LAX03FA005 · Grumman AA-5A

Following a loss of engine power after takeoff, the airplane banked left, hit power lines, and went nose down vertically into a mobile home. The pilot departed downwind, and a few minutes later the pilot reported to the air traffic control tower that he was returning with a problem. The pilot made a second transmission, and said that he had no oil pressure. Then he transmitted that he was landing just west of a freeway near the airport. Witnesses along the flight path heard the engine backfire, and saw the propeller stopped at the 3-o'clock and 9-o'clock positions. An intense post crash fire consumed the airframe and severely damaged the engine, with most accessories and fluid lines destroyed. The top and bottom spark plug electrodes were circular, not mechanically damaged, and the gaps were similar. The magnetos could not be tested, and the magneto to engine timing could not be established. The steel quick oil drain was closed and the o-ring was in place. All oil lines, including the pressure line to the gauge, were accounted for and all oil line B-nuts on the accessory housing were secure. Fire consumed the oil cooler. The oil pump had metal material burnished and extruded at the drive gear thrust surface; however, there was no scoring on the internal housing, the gears were undamaged, and the pump drive meshed with the crankshaft interface. The main oil pressure screen was clean. None of the combustion chambers, valves, or pistons exhibited mechanical damage. The camshaft was intact, and each of the camshaft lobes appeared similar in shape. The crankshaft remained intact. The main bearings' tangs were undamaged, and the bearings were on their respective dowels. There was no discoloration, fretting, or mechanical damage to the bearing surface. All four connecting rods remained secure at each of their respective crankshaft journals and rotated freely on the crankshaft, but all had fore and aft movement as well as lateral play. All four journals exhibited discoloration. All connecting rod bearings exhibited some extrusion and metal transfer from the bearing to the journal. Cylinder No. 1 connecting rod bearing extruded the most; it had the most metal transfer. Cylinder No. 3 bearing sustained the next worse damage. Cylinders No. 1 and 4 were the least damaged. Investigators found no obvious obstructions or preimpact contaminates in the oil passages of the engine. Despite exhaustive examinations, the exact nature of the lubricating system problem and its underlying cause could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset