North American SNJ-2 N52900 accident near Wilkes-Barre, Pennsylvania

Probable cause

A partial loss of engine power for undetermined reasons. Also causal was the pilot’s exceedance of the airplane’s critical angle of attack while maneuvering for a forced landing following the loss of engine power, which resulted in an aerodynamic stall and loss of control.

NTSB analysis

The accident airplane was one in a flight of six other airplanes departing on a practice flight in preparation for an airshow routine. The accident pilot’s wingman stated that they had just taken off, and that the accident pilot did not look over at him to check that his landing gear was up as he normally did. The wingman noted that the accident airplane’s landing gear was retracting, that the airplane began decelerating, and that he heard the accident pilot transmit over the radio that he had an emergency. The accident airplane turned to the left, and as its angle of bank increased past about 20°, the airplane slowed further, the bank continued to increase, and the airplane began descending. The airplane’s smoke system then came on, the airplane impacted the ground, and a post-impact fire ensued.

A video provided by a witness on the ground captured popping noises similar to back-firing of the engine before the airplane turned left and pitched down to ground contact. No black smoke was observed emanating from the airplane before the accident.

Postaccident examination of the airplane revealed that it was severely fire damaged. No evidence of any preimpact failures or malfunctions of the airframe or engine that would have precluded normal operation were identified. Examination of the propeller revealed signatures consistent with low power at the time of impact. Given this physical evidence, the pilot’s report of an inflight emergency, and the witness video that depicted abnormal engine sounds, it is likely that the engine at least partially lost power during the initial climb, which precipitated the pilot’s break out from the formation.

On the day before the accident, the accident pilot arrived at the airport late due to weather. He reported that the engine was “banging” while operating on the left magneto during a magneto check. Troubleshooting by the director of maintenance (DOM) revealed that the engine was “popping and banging” while operating on the left magneto, and during the idle-power P-lead check for proper grounding of the magnetos, when the magneto switch was passed through the left magneto position on the way to the off position, the engine seemed to be shutting down as if the magneto switch had been placed in the off position. The DOM discovered that the left magneto P-lead spring at the end of the P-lead insulator was fully compressed, allowing the internal grounding spring to contact the magneto case. Inspection of the right magneto revealed that its P-lead spring was extended normally. The DOM replaced the left magneto P-lead spring and performed an engine run-up, magneto check, and P-lead check, which revealed no anomalies. Additionally, the pilot did not report any anomalies during the engine run-up before takeoff on the accident flight.

Postaccident examination revealed that the left magneto could not be fully rotated due to impact damage. Its points looked serviceable, and the coil, when tested, was within operating limits. The condenser was damaged but tested serviceable. The right magneto would rotate easily, consistent with poor magnetism, would not perform at low rpm, and would not fire on all points until it reached 180 rpm. Review of maintenance records did not reveal any entries related to the installation of the right magneto on the engine; therefore, its service history could not be determined.

According to the engine manufacturer’s troubleshooting guidance, there were 11 ignition system-related items that could cause the engine to run rough, and listed the corrective action to be taken as “apply continuity test.” Under the section on “Engine Stops,” it listed “short in the system” as a possible cause, in addition to the master switch or magneto switch being inadvertently cut off. The manual stated, “Check all wiring for security, breaks or chafing” and “Check all systems components.”

Based on the lack of anomalies found during the postaccident engine examination, it is possible that the loss of engine power occurred due to an additional undiagnosed fault with the ignition system, which could have been compounded by the poor-performing right magneto; however, the extent of the post-impact fire damage precluded a thorough examination of the ignition system wiring and components.

While breaking out from the formation, the accident pilot entered a steep left turn, which may have been an attempt to land on the crosswind runway, but also would have significantly increased the airplane’s stall speed due to the increased load factor imposed by the turn. The pilot’s exceedance of the airplane’s critical angle of attack during this turn resulted in an aerodynamic stall and the loss of control.

Text from the NTSB. Open the NTSB docket for ERA21FA334 for the full record.