Accident
On August 3, 2009, at approximately 1000 central daylight time, a single-engine Grumman American AA-1B airplane (registration N1644R) was substantially damaged during a forced landing following a loss of engine power after takeoff from Lake Whitney State Park Airport (F50) in Whitney, Texas. The airline transport pilot, the sole occupant, sustained minor injuries. The airplane was registered to and operated by the pilot. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91. The flight was originating at the time of the accident and was destined for Clifton Municipal Airport (7F7) near Clifton, Texas.
Pilot Account
According to the pilot, after an hour-long flight involving touch-and-go maneuvers, he landed at 7F7, added 10.9 gallons of fuel, and departed. After sightseeing, he landed at F50, back-taxied, and performed a magneto check before departing. Shortly after takeoff, the engine began to run rough, as if it had a fouled plug. While turning to downwind, the engine began to shake violently, and both RPM and altitude decreased. The pilot selected a field and executed a soft-field landing. During the landing rollout, the airplane nosed over and came to rest inverted. The pilot exited unassisted; moments later, the airplane was engulfed in flames.
Engine Examination
The engine, with 67 hours since major overhaul, was separated from the airframe and placed on a bench. Investigators removed the upper spark plugs and valve covers. The engine was manually rotated via the vacuum pump drive. Valve train continuity was established to each cylinder and to the oil pump. Thumb compression was developed in each cylinder. Cylinders were examined with a borescope; all cylinder domes and piston heads exhibited normal deposits. Each intake and exhaust valve was found in its respective position.
Magneto and Spark Plug Inspection
Both magnetos were removed and examined. The left magneto, tested on a bench, produced spark to all four leads. The right magneto initially produced spark to all four leads but then stopped. Internal examination of the right magneto revealed thermal damage from the post-impact fire. Spark plugs exhibited normal wear when compared to the Champion Check-A-Plug comparison card, except for the number 3 lower spark plug, which had impact damage. Additionally, the number 2 and 4 lower spark plugs were oil-soaked.
Carburetor Examination
The carburetor had impact damage to the mounting flange. The carburetor fuel inlet screen was removed and found to be clean and unobstructed. The unit was disassembled and examined; no post-accident anomalies were noted.