WPR16LA110

A loss of engine power for reasons that could not be determined based on the available information.

The commercial pilot and a colleague constructed the single-place, composite airplane with the intention of using it for air racing purposes. Rather than using the single piston engine and propeller specified by the original plans, they opted to power the airplane with two turbojet engines. The engines were designed and intended for use only on model aircraft and were mounted one per side on the lower fuselage, just aft of the cockpit. The airplane was in the very early stages of its flight test program and had flown only two previous flights with an accumulated total flight time of about 0.8 hours. The purpose of the accident flight was to begin exploring the crosswind handling characteristics and capabilities of the airplane. About 200 ft above ground level (agl) during the first landing approach, the pilot conducted a go-around and climbed to pattern altitude for another approach. While in the landing flare about 10 ft agl, a gust of wind from the right side disturbed the airplane, and the pilot applied power to go around. He heard one engine "spool down" and confirmed a power loss on the left engine via the instrument indications. The wind gust and power loss caused the airplane to track left toward an array of unused airliners stored at the airport. Since the airplane's single-engine minimum control speed had not yet been determined, preflight planning called for reducing power on the remaining engine and landing in the event of an engine power loss; however, the pilot maintained about 30-40% thrust on the right engine to avoid impacting one of the airliners. The asymmetric thrust resulted in a loss of directional control, and the airplane was destroyed when it struck a wooden office trailer and the ground. There was insufficient evidence to determine the reason(s) for the loss of engine power, and none of the three most likely causes (fuel flow interruption, air flow interruption, or flameout due to rapid and large throttle input) could be definitively ruled out.

MHV was situated at an altitude of about 2,800 feet msl. It was equipped with three runways, as follows: - Runway 4/22: 4,746 by 60 feet - Runway 8/26: 7,049 by 100 feet - Runway 12/30: 12,503 by 200 feet The runways were arranged so that the thresholds of 4 and 8 were essentially collocated, and that apex was situated about 4,000 feet south-southwest of the threshold of runway 12. Numerous stored/unused airliners were parked east of runway 12, between the centerlines or extended centerlines of runways 4 and 8. Pilot's Helmet The pilot reported that during the flight and accident, he was wearing his Gentex brand model HGU-68 helmet. The Gentex website indicated that the helmet "was designed to meet the rigorous requirements of the U.S. Navy and Marine Corps" and is equipped "with a single visor system qualified at 600 KEAS (Knots Equivalent Air Speed) in accordance with MIL-H-85047A." The pilot reported that the visor was down at the time of the accident, but that the visor opened during the accident sequence, and the pilot sustained a black eye. In a written communication to the NTSB, the pilot stated that his "natural flinch" position was to turn his head slightly to the right, which resulted in the helmet visor friction knob, located on the left side of the helmet, being in a more forward-facing position. He noted that "something in the crash caught the friction knob (there are marks on the knob and the visor is cracked right there) and pulled it open, presenting my eye to the crash." Potential Engine Power Loss Causes Turbine engines can experience significant power losses, or cease operation altogether, primarily due to the disturbance or cessation of the supply of one of the two principle input components, fuel and air. Fuel flow interruptions can be caused by fuel exhaustion, fuel starvation, contaminated or clogged lines or filters, or loss of fuel pressure. Inlet air disruptions are typically the result of disturbed airflow due to atmospheric turbulence, or high sideslip or angle of attack values. Inlet airflow disturbances will often result in compressor stall, where the compressor airfoils exceed their critical angle of attack. Compressor stalls are normally accompanied by loud reports such as "bangs" or a more steady roaring sound. Imbalances between the fuel- and air-flows into the engine can also result in "flameout," where the fuel air mixture in the combustion chamber is either too lean or too rich to support combustion, and the fire in the combustion chamber is extinguished. Such imbalances are most often triggered by rapid and/or large commanded changes to engine thrust levels. In his accident statements to the NTSB, the pilot reported that the left engine lost all power just after he commanded go-around thrust. He reported that he believed that the loss of power was caused by the disturbed or blocked airflow to the engine, due to the gust from the right that prompted the go-around. He did not report any sounds similar to a compressor stall. Pilot-Reported Fuel System Information The pilot provided the following information regarding the fuel system configuration, indications, and post-accident condition: - The fuel tank had an estimated capacity of 7 gallons, including 1 gallon unusable - The fuel tank was situated below the forward front cockpit, under the pilot's legs - The tank quantity was "gauged with a very repeatable float type mechanical fuel gauge on the top of the tank" directly visible to the pilot, on the cockpit floor between his legs - The fuel is routed from the tank to a tee fitting, and then through two shut off valves; the valves were found in the "ON" position at the accident site - Fuel indication just prior to the accident was between 3/8 and 1/2 tank The pilot reported the following planning and operational information - "Bingo" fuel (the quantity at which the testing was to be terminated and the airplane landed) was 1/2 tank - The takeoff fuel quantity was sufficient for 85 minutes of flight when flying the planned test profile. He amplified that value by stating that "That is in economy cruise at 80 mph," and was "based on the L/D check we did on flight one." - He acknowledged that with "Full power on both engines, the duration is much much shorter." - Full power on both engines yields a climb rate of "greater than 2,000 fpm." The pilot provided his estimate of times and power settings for the flight as follows: - The airplane was towed to the runway, and the engine was started at the hold short line - The engine was run for 3 minutes at 20% power to recharge the batteries - Applied full power for takeoff; duration was "1-2 minutes" - Idle descent for 7 minutes. - Conducted an approach to runway 26 down to 500 feet; terminated in go-around - Approximately "20 seconds [at] full power" - Idle descent to runway 12; terminated in accident NTSB Fuel Burn Calculations Using the pilot-reported initial usable fuel quantity of 6 gallons and the OMM maximum fuel burn rate, the two engines could be run for a total of about 9.2 minutes at full throttle. Based on the pilot's estimates, the engines were run for about 17 minutes on the accident flight. Calculations that used the pilot's estimated flight times and power settings, and linear interpolation for fuel burn rate between idle and full thrust, indicated that the flight would have consumed a total of approximately 2 gallons of fuel. Unknowns regarding this aspect of the investigation included the actual pre- or post-flight fuel quantity, the actual fuel burn rates at the various power settings, the actual power settings, or the actual flight durations at those power settings. Minimum Control Airspeed Loss of thrust in one engine of a multi-engine airplane will reduce or eliminate climb capability, and will introduce directional control problems that result from asymmetric thrust in non-centerline thrust configuration airplanes. Minimum control speed airborne (Vmca) is defined by 14 CFR part 23 as the minimum speed at which directional control, under a very specific set of circumstances, can be maintained with the critical engine inoperative while airborne in a multi-engine airplane. Vmca does not require or provide for a positive rate of climb. Vmca is a function of multiple factors, and is established by the manufacturer during flight test. Because the airplane had accumulated less than 1 hour of total flight time in its test program, Vmca had not been yet determined. The Airplane Flying Handbook (AFH, FAA-8083-3) contained the following text regarding engine failures. "A takeoff or go-around is the most critical time to suffer an engine failure. The airplane will be slow, close to the ground, and may even have landing gear and flaps extended. Altitude and time will be minimal...Airplane climb performance will be marginal or even non-existent, and obstructions may lie ahead...With loss of an engine, it is paramount to maintain airplane control and comply with the manufacturer's recommended emergency procedures." The pilot stated that because Vmca had not yet been determined, the flight test program's engine failure plan called for the pilot to reduce thrust in the operating engine to idle, and land wherever practical. He reported that following the loss of left engine thrust, he had to maintain some thrust on the right engine in order to avoid striking the parked airliners. He also reported that the resulting thrust asymmetry resulted in his limited ability to control the airplane flight path. Engine FADEC Data The engine was equipped with limited non-volatile memory as part of the FADEC. The pilot sent both engines (including their FADEC modules) to the engine manufacturer in the Czech Republic for analysis, but the manufacturer only provided limited feedback, which did not provide any useful information regarding the reason(s) for the engine failure. Onboard Video Recording