from the left tank, the auxiliary fuel transfer pump was activated. The aircraft was operated for a period of approximately 45 minutes with the intent of transferring fuel from the auxiliary tank into the right tank and with the left tank selected for the duration. When the right tank was unable to accept any additional fuel, and with a head pressure from the auxiliary transfer pump, fuel was expected to begin transferring into the left tank via the tank vent interconnect line (refer to DIAGRAM I). When the left tank was unable to accept any additional fuel, the fuel was then expected to pressurize the spring loaded vent line value to the closed position. The test was to determine, if at this point, the fuel within the pressurized fuel system would then transfer entirely to the carburetor at such a rate as to flood the engine. The test resulted in a continuously running engine with no degradation or loss of power. The auxiliary transfer pump light was observed "ON" for the duration of the flight and approximately 11 gallons of fuel was transferred out of the tank by the end of the flight. The left and right wing tanks remained full upon landing. The pilot reported that he was accustomed to seeing the auxiliary transfer system move all 18 gallons of fuel out of the tank in approximately one hour's time (0.30 gallons per minute flow rate). Subsequent to the flight test, the aircraft was inspected with no evidence of any fuel leaks.
On site examination of the wreckage was conducted on the afternoon of March 27th and the wreckage, which remained at the site, was verbally released on a conditional basis for removal only to Mr. Chuck Carstensen, representative of AVEMCO. Itemized aircraft logs and records as well as associated paperwork found at the site by the Big Horn County Sheriff's Department in a brown leather navigation bag were retained by the IIC. Original pipeline route maps (red binder, manila folder, and stapled topographic charts were copied and the originals were sent via US Overnight Mail to Mr. Rick Vincent, in care of Marathon Pipeline, Powell, Wyoming, on Saturday afternoon, March 29th.
The wreckage was released to Mr. Carstensen subsequent to the engine and airframe examination, and written wreckage release was documented on NTSB form 6120.15 (attached). All retained records, logs and paperwork were returned to Brentco Aerial patrol via Federal Express on August 25, 1997, and some incidental paperwork was returned on February 18, 1998.