Accident Details
On December 4, 2020, at about 1411 Pacific standard time, a Cessna C172N, registration N737NB, was substantially damaged in an accident at Palm Springs International Airport (PSP), Palm Springs, California. The pilot, who was flying solo on an instructional flight under 14 CFR Part 91, was seriously injured.
According to the flight instructor, the student pilot had completed three takeoffs and landings at PSP with him on board, with the student as sole manipulator of the controls. After the third landing, the instructor exited the airplane so the student could fly solo. The student's first two solo takeoffs and landings to a full stop were uneventful. During her third attempt, the instructor observed the airplane touch down hard on the nose landing gear, bounce, and begin to porpoise. The airplane then entered a climb when it was about halfway down the runway. A few seconds later, it slowed and began a left turn as it entered a nose-down dive and impacted the ground. The instructor reported that the wing flaps were deployed when the airplane descended.
The instructor noted no flight control or engine anomalies during the earlier practice takeoffs and landings, nor during the accident flight. He had instructed the student to climb while maintaining runway heading and join the crosswind leg beyond the departure end. The student reported no recollection of any performance issues or the accident sequence.
Witness and Video Evidence
A witness located 150 yards east of the final impact area, who had observed the airplane during its previous pattern work, reported that the engine sounded like it was producing less power just prior to the accident.
Video from airport surveillance cameras captured the accident flight. The images were mostly consistent with the instructor's and witness's accounts. The video showed the airplane maintain a level attitude as it approached the runway and touched down near the runway numbers. It bounced and porpoised before lifting off and beginning a shallow climb about 1,000 ft down the runway. Near midfield, it leveled off and began a left turn that became progressively steeper until it entered a nose-down dive and impacted the ground. The wing flap position and propeller rotation could not be determined from the video.
Aircraft Examination
Postaccident examination traced flight control continuity from the cockpit to the elevator, rudder, and ailerons. The right aileron cable showed tensile overload fracture signatures. The wing flap actuator was not extended, consistent with a retracted position. Fuel mixture and throttle controls were continuous, and the fuel selector was in the BOTH position. The left fuel tank showed hydraulic deformation.
Engine examination: top spark plugs removed, thumb compression and suction obtained for all four cylinders in proper firing order. Mechanical continuity confirmed when the engine was manually rotated. According to the engine manufacturer, exhaust valves exhibited normal lift action, but intake valves showed diminished movement. The intake camshaft lobes for cylinders 2 and 4 were severely worn, with their elliptical shape significantly diminished, and the corresponding intake valve tappets displayed extensive spalling, pitting, and chipped edges. Combustion chambers were undamaged with no evidence of foreign object ingestion or detonation. The dual magneto was attached but slightly displaced from impact. Spark plug leads showed normal wear and produced spark when rotated. Large metal flakes were observed on the oil sump screen.
Postaccident examination revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.
The engine logbook contained no evidence of an inspection of the camshaft lobes or tappets since the last major engine overhaul in 2006. According to the engine manufacturer's publication, regrinding during the overhaul can compromise case hardening layers, potentially leading to premature wear. The publication states that the manufacturer "does not recommend the use of reground tappets under any circumstances."