Palm Springs, CA, USA
N737NB
CESSNA 172
The student pilot and her flight instructor performed three takeoffs and landings to a full stop prior to the accident. During this time, the flight instructor observed no engine anomalies. He exited the airplane and the student pilot then performed two successful takeoffs and landings to a full stop. On the third landing attempt, the airplane touched down hard, bounced, and began to porpoise. The student pilot attempted a go-around and started a shallow climb. The airplane leveled off about midfield before it turned left and entered a nose-down dive and impacted the ground. Surveillance video showed the airplane in a shallow climb and subsequently captured it leveling off before starting the left turn. A postaccident engine examination revealed severely worn intake tappets and camshaft lobes; however, this wear would have occurred over time and is not likely to have demonstrated as a sudden loss of power. Further, it is doubtful that the engine suffered a loss of power as the student pilot and flight instructor did not recall noticing any deficiencies with the engine prior to this flight and no other abnormalities were noted during the engine examination. One witness reported that the airplane appeared to be producing less power than it did during prior operations in the traffic pattern. However, the investigation could not substantiate this statement with other evidence. The investigation did not find any preimpact mechanical anomalies or failures with the airplane’s flight control system. The investigation was unable to determine why the student pilot made a left turn after initiating the attempted go-around as the student pilot was unable to recall any details about the accident flight. The available evidence is consistent with her failure to maintain aircraft control during the subsequent climb and exceeding the airplane’s critical angle of attack, which resulted in an aerodynamic stall and subsequent impact with the ground.
On December 4, 2020, about 1411 Pacific standard time, a Cessna C172N, N737NB, was substantially damaged when it was involved in an accident at Palm Springs International Airport (PSP), Palm Springs, California. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. According to her flight instructor, they departed from a nearby airport in Palm Springs, California, and flew to PSP to perform takeoffs and landings. They completed three takeoffs and landings with the student pilot as the sole manipulator of the. At the conclusion of the third landing the instructor exited the airplane, so the student pilot could fly solo. The student pilot’s first two takeoffs and landings to a full stop were uneventful. However, during her third attempt, the instructor observed the airplane touch down hard on the nose landing gear, bounce, and the airplane began to porpoise. The airplane then entered a climb when it was about halfway down the runway., A few seconds later the airplane slowed and began a left turn as it entered a nose down dive and impacted the ground. According to the instructor, the wing flaps were deployed when the airplane descended into the ground. The instructor reported that he did not observe any flight control or engine anomalies with the accident airplane during the practice takeoffs and landings that took place on the day of the accident, nor did he observe any anomalies with the engine power during the accident flight. The instructor further reported that he had instructed the student pilot to climb while maintaining the runway heading and to join the crosswind leg of the airport traffic pattern beyond the departure end of the runway. They had practiced go-arounds together at PSP just prior to the accident. The student pilot reported that she does not recall any performance issues with the airplane, nor does she remember the actual accident sequence. 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 of the accident flight was captured by several airport surveillance cameras, and the images were mostly consistent with the instructor and witness’ recount. The video also showed the airplane maintain a level attitude as it approached the runway and touched down near the runway numbers. The airplane bounced and porpoised before it lifted off and began a shallow climb about 1,000 ft down the runway. Once the airplane approached midfield, it leveled off and began a left turn that became progressively steeper until the airplane entered a nose down dive and impacted the ground. The wing flap position and propeller rotation could not be determined by the video. Aircraft Examination Flight control continuity was traced from the cockpit to the elevator, rudder, and ailerons. The right aileron cable displayed fracture signatures consistent with tensile overload. The wing flap actuator was not extended, consistent with a flap retracted position. Continuity of the mixture and throttle controls were confirmed from the cockpit to their respective arms on the carburetor. The fuel selector handle and valve were in the BOTH position and the left fuel tank exhibited signs of hydraulic deformation. The top spark plugs were removed, and thumb compression and suction were obtained for all four cylinders and in the proper firing order as the crankshaft was rotated by hand using a drive tool. Mechanical continuity was established throughout the engine when it was manually rotated. According to the engine manufacturer, each of the exhaust valves exhibited normal “lift action” while each of the intake valves exhibited diminished movement that was less than normal “lift.” The intake camshaft lobe for cylinders 2 and 4 was severely worn as their characteristic elliptical shape had significantly diminished and the two corresponding intake valve tappets displayed extensive spalling, pitting, and chipped edges. The combustion chambers remained mechanically undamaged, and there was no evidence of foreign object ingestion or detonation. The dual magneto remained attached to the engine accessory case and was slightly displaced from its mounting pad from impact. The spark plug leads displayed signatures consistent with normal wear and exhibited spark when the drive was rotated by hand. Large metal flakes were observed on the oil sump screen. Postaccident examination of the aircraft and engine revealed no evidence or any preimpact mechanical malfunctions or failures that would have precluded normal operation. The engine logbook did not contain any evidence that an inspection of the camshaft lobes or tappets had taken place from the date of the last major engine overhaul, which occurred in 2006. According to the engine logbook entry, the “cam” and lifters were reground during the last overhaul. A publication provided by the engine manufacturer stated that regrinding can compromise the case hardening layers of a lobe or tappet, which can result in premature wear. The publication goes on to state that the engine manufacturer “does not recommend the use of reground tappets under any circumstances.”
The student pilot’s failure to maintain aircraft control during an attempted go-around, which resulted in an exceedance of the airplane’s critical angle of attack, aerodynamic stall, and subsequent impact with terrain.
Source: NTSB Aviation Accident Database
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