ERA21LA155 · SOCATA MS894A

After takeoff from his home airport, the pilot flew his airplane to a nearby airport to practice landings. After arrival at the nearby airport, the pilot performed a touchandgo landing but decided to return to his home airport because the wind was increasing. When the airplane was in level flight at 2,500 ft mean sea level and was about 16 nautical miles from the destination airport, the upper portion of the engine cowling departed the airplane, punctured the windscreen, and became lodged against the empennage; as a result, the pilot had difficulty controlling the airplane, which was no longer able to maintain level flight. The pilot elected to make a landing in a field, and the airplane struck a large tree and a swing on residential property. During the separation of the cowling and the subsequent forced landing, the airplane sustained substantial damage. Postaccident examination of the cowling latching mechanism revealed that all four lower catches were intact, but the left forward upper lever was worn and corroded and had broken, causing the upper engine cowling to depart the airplane.

Further examination of the broken latch also revealed that the latching mechanism, which had been attached to the handle, was missing along with the shear pin, which kept the latching mechanism attached to the handle. The hook and shaft subassembly appeared to be missing in the broken latch. Also, the pinhole where the mechanism’s right side would have been attached, displayed damage around the pinhole, consistent with the smearing of material from an adjacent component sliding along the surfaces. The smearing direction was generally outward and parallel to the sliding and impact damage on the adjacent rivet head. In addition, material was deformed outward from the pinhole, including outward smearing on the hole edge. This deformation was parallel to and consistent with the other smearing features on the latch body interior.

Witness marks and the absence of the hook and shaft subassembly were consistent with the loss of the pin. Thus, when the shear pin, which was not recovered, fractured, the pin remnant likely came out of one of the holes and then tore out of the other hole in a bending direction, damaging the adjacent housing rivet head.

The pilot had performed, as part of his pre-flight inspection before the accident flight, a check of the cowling latches in accordance with a manufacturer service bulletin and a Federal Aviation Administration airworthiness directive (AD), both of which had been issued to prevent the possible loss of an engine cowling due to improper latching of locks and cowl lock wear. The pilot reported that the preflight inspection was “normal.”

The AD required in part that, maintenance personnel visually inspect the engine lower cowling metal centering tabs and the upper cowling centering pins for wear of the metal tab receiving holes and wear of the centering pins to ensure proper mating of the upper and lower cowling. The metal centering tabs and cowling centering pins were to be replaced if found to be worn. The AD also required maintenance personnel to inspect the engine cowling locking mechanism and, if deterioration in locking push force is evident, adjust the engine cowl lock by removing the cotter pin in the upper catch, threading the latch trunnion into the upper catch a distance of one or more turns, and reinserting the cotter pin. These inspections were to occur within 25 hours after the AD was issued and then within 100 hours of time in service from the last inspection.

Review of the airplane’s maintenance records found logbook entries from 1977 to 2015 that indicated that the recurring AD had been accomplished and that no adjustments were needed, and no defects were noted. However, the AD was not consistently performed according to the specified time requirement. Additionally, between the time of the last inspection and the accident, the airplane had been operated for about 204 hours, but maintenance records showed no other entries indicating compliance with the AD. The most recent document in the logbook, an AD compliance report for the airplane, showed that the AD was previously complied with, even though it was a recurring AD. Therefore, the upper engine cowling likely separated from the airplane due to maintenance personnel’s failure to perform the required inspection of the engine cowling latches.

Verbatim NTSB analysis and probable cause from the NTSB dataset