Accident Details
On August 20, 2022, about 1140 central daylight time, a Cessna 150F, registration N8797G, was substantially damaged during a forced landing near Berry, Alabama. The aircraft was operating under Title 14 Code of Federal Regulations Part 91 as an instructional flight with a flight instructor and student pilot on board; both occupants were not injured.
The student pilot reported that the engine lost partial power while the airplane was configured in cruise flight. He described the sensation as feeling like one cylinder had quit, without the vibration associated with a broken connecting rod. The instructor subsequently assumed control, adjusted to best glide airspeed, performed remedial actions to restore power, and searched for a suitable forced landing site during the descent. Preparing for a landing in trees, the instructor spotted a clearing that had been cut over by local loggers at low altitude. He maneuvered the airplane into the clearing, where it collided with terrain and cut trees, substantially damaging the engine compartment, cabin, and both wings.
The airplane came to rest upright, nose-down on the propeller and the right wing tip, in rough terrain among cut timber.
Wreckage Recovery and Disposition
The terrain and the airplane's resting position precluded an on-site examination. The wreckage was recovered to a secure facility for further investigation. However, before the engine examination could be completed and the wreckage released, the insurance carrier sold the wreckage. The buyer, unaware that the airplane was being retained as evidence, began disassembling it for part sales. Before the aircraft could be located and arrangements made for an engine examination, the buyer had partially disassembled the engine.
Engine Examination
An inspector from the Federal Aviation Administration examined the partially disassembled engine. Hand rotation at the propeller flange was smooth with no issues. Compression could not be confirmed because the upper cylinder spark plugs, cylinder covers, push rods, and rocker assemblies had been removed. It could not be determined from which cylinder the spark plugs, push rods, and rocker arms had been removed. Four spark plugs were described as oily, with carbon buildup, corroded, and contaminated.
The left magneto was too damaged and disassembled to produce a spark, and sufficient rotation could not be applied to the right magneto to achieve a spark. The carburetor was sheared off from the intake manifold. The No. 1 cylinder was cracked at the rocker box, with the crack extending the full length across the mounting pin section; the bushings were found loose due to expansion from the crack.
Photographs were examined by the manager of product field performance for the engine manufacturer. According to the manager, the exhaust valve in the No. 3 cylinder was stuck in the open position. With the rockers removed, both valves should have been pressed closed by valve spring tension. A stuck exhaust valve would result in substantial power loss. Additionally, the manager stated that bushings were not installed in the rocker boxes of cylinders at the factory; the bushings pictured in the No. 1 cylinder rocker box reflected a repair performed at some point during the cylinder's service life. The loose bushing would affect dry lifter clearance and adversely affect valve performance.
The engine maintenance records were not available for review, and the maintenance history of the engine could not be determined.