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On March 6, 2001, at 2200 Pacific standard time, an experimental amateur-built RV-6A single engine airplane, N46KA, was substantially damaged when it impacted rising terrain west of Inyokern, California. The airline transport pilot and pilot-rated passenger both received fatal injuries. The pilot, who was also the builder/owner of the airplane, was operating the airplane as a personal flight under the provisions of 14 CFR Part 91 when the accident occurred. The flight had originated from the Zamperini Field in Torrance, California, about 2100, and was reportedly en route to Bishop, California. Instrument meteorological conditions prevailed in the area and an instrument flight rules (IFR) flight plan had been filed and activated en route.
According to the Federal Aviation Administration (FAA), air traffic controllers at High Desert Terminal Radar Approach Control (TRACON) were contacted by the pilot at 2115:39. The pilot indicated he was flying at 9,500 feet and was en route to Bishop. At 2118:13, the pilot reported he was going to climb to 10,500 feet. At 2139:04, the air traffic controller asked the pilot what the flight conditions were, to which the pilot replied, "we're VFR [visual flight rules]." At 2139:49, the pilot told the controller they were getting into rain and they were going to try to get under it. The pilot asked the controller if they were depicting the weather on the radar. The controller informed the pilot that a band of precipitation was depicted 5 miles north of the aircraft's position and it stretched to the east approximately 50 miles, to the west approximately 20 miles, and to the north it stretched to 20 miles north of Inyokern.
At 2141:16, the pilot told the air traffic controller he had reversed the aircraft's direction and was going to see if he could get below a cloud layer then proceed on course. The controller asked the pilot if he was IFR qualified and equipped, to which the pilot reported he was. The controller offered to give the pilot a vector to Bishop in IFR conditions, and then could attempt to put the aircraft in VFR conditions once the airplane was farther north. The pilot asked how far the precipitation band extended to the north, to which the controller reported 43 miles from the aircraft's current location. The pilot then elected to establish the flight on an IFR flight plan to Bishop, and requested the current weather for their destination.
The air traffic controller then issued a clearance to Bishop via vectors, initiating with a vector heading of 340 degrees, and an altitude of 13,000 feet. The controller then told the pilot that the weather data he had on Bishop was 50 minutes old. The Bishop weather was reported as wind from 290 degrees at 6 knots; visibility 10 statute miles; scattered clouds at 8,000 feet; temperature and dew point 3 degrees Celsius; and an altimeter setting of 30.12 inches of mercury.
At 2146:30, the air traffic controller told the pilot he could assign him a higher altitude if he wanted it. The pilot indicated he would remain at 13,000 feet, but wanted to know if there were any reports of icing. The controller said that there were no pilot reports and that his weather data reported that "the tops [were] around 15,000 feet." The pilot stated that they would stay at 13,000 feet and "should we encounter icing, we'll just ask for a one eighty back to Mojave and go there."
At 2153:56, the controller told the pilot they had passed through the worst of the depicted precipitation and the pilot had another 20 miles to get past the remaining precipitation. The pilot responded at 2154:09, by stating, "at our altitude, it looks like snow out there." At 2155:28, the pilot told the controller he was experiencing a rough running engine and they wanted to divert to Inyokern. He requested the weather information for Inyokern. The air traffic controller stated that he did not have weather information for Inyokern; however, he had the weather data for China Lake (China Lake Naval Air Weapons Station (NAWS) Armitage Field, which is located approximately 7 miles east of Inyokern). The pilot requested a vector to China Lake. The controller told him to fly a heading of 090 degrees and gave the pilot the China Lake weather, which was wind from 180 degrees at 5 knots; visibility 6 statute miles with rain and mist; few clouds at 2,500 feet; broken ceiling at 2,900 feet; and an overcast ceiling at 4,300 feet. The controller added, "[it] doesn't look very good, I suggest Mohave."
At 2156:21, the pilot then indicated they would not make it to Mohave, told the controller they had to divert to China Lake, and declared an emergency. The controller issued a vector heading of 075 degrees to the China Lake Airport, and told the pilot that the airplane was 16 miles west of the airport. At 2157:52, the air traffic controller informed the pilot the minimum vectoring altitude (MVA) for the aircraft's location was 10,500 feet, and the MVA would be lower in approximately 7 miles. At 2158:24, the pilot indicated he needed a "vector away from terrain." The controller told the pilot to maintain his present heading and that would take them to the lowest terrain in the area. The pilot asked for the current weather information at China Lake, to which the air traffic controller replied, "weather is 6 miles and rain and . . . low ceilings, 2,900 broken, 4,300 overcast."
At 2159:02, the pilot asked the controller, "what's the terrain in this area where I am now?" The controller told the pilot they were clearing the higher terrain, and should be approaching a highway. The controller added they were approximately 3 miles west of the Inyokern Airport. At 2159:39, the pilot asked what the terrain was like at their current position and informed the controller they were descending through 5,000 feet. The controller informed the pilot his present heading would take him to the best terrain conditions. At 2200:07, the controller lost radar contact with the accident airplane.
The last radar return indicated that the airplane was located about 3 miles west of Inyokern with a mode C altitude report of 4,700 feet msl. The airplane's last known position was 35 degrees 38.16 minutes north latitude and 117 degrees 54.31 minutes west longitude.
The pilot was employed as a commercial airline pilot. He held an airline transport pilot certificate for single and multiengine land airplanes, and was issued a first-class medical certificate on October 4, 2000, with a limitation to have glasses available for near vision. According to his employer, he completed his last airmen flight check on September 19, 2000. They also reported he had accumulated approximately 6,644 total flight hours. Using aircraft records, NTSB investigators estimated that the pilot had accumulated at least 216 hours in the accident airplane.
The pilot was the owner and builder of the experimental amateur-built airplane. Review of the aircraft records revealed the pilot began building the airplane on November 1, 1997, and completed its construction on November 26, 1998. On December 26, 1998, the aircraft was issued a Special Airworthiness Certificate. The airplane underwent a pitot/static and transponder systems check on February 28, 1999. On February 6, 2001, the airplane underwent its last condition inspection and was found to be "in a condition for safe operation." The pilot/owner was the person who endorsed the last condition inspection.
The aircraft was equipped with an Apollo GX65 Global Positioning System (GPS).
The aircraft was equipped with a Lycoming O-360-A1A carbureted engine. Van's Aircraft, Inc., the aircraft kit manufacturer, provides a Filtered Air Box Kit (FAB-360). According to Van's Aircraft, the induction air box was designed to provide a uniform, low restriction air induction. It incorporates a small, low external drag, high inlet velocity opening with an efficient pressure recovery plenum area around a circular air filter. The air plenum and circular air filter provide a uniform airflow into the carburetor venturi, and thus a uniform, balanced flow distribution through the induction manifold to the respective cylinders of the engine.
The air box design includes a pilot-actuated alternate air door for simultaneously blocking off outside inlet air and opening an alternate heated air source. The alternate air source can be either heated air directly from the warm air plenum of the lower engine compartment, or from an exhaust manifold heat muff, at the discretion of the aircraft manufacturer (builder). This design permits the pilot to supply either outside ram/pressure recovery air to the carburetor, or to completely block the outside ram air and instead supply heated air from inside the engine cowling, or from an exhaust stack heat muff, to the carburetor. The heated air is ducted to the front side (upstream) of the air filter.
Review of photographs taken at the accident site revealed that the accident aircraft had a carburetor air box similar to the kit sold by Van's Aircraft installed. However, it is not known as to what method of heated alternate air source and routing was utilized by the builder.
The pilot obtained a standard weather briefing at 1929, from the Hawthorne Flight Service Station (FSS). According to the printed transcripts of that briefing, the pilot requested a standard weather briefing from Torrance to Bishop. The weather briefer asked if the pilot was planning to fly IFR, to which the pilot replied in the affirmative. The pilot indicated he was planning on flying at 7,500 feet, and the flight would take approximately 1 hour 30 minutes. He reported he would depart around 2030.
The weather briefer informed the pilot there were flight precautions in effect for the entire route of flight, which carried the potential for occasional moderate rime or mixed icing in the clouds and precipitation. The freezing level was reported as 7,000 feet up to 20,000 feet for the entire route. The briefer also reported that moderate turbulence was possible below 15,000 feet, especially in the vicinity of rough terrain. He added that there was the potential for mountain obscurement by clouds, occasional precipitation, and isolated thunderstorms. VFR flight was not recommended.
The pilot was informed of a low pressure system off the coast of California that was resulting in "bands of moisture and instability" and "some significant convection over . . . California low and high deserts . . ." The current weather for Torrance was given as wind from 140 degrees at 8 knots; visibility 25 statute miles; scattered clouds at 1,500 feet agl; broken clouds at 20,000 feet; temperature 13 degrees Celsius; dew point 10 degrees; and an altimeter setting of 29.90 inches of mercury.
The weather briefer then informed the pilot the basin area was drying out and there were scattered clouds around 2,000 - 4,000 feet. He added as the flight approached the mountains, the pilot could expect higher broken layers that were occasionally overcast with bases between 5,000 and 7,000 feet, and higher layers at 10,000 feet. The briefer reported the "layers are occasionally merging and extending up above 20,000 feet."
The weather briefer reported the visibilities along the route were 7 statute miles or better with isolated thunderstorm activity up over the Palmdale, Edwards area, and northward into the Owens Valley area. The briefer stated the weather radar over the intended route of flight depicted wide spread and widely scattered light rain and scattered imbedded moderate cell tops to flight level 300. He added the "active weather is drifting towards the Palmdale, Lancaster area then back out towards the coast, so it's going to continue to impact that area probably at least overnight."
The weather briefer then issued the current weather at Bishop, which was reported as wind from 300 degrees at 6 knots; visibility 10 statute miles; few clouds at 3,400 feet; scattered clouds at 7,000 feet, and an overcast cloud layer at 10,000 feet; temperature 4 degrees Celsius; dew point 3 degrees Celsius; and an altimeter setting 30.10 inches of mercury. He added that a thunderstorm was reported at 17 miles north of Edwards, and it was moving north-northwest.
The pilot was informed that the forecast for the route held little significant change until daybreak the following morning. The route forecast predicated scattered clouds between 3,000 and 4,000 feet, broken clouds between 6,000 and 7,000 feet, and scattered and broken layers to 20,000 feet. The weather briefer told the pilot the forecast visibilities held the potential for 5 statute miles in light rain, showers, and mist. Isolated thunderstorms and light rain showers were forecast through the mountains with the mountains becoming occasionally obscured. The briefer also reported the forecast, until 2200, included visibilities more than 6 statute miles with light rain and broken ceilings at 5,000 feet and areas of broken ceilings at 2,000 feet.
The weather briefer also informed the pilot that local visibilities (for the Palmdale, Inyokern, and Bishop area) were forecast as 1/2 statute mile in snow with overcast ceilings at 500 feet, isolated surface wind gusts to 30 knots, with occasional visibilities of 3 statute miles in thunderstorms, moderate rain, small hail, and mountain obscurement.
The pilot was informed conditions were forecast to improve somewhat to locally IFR and marginal VFR conditions after 2200; however, the weather was still forecast until 0200, to be scattered to broken clouds at 9,000 feet with occasional scattered light rain showers, ceilings broken at 4,000 feet and possibly 1,000 feet, with visibilities of 1 statute mile in light snow showers.
The terminal forecast for Bishop until 2300, was reported as wind from 010 degrees at 9 knots; visibility more than 6 statute miles in light rain; scattered clouds at 1,500 feet; overcast clouds at 4,000 feet; and occasional visibilities of 5 statute miles in light rain and mist with an overcast ceiling of 1,500 feet.
The pilot was issued the winds aloft information and was informed again that the freezing level was at the 7,000- to 7,500-foot level. The weather briefer provided the notices to airmen and requested a pilot report if the pilot had time. The pilot asked the weather briefer if his radar data was depicting any precipitation, to which the briefer replied, "no, right now north." The pilot asked if there was any in the valley, to which the briefer replied, "looks like some creeping in from the southeast maybe 20 to 30 miles north of Edwards." The controller added that the precipitation was heavier west of Edwards, where it met the southern Sierras.
The pilot indicated that they would "talk it over and see what we're going to do," and ended the briefing.
The Safety Board conducted a meteorology study. The following are details extracted from that study:
The closest weather observation facility was located at the Kern County Airport (IYK), Inyokern, which was 5.5 miles east of the accident site at an elevation of 2,455 feet msl. At 2047, which was the last observation of the day, the weather was reported as winds from 360 degrees at 15 knots; visibility 20 statute miles in light rain; few clouds at 4,000 feet; overcast ceiling at 8,000 feet; temperature of 10 degrees Celsius; and an altimeter setting of 30.02 inches of mercury.
At 2138, the weather observation facility at China Lake NAF reported the following special weather report: wind from 180 degrees at 5 knots; visibility 6 statute miles in moderate rain and mist; few clouds at 2,500 feet; ceiling broken at 2,900 feet; overcast clouds at 4,300 feet; temperature and dew point missing; and altimeter setting of 30.06 inches of mercury.
Review of the closest upper air soundings (108 miles northeast of the accident site) depicted a freezing level of 7,841 feet.
The local weather radar data could not be retrieved, therefore, the National Radar Mosaic was utilized to determine if there were any significant radar echoes over the region surrounding the time of the accident. At 2200, the radar image depicts a range of light to moderate precipitation over the region.
The Geostationary Operational Environmental Satellite number 10 (GOES-10) infrared imagery was obtained from the National Weather Service. At 2000, the GOES-10 infrared image depicted a westward movement of a cloud band over the accident site. The radiative temperature over the accident site corresponded to cloud tops in the 22,000-foot range.
In-flight weather advisories AIRMET Sierra, Zulu, and Tango for were valid for mountain obscuration, icing conditions, and moderate turbulence, respectively, during the time and over the location of the accident. AIRMET Zulu advised that moderate rime and mixed icing were possible in clouds and precipitation between the freezing level and 20,000 feet. The freezing level was identified between 6,500 feet to 7,500 feet over California.
Four pilot reports were issued between 1655 and 1930, indicated that moderate turbulence and light to moderate rime ice were present over Edwards, Bakersfield, and Palmdale between 8,000 and 20,000 feet. At 2232, (32 minutes after the accident) the pilot of a Beechraft commuter turboprop aircraft at 9,000 feet reported a temperature of -2 degrees Celsius and light to moderate rime icing over Bakersfield, California, (54 miles west of the accident site).
The National Center for Atmospheric Research (NCAR) were contacted because of their work in the field of icing research and their icing diagnostic program, which is used to determine the threat of airframe icing and Supercooled Large Droplets (SLD). The NCAR Integrated Icing Diagnostic Algorithm (IIDA) model was utilized to identify the 3-dimensional extent of the clouds. The IIDA model then uses information from numerous resources (PIREPS, satellite imagery, radar data, etc.) to identify the locations and likelihood of both conventional and SLD icing across the United States and Canada. The IIDA forecast indicated a low probability for icing associated with SLD for 2000, on March 6, 2001. However, the potential for icing over the Inyokern area was greater than 90 percent. The icing layer was defined with a base between 5,000 and 7,500 feet with tops to 15,000 feet. The probability of icing at 9,000 feet and 12,000 feet was greater than 70 percent over the region of the accident.
The cross section of icing indicated that the icing potential was increased in altitude as the airplane approached the Palmdale, Edwards, and Inyokern area, with 90-100 percent probability of icing between 8,000 and 11,000 feet. The maximum vertical extent of the icing was over the Inyokern area.
The China Lake NAF weather observation facility reported a temperature and dew point of approximately 46 degrees during the 2156 observation. According to the FAA's Carburetor Icing Probability Chart, with these conditions, there was a high probability of serious icing under cruise power settings.
Astronomical data was obtained from the U.S. Naval Observatory for the accident site location. Sunset occurred at 1757, and the end of civil twilight was at 1822.
WRECKAGE AND IMPACT INFORMATION
Upon their arrival in the search area, a helicopter crew from the Kern County Sheriff's Office visually located the airplane at 0830 on March 7, 2001. Deputies reported the accident site was located at 35 degrees 38.28 minutes north latitude and 117 degrees 55.91 minutes west longitude on a 59-degree magnetic bearing to China Lake. Terrain elevation at the site was estimated by investigators to be about 4,700 feet msl. The wreckage was examined on-scene by FAA inspectors and a Lycoming engine air safety investigator.
FAA inspectors at the accident site reported the airplane struck 30-degree rising terrain while on a heading of about 070 degrees. The ground scars extended from the initial point of impact for about 80 feet upslope until reaching the airplane's point of rest. The airplane came to a final resting heading of 150 degrees. All flight controls were in place and attached at the accident site and there was no evidence of any in-flight structural separation. The airplane came to rest with all major components attached. The wing leading edges, cockpit/cabin area, and the rudder sustained impact damage. The damage sustained by the engine and cockpit was up and aft crushing. Structural deformation was nearly uniform along the leading edges of both wings. Both fuel tanks showed evidence of hydraulic deformation. Bulging and tearing of the tanks was evident at the leading edge of each wing.
The engine remained attached to the fuselage; however, the propeller separated from the engine crankshaft just aft of the propeller mounting flange. The propeller was found laying on the ground approximately 30 feet from the aircraft. The crankshaft fracture surfaces displayed 45-degree shear lips. Both propeller blades were twisted toward a lower pitch angle and one propeller blade was twisted approximately 180 degrees about midway through its length. One propeller blade displayed significant leading edge gouging, and chordwise scoring and paint was removed from the face of the blade. The other blade displayed lighter chordwise scoring and leading edge gouging.
Photographs taken at the accident site indicated that the airspeed indicator needle was trapped at 180 knots (the indicated never exceed speed). The face of the altimeter was found with 30.18 inches of mercury displayed in the Kolesman window. The altimeter's indicating needles were not located. The vertical speed indicator face was located with the indicating needle still attached. The needle was found pointing to a 1,700-foot/minute descent rate.
The carburetor heat control knob, which was located to the right of the throttle control was found in the in (or off) position; however, that area of the cockpit sustained extensive aft crushing.
The wreckage was transported to a storage facility in Compton, California, where the engine was examined on March 8, 2001, in further detail under the supervision of a Safety Board investigator.
The alternator and starter were separated from their mounting pads located on the bottom of the engine. The top spark plugs were removed and examined. When compared to the Champion Spark Plugs Check-A-Plug chart AV-27, the spark plug electrodes displayed coloration consistent with operation with a rich fuel/air mixture. The vacuum pump was removed, and the crankshaft was rotated by hand through the drive pad utilizing a drive tool. The crankshaft rotated freely in both directions and thumb compression and valve operation was confirmed on all four cylinders. The cylinder combustion chambers were examined through the spark plug holes utilizing a lighted bore scope. The combustion chambers were unremarkable, and the gas path and combustion signatures observed at the spark plugs, combustion chambers, and exhaust components were consistent with a rich fuel/air mixture.
The engine ignition system was equipped with a Unison Industries Limited Authority Spark Advance Regulator (LASAR). The unit was found securely attached at the firewall mounting, with the attached harness assemblies secure to their respective connector. The left magneto was found securely clamped at its mounting pad. The magneto was removed and would not produce a spark at its leads during hand rotation of the magneto drive. The right magneto was found secured at its mounting pad. The magneto was removed and produced a spark at its leads when its drive was manually rotated.
The carburetor was separated from the engine, but remained attached to the throttle and mixture controls. The throttle butterfly valve was found in the full open position. All engine compartment fuel lines were found in place and secured, and the carburetor's fuel inlet screen was found free of contamination. The carburetor was disassembled and no internal malfunctions or defects were noted. The fuel pump was attached to the engine at its mounting pad. It was removed for examination and was found free of internal contamination and malfunction.
Both intake and exhaust manifolds were examined an found free of obstructions, with the exception of dirt, similar to that at the accident site, located in the intake manifold and carburetor venturi. The carburetor air box and filter were crushed.
TESTS AND RESEARCH
The GPS unit was shipped to a repair facility in an attempt to download non-volatile information concerning the accident flight. According to the repair facility, the only retrievable information was its last recorded position (35 degrees 38.31 minutes north latitude and 117 degrees 55.94 minutes west longitude), the nearest waypoint (IYK 5.2 nautical miles on a 062-degree bearing), and the primary and secondary radio communication frequencies.
Toxicological tests were conducted on both the pilot and the pilot-rated passenger. Tests for carbon monoxide, cyanide, volatiles, and drugs were negative for both pilots.
According to the FAA Flight Training Handbook (AC 61-21A), "the pilot should apply carburetor heat whenever conditions are conducive to icing."