What happened
While conducting a maintenance test flight in the traffic pattern, the pilot experienced a total loss of engine power. During the base leg of the flight, the engine emitted three loud bangs, after which internal components were ejected through the engine cowling. The separation of the cowling caused it to strike the empennage. The pilot was forced to perform a ditching in the ocean, where the aircraft sank and was not recovered. The pilot was not injured.
Two days prior to the accident, a company pilot had performed an unscheduled landing due to engine vibrations and rough running. On the day of the accident, the company dispatcher instructed the pilot to proceed with the test flight to ensure the airplane returned to service that same day. Prior to takeoff, the pilot completed the ground checklist, including checks of the propeller and magnetos, noting no discrepancies.
The investigation
A review of maintenance records and inspection discrepancy logs was conducted. Records showed that maintenance personnel had performed a compression check, flushed the servo unit screen, and removed and cleaned the fuel injector nozzles.
Four engine ground runs were documented; the first three runs exhibited a rough running engine and vibrations, while the fourth run showed no anomalies. Two operator inspection discrepancy records were identified. While largely identical, the first document noted that the No. 5 cylinder fuel injector nozzle required replacement but stated that no replacements were in stock. The second document indicated that the fuel injector nozzles had been cleaned and reinstalled, noting a normal ground run-up.