WPR14FA239

The pilot's loss of airplane control while intentionally maneuvering close to the ground, which resulted in the airplane exceeding its critical angle of attack in a steep bank and entering an accelerated stall.

The pilot was providing airplane rides to family and friends who had assembled at a dry lakebed. He completed two uneventful flights and then departed for a third flight from the lakebed. According to witnesses, the pilot had planned to perform a low pass over the group, and he did so just after takeoff, passing within about 50 ft directly overhead. The entire accident sequence was captured on video. The airplane dipped its right wing as it passed over the camera position and, after the pass, continued in a climbing right turn, which progressed rapidly to almost 90 degrees of bank. The excessive bank angle resulted in the airplane exceeding its critical angle of attack and experiencing an accelerated stall at an altitude too low for recovery. The airplane then entered the initial stages of a spin before striking the ground in an almost vertical attitude. Postaccident examination of the airframe and engine did not reveal any evidence of preimpact mechanical malfunction or failure. Although the reason for the aggressive turn could not be determined, the pilot's overflight of the group while maneuvering at low altitude is consistent with an intentionally-performed ostentatious display.

El Mirage Lake is located at the base of the Shadow Mountains, midway between Lancaster and Victorville, and about 1 mile north of El Mirage Field Adelanto Airport. The area is managed by the Bureau of Land Management, and aviation activities are permitted. The dry lakebed was about 5 miles long, oriented northwest-southeast, and about 2 miles wide at the accident location. Most of the lakebed was at an elevation of 2,840 ft, and the surface was dry at the time of the accident, and composed of smooth, hard-packed soil. Flight Controls All control cables for the elevator, aileron, and rudder were continuous from the control surface fittings and torque tubes through to their respective cockpit control attach points. The foot pedals and control yoke assembly sustained fragmentation and bending damage consistent with impact overload. The rudder was still attached to the vertical stabilizer at all of its hinges, and swung freely when moved by hand. The elevator swung freely when moved by hand, and the trim actuator was in place and moved appropriately in conjunction with movement of the elevator. The elevator trim actuator tube was continuous to forward cabin, where the trim wheel had separated from the cabin frame. Both ailerons sustained crush damage, and remained partially attached via their hinges at their respective locations on the wing trailing edge. The flap actuator remained attached to the center spar and torque tube. The actuator was fully retracted, which was consistent with fully retracted flaps. Control Cable Airworthiness Directive Airworthiness Directive (AD) 72-06-02 applicable to the AA-1A was issued in August 1974. The directive required inspection of the rudder, aileron, and elevator control cable group, along with their associated pulleys, in the area under the wing center spar. The cables and pulleys were inspected during the investigation in accordance with the AD and no defects were noted; additionally, a maintenance logbook entry from the last annual inspection indicated that AD had been complied with. The stall warning indicator sustained impact damage, which prevented any assessment of its working condition at the time of the accident. Engine The engine's lower cowling area was crushed, impinging the inlet air box, crushing the right-side inlet and exhaust manifold pipes along with the muffler, and separating the carburetor bowl. The engine driven fuel pump remained attached to the crankcase, contained fuel, and was free of internal obstruction. Disassembly revealed that its internal diaphragms and seals were intact, pliable, and free of damage. All fuel fittings were tight at their respective fittings throughout the engine compartment. The engine appeared to have sustained damage limited to the ancillary components, and external examination revealed no evidence of preimpact catastrophic mechanical malfunction or fire. The two-blade propeller had separated from the crankshaft flange and remained partially attached to the flywheel. The nose cone was crushed, and one blade had bent about 90 degrees midspan, opposite the direction of rotation. The blade exhibited leading and trailing edge nicks; the second blade was bent slightly forward but was largely undamaged. The left and right magnetos remained securely attached at their respective mounting pads. The ignition harnesses sustained crush damage, and were secure at each magneto and spark plug. The magnetos were removed for examination; each produced a spark at the end of their respective distributor block during hand rotation. The top spark plugs were removed and examined. The electrodes remained mechanically undamaged, coated in light grey deposits, and displayed normal, short service time wear signatures when compared with the Champion Spark Plugs AV-27 Check-A-Plug chart. The crankshaft was rotated by hand utilizing the vacuum pump output drive. The crankshaft rotated smoothly, and "thumb" compression was observed on all cylinders. Mechanical continuity was established throughout the rotating group, valve train and accessory section, and all rocker arms displayed equal amounts of lift, and were coated in clear oil. The cylinder combustion chambers were examined utilizing a borescope. The combustion chambers appeared mechanically undamaged, and there was no evidence of foreign object ingestion or detonation. The valves were intact and undamaged, and there was no evidence of valve to piston face contact. The gas path and combustion signatures observed at the spark combustion chambers and exhaust system components displayed light grey deposits and coloration. The oil filter was removed and cut open. The element appeared wet with clean oil, and free of debris. The oil screen was similarly free of debris. No evidence of preimpact mechanical malfunction or failure of the engine or airframe was noted during the examination. A complete report is contained in the public docket. Video The takeoff and accident sequence were captured on video by a member of the group, located about 1/2 mile north of the accident site. The video revealed that the airplane departed to the south, and began a climbing right turn to the north, leveling off parallel with the group at an altitude of about 300 ft agl. At that time a witness was recorded stating that the pilot should be performing a low pass. The airplane then transitioned to the east, while descending as it approached the camera. The descent progressed, accompanied by an increase in engine tone as the airplane started banking about 25 degrees to the right as it passed about 50 ft overhead, 80 seconds after takeoff. The turn continued with the airplane now banking 30 degrees until it leveled off on a southerly track a few seconds later. Seven seconds later the airplane began a climbing right turn to about 200 ft agl, reaching a bank angle of about 80 degrees as it passed out of the cameras view. One second later, the airplane reemerged, now in a 90-degree right bank, with the entire upper side of the fuselage visible. The nose then yawed about 20 degrees down while the airplane maintained the almost vertical right bank attitude. The airplane then began to rapidly descend, the nose dropped further, and the airplane rolled right and pitched down striking the ground in an almost vertical attitude about 18 seconds after the low pass. The engine could be heard operating throughout the recording, and no smoke or vapor trails were visible. Weight and Balance The engine STC SA4387NM provided for an increase in gross weight to 1,579 pounds. The airplane's basic empty weight was 1,130 pounds, and the combined weight of the pilot and passenger was about 240 pounds. The baggage compartment was loaded with about 8 pounds of equipment and tools, and according to the airplane's co-owner, prior to the first flight at the lake, the airplane's right fuel tank was full (capacity 11 usable gallons) and the left tank contained between 3 and 6 gallons. Based on these values, the airplane would have been about 100 pounds below maximum gross weight, and the center of gravity would have been about 77 inches aft of the datum. The loading graph for the airplane indicated a center of gravity range of between 75 and 80 inches when flown under the normal category. Performance An accurate assessment of the airplane's airspeed throughout the flight could not be determined. According to the AA-1A Owner's Manual, the airplane's cruise speed at 65 percent power, and 8,000 ft was 119 mph. Stall speeds in the flaps up, maximum gross weight, and forward center of gravity configuration were 63 mph at 0 degrees angle of bank, and 89 mph at 60 degrees. Maximum approved positive flight load factors in the normal category with flaps up were 3.8 G's. The FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A) described the load factors experienced by airplanes in steep coordinated turns, along with the associa