Accident Overview
Shortly after takeoff, while climbing to cruise altitude, the pilot reported that the left engine cowl assembly had separated. Witnesses observed the airplane at low altitude, noting it was yawing, sputtering, and rocking back and forth. They indicated that the left engine was not running and that the airplane banked sharply to the right before disappearing behind trees. The aircraft subsequently crashed. The pilot, the sole occupant, was killed.
Investigation Findings
An investigation revealed that the left propeller had not been feathered. The left engine cowling was found 1.8 miles from the accident site. Examination of the cowling showed that the three primary (eyebolt) cowl fasteners on the outboard side of the left upper cowl were unlocked, and seven other cowl attaching studs (screws) were missing.
The cowling had been removed 16 days before the accident to install an oil/air separator. This was the first flight since that maintenance was performed. The mechanic who completed the work stated that he noted several cowl stud fasteners were missing and that he had notified the pilot. The pilot reportedly replied that he had some fasteners and would take care of the problem.
Sequence of Events
The aircraft departed and began a normal climb. Shortly afterward, the pilot communicated that the left engine cowl had come off. Witnesses then observed the aircraft at low altitude exhibiting erratic behavior, including yawing and sputtering. The left engine appeared to be inoperative, and the aircraft banked sharply to the right before descending out of view behind trees. The crash site was located, and the pilot was found deceased.
Probable Cause
The probable cause of the accident was an in-flight separation of the left engine cowl assembly that was not properly latched, and failure of the pilot to maintain minimum control speed, which resulted in his loss of aircraft control. Factors related to the accident were: an inadequate preflight inspection, inadequate markings/alignment indications to assure that the cowl fasteners were locked, and an insufficiently defined procedure in the flight manual for checking the cowl fasteners.