Accident Summary
A pilot reported a loss of engine power during a postmaintenance test flight. The aircraft was unable to maintain altitude, forcing the pilot to conduct a forced landing. The airplane sustained substantial damage in the landing.
Investigation Findings
A teardown of the fuel pump revealed that the high-pressure drive gear teeth exhibited wear and missing material, while the driven gear showed little to no visible wear. Metallurgical examination determined that the damaged drive gear was made of a material similar to 300-series stainless steel, instead of the specified M50 steel, which is harder. The driven gear was made of a material similar to the specified M50 steel.
Further investigation by the airplane manufacturer revealed that the gear manufacturer allowed three set-up gears made from 300-series stainless steel to enter the production inventory during manufacturing. One of these gears was installed in the fuel pump on the accident airplane. The location of the two other nonconforming gears could not be determined.
Based on the evidence, it is likely that the nonconforming gear failed because it was manufactured from a softer material than specified, resulting in a loss of fuel flow to the engine and subsequent loss of engine power.
Manufacturer Response
After the findings, the manufacturer inspected its stock of gears and issued notices to customers that had engines with fuel pumps installed with the same part number gear set as the one on the accident airplane. The manufacturer also issued a service information letter and service bulletins regarding the fuel pump gear set for engines used in civilian and military applications. As of the date of the report, the two remaining nonconforming gears had not been located.