WPR12FA059

An electrical or engine electronic problem, which resulted in a loss of engine power, followed by a low-altitude stall.

The pilot, who was also the owner and builder, was flying his experimental amateur-built airplane powered by a converted automobile engine back to his home airport after a brief personal out-and-back flight. Light winds and daylight visual meteorological conditions prevailed. Radar and GPS data showed that the return portion of the flight followed an essentially straight track in the direction of the pilot's home airport at an altitude of about 1,500 feet above ground level with a groundspeed of about 100 knots. When the airplane was about 12 miles from the airport, the groundspeed decreased to about 60 knots over a period of about 25 seconds. The airplane then entered a descent of about 800 feet per minute, which it maintained for the next minute. Shortly after the start of that descent, the transponder was switched to the emergency code of 7700. About 25 seconds later, the pilot transmitted a "mayday" call to the approach controller. He stated that he had a problem, and several seconds later, transmitted that he was "going down." In the radio call, the pilot named the component that he thought was causing the problem, but the transmission quality prevented a positive determination of exactly what the pilot said. The descent rate then increased rapidly, and the airplane impacted terrain several seconds later. The damage to the rudder stop, rudder, elevator trim tab link, and elevator trim tab was inconclusive as to whether it occurred in flight or on impact. Propeller damage indicated that the propeller was not rotating or was rotating with little engine power. However, no preimpact mechanical problems with the engine, propeller gearbox, or propeller were identified. The reconstructed flight path was consistent with a significant deceleration at a near-constant altitude, followed by a descent to maintain flying speed, followed by a loss of control and/or aerodynamic stall at low altitude, from which the airplane did not recover. The airplane had slowed and started to descend when the pilot took the deliberate actions of squawking 7700 and transmitting a radio distress call. He attempted to describe the problem that he perceived. During that time, the data suggests that the airplane was still controllable and was under control. Shortly thereafter, as evidenced by the significantly increased descent rate and the pilot's transmission that he was going down, control was lost, and the airplane impacted the ground. The limited propeller damage, coupled with the engine's dependence on electricity and its electronics for continued operation, suggest that the deceleration could have been a result of an engine power loss for electrical or electronic reasons that could not be determined during postaccident examination. The specific reason for the stall could not be determined; however, the pilot may have been distracted by the emergency or the radio calls. The investigation was unable to determine the accuracy of the airspeed indicator or stall speed values. Further, the airplane does have a limited natural stall warning and no stall warning system to alert the pilot to an impending stall, particularly if he was distracted.

The flight departed from GEU, which was equipped with an air traffic control tower (ATCT) that was operating at the time of departure, and for the duration of the flight. However, after takeoff, the airplane departed the local area, and therefore, the pilot was not required to communicate again with the ATCT until he returned to the area. Since the accident occurred prior to the pilot re-contacting the GEU ATCT, no copies of GEU ATCT communications with the airplane were requested or obtained by the investigation. The bulk of the flight was conducted in the airspace designated as the "Luke Air Force Base Special Air Traffic Rule (SATR) North Area." The SATR was defined by 14CFR 93.176, and 93.177 designated the operating rules. The SATR was depicted on the applicable aeronautical navigation charts. The SATR was not active at the time of the flight, and therefore, the pilot was not required to be, and was not initially, in communication with LUF Approach. According to ground tracking radar data obtained from LUF, the pilot squawked 1200 on his transponder for almost the entire flight. At 1256:25, the data indicates that the pilot switched his transponder to 7700, the emergency code. At 1256:53, the pilot made his first call to LUF Approach with the transmission "Luke approach, Luke approach, mayday, mayday 724WD right by the substation, I have a (uncertain word) that's out of control." That transmission lasted 15 seconds. The uncertain word sounded variously like "flap" or "craft" or "prop." At 1957:00, the LUF approach controller assigned the airplane a discrete transponder code and requested the pilot's intentions. At 1957:05, the pilot transmitted five phrases regarding the fact that he was "going down," and no further transmissions were received from the airplane. The recorded communications from the airplane were generally clear, and were free from background noise. The NTSB investigator-in-charge was unable to obtain or listen to the radio communications recordings, or obtain the radar data, until 4 days after the accident, which was after the on-scene examinations had been completed. Airplane Flight Profile Data from the LUF ground tracking radar and the onboard GPS unit was used to reconstruct the profile for the entire flight. The overall ground track was meandering, consistent with the airplane being hand flown, instead of being guided by the autopilot. After the turnaround at the northwest-most extent of the flight, the airplane proceeded in an essentially straight track to the southeast, back towards GEU. Between about 1255:50 and 1256:15, the groundspeed decreased from about 100 knots to about 60 knots. Between about1256:15 and 1257:15, the airplane began a steady descent from about 2,800 feet down to about 2,000 feet msl. About 1256:25, the transponder code switched to 7700, when the groundspeed was about 62 knots, and the airplane was at an altitude of about 2,700 feet. The 1256:53 "mayday" transmission began when the groundspeed was about 50 knots, at an altitude of about 2,300 feet msl. The ground speed continued to decrease for the remainder of the flight. The ground track began a turn to the south about 1256:55. About 1257:15, the descent rate increased to over 2,000 fpm, and the data ended a few seconds later. Local terrain elevation was approximately 1,300 feet msl. Airspeed and Stall Information Since the airplane was experimental amateur-built, flight testing of the completed airplane was required to determine airspeed system calibration (and therefore accuracy) and actual stall speed values. The Vans Construction Manual enumerated the requirements and methods for the airspeed system and stall speed testing. Comparisons of the airplane's airspeed indicator (ASI) arcs and the Vans published values revealed that while most of the arcs were per the Vans values, the ASI stall speed values were not. The ASI full-flaps stall speed was 48 knots, instead of Vans value of 50 knots. The ASI no-flaps stall speed was 50 knots, instead of Vans value of 56 knots. No records of the airspeed system calibration, or stall speed testing or results were located for the investigation, and therefore the accuracy of the airplane airspeed indication system, the ASI stall speed markings, and actual stall speed values could not be determined by the investigation. According to the Vans Construction Manual "The ideal is that when a stall is encountered, the nose tends to lower, or can easily be lowered by an easing of stick back pressure or by a forward stick pressure. In most RVs, there is little advance stall warning in the form of pre-stall buffet. The buffet which does occur does so within just a mph or two of the fully developed stall." The airplane was not equipped with an angle of attack or stall warning system. Engine Electrical Information Eggenfellner Aircraft ceased production and support of the Subaru conversions about 2010. The first page of Chapter 6 (Electrical System Installation) of the Eggenfellner Installation Manual (IM) contained the following text in red typeface: "READ AND UNDERSTAND [Boldfaced type in original] - Your engine requires a constant and stable source of electricity to drive its fuel injection, fuel pumps, and the engine control computer....[T]he Subaru cannot tolerate a loss of electrical power. For this reason, we have designed fully redundant electrical and fuel systems with provisions for automatic fault management. It is imperative that you adhere to this design for your own safety and to assure ongoing maintainability. Eggenfellner Aircraft Inc. cannot be responsible for endorsing or supporting builders who deviate from our design, nor be responsible for any direct or indirect damages which may result from such deviations." The IM also stated that the "... engine uses a small, rugged, computer to control ignition, timing, and a wide variety of sensors. This computer is known as the Engine Control Module or ECM. It is also commonly referred to as the Engine Control Unit or ECU" and "The ECM must be mounted inside your cabin, away from sources of heat and vibration." The wiring block- and detail- diagrams for the engine installation depicted three master switches which controlled power to three buses: Engine, Main, and Avionics. The accident airplane was equipped with three explicitly-labeled master switches, "Master," "Avionics Master," and "Bus Master". The first two were two-position rocker switches located with nine other similar switches in a multi-switch panel typical of general aviation airplanes. The "Bus Master" was a 3-position (ON, OFF, OVERRIDE) toggle switch located a few inches above the other switch array. Although no wiring diagrams for the airplane were located, comparison of the airplane switch configuration with Eggenfellner and other documentation indicated that the "Bus Master" switch likely controlled electrical power to the engine as follows: The "ON" position powered the Engine Bus via the Main master switch, the OFF position isolated the Engine Bus from electrical power, and the OVERRIDE position powered the Engine Bus independent of the Main master switch setting. The day after the accident, the Main and Avionics master switches were found to be in their off positions, but the Bus Master was found to be in the OVERRIDE position. The investigation was unable to determine whether any first responders reset any of those switch positions. The pilot's normal and emergency procedures or procedure checklists for the airplane were not recovered. The GEU 1247 automated weather observation included wind from 080 degrees at 5 knots, visibility 20 miles, broken cloud layer at 20,000 feet, temperature 19 degrees C, dew point -7 degrees C, and an altimeter setting of 30.10 inches of mercury. The airplane came to rest upright on level hard desert terrain with a moderate cover of bushy vegetation. The wreckage was very tightly contained, and only a f