NORTH AMERICAN F51 — Maricopa, AZ

What happened

The commercial pilot and pilot-rated passenger took off during the morning for a personal flight to perform aerobatic maneuvers in the World War II fighter airplane. Witnesses reported seeing the airplane performing acrobatic maneuvers. The airplane was last observed by the witnesses descending in a nose-down spiral until it impacted the ground, where a postimpact fire ensued. All the witnesses that commented about the airplane's engine stated that they heard the engine running during the nose-down spiraling descent, and some of the witnesses stated that they heard a change indicating that the engine was going from full power to a lower power setting. Postaccident examination of the airplane revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

A performance study based on radar data indicated that the airplane climbed rapidly from 5,700 to 7,700 ft mean sea level (msl), which required a significant nose-up attitude and a climb rate of over 8,000 ft per minute. It is likely that the airplane's airspeed slowed at the top of the climb and that the airplane experienced an accelerated stall and entered a spin.

According to the airplane flight manual (AFM), power-on spins should never be intentionally performed in this airplane and recovery from a power-on spin required that the pilot close the throttle completely and apply controls for recovery. The manual stated that "after the rudder is applied for recovery, between 9,000 to 10,000 ft of altitude is lost." However, the maximum radar recorded altitude of 7,700 ft msl was about 6,426 ft above ground level; therefore, there was insufficient altitude available to recover the airplane from a spin. Further, the change in engine sound heard by some of the witnesses was consistent with the closing of the airplane's throttle during a power-on spin recovery as called for by the AFM.

Although ethanol was detected in the pilot's tissue samples, the levels detected were not consistent with levels expected from ingestion, which suggests that the ethanol may have been from postmortem production. Further, the level detected in the liver was below that generally considered impairing. Therefore, given the low levels of ethanol detected, some or all which may have resulted from postmortem production, it is unlikely the ethanol detected impaired the pilot at the time of the accident.

The pilot's medical records indicated that he had a history of atrial fibrillation that resulted in an embolic stroke about 4 years before the accident. The neurological deficits from the stoke had resolved, and his heart disease had been effectively treated with no evidence of recurrence. Therefore, there was no evidence that the pilot's medical condition contributed to the accident.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.