What happened
During a test flight following maintenance, a turboprop engine experienced a sudden loss of power. This failure prevented the aircraft from maintaining its flight altitude, forcing the pilot to perform an emergency landing. The impact of the forced landing resulted in substantial damage to the aircraft. At the time of the incident, the engine had recorded approximately nine total flight hours.
Findings
An investigation into the fuel pump revealed significant discrepancies in the condition of the internal components. While the driven gear showed almost no signs of wear, the high-pressure drive gear exhibited missing material and worn teeth. A metallurgical analysis determined that the drive gear was manufactured using a material similar to 300-series stainless steel, which lacks the hardness of the required M50 steel. The driven gear, however, was correctly composed of the specified M50 steel.
Following the discovery, the aircraft manufacturer identified that three gears made from the incorrect, softer stainless steel had been mistakenly included in the production inventory. The gear installed in the engine involved in the accident was one of these three nonconforming parts, and the location of the remaining two gears remains unknown. The investigation concluded that the use of a softer-than-specified material in the drive gear caused it to fail, leading to insufficient fuel flow and the subsequent loss of engine power. In response, the manufacturer inspected existing stock and issued service bulletins and information letters to both civilian and military operators using the affected fuel pump part number.