What happened
On June 8, 2015, a Fokker F28 F100, registration HB-JVG, was performing a scheduled passenger flight from Warsaw to Zurich. While cruising at flight level 340, the crew received an engine failure warning for engine number one. Following the alert, parameters for the engine and thrust levels began to decline, prompting the crew to manually shut down the engine.
The crew first attempted to restart the engine using the windmilling method at a speed of 200 knots and an N2 rotation of 18%, but this was unsuccessful. A second attempt was made using the starter motor, which also failed and resulted in the destruction of the starter unit. The flight crew elected to continue the flight to Zurich, where the aircraft landed without further incident. There were no fatalities, though 5 crew members and 96 passengers were on board, with some crew members sustaining minor injuries.
The investigation
Investigators examined the engine cowling and discovered significant amounts of metal shavings, which were identified as debris from the disintegrated starter. Traces of black engine oil were also present, indicating that the engine had been windmilling for an extended period without sufficient lubrication to the main bearings. No contaminants were found in the fuel filter.
Following the incident, ground testing was performed. While an initial ground start attempt failed, the engine operated normally after the fuel flow regulator (FFR) was replaced. The faulty regulator was sent to the manufacturer for analysis. The investigation revealed that the drive gear teeth were so heavily worn that they could no longer transmit torque, and the drive shaft had actually broken.
Findings
- The engine failure was caused by a defective fuel flow regulator.
- The specific regulator had been in service for 16,907 flight hours since its last overhaul.
- The manufacturer had recommended a mid-life inspection between 9,000 and 12,000 flight hours to detect wear, and advised that the component should not remain installed for more than 16,000 hours without refurbishment.
- The component exceeded the manufacturer's recommended operational limits for inspection and overhaul, which prevented the timely detection of the advanced wear that led to the shaft failure.