ERA18FA141 · Aeronca 7AC

The pilot and flight instructor were conducting a flight review in an airplane owned by a flying club. Shortly after takeoff, when the airplane was about ½ mile from the departure end of the runway, a witness reported that the airplane "suddenly went nose down." The airplane impacted a row of trees on the edge of a field in a near-vertical nose-down attitude. No ground scars were found, and no tree damage was found other than that directly above the wreckage, consistent with little or no forward speed. Thus, the airplane had likely exceeded its critical angle of attack, resulting in an aerodynamic stall from which the pilot was unable to recover.

Witness marks on the engine's crankcase nose seal area, were consistent with a directly aft impact by the propeller mounting bolt nuts and showed no indications of scraping or rotation. In addition, there was no chordwise scratching and relatively little leading edge damage to the propeller blades. The lack of any chordwise scratching and relatively little leading edge damage to the propeller blades, while not conclusive, is suggestive of slow or no rotation of the propeller as descended through the trees. Examination of the airframe and engine otherwise revealed no evidence of preimpact failures that would have precluded normal operation.

The rear seat shoulder harness anchor separated from its attachment point to the fuselage tubing during the accident sequence. Although the bolt securing the anchor was not installed in accordance with the manufacturer's instructions (the bolt head was facing up instead of the nut), the installation error likely did not cause the failure. Instead, the failure was due to the anchor sliding forward between the fuselage tubes. The investigation could not determine if the rear seat shoulder harness anchor failed due to a design issue or loads beyond the design criteria.

Verbatim NTSB analysis and probable cause from the NTSB dataset