What happened
Shortly after departing the airport, the aircraft encountered an emergency involving the number three engine. A fire broke out in this engine compartment, necessitating immediate action from the crew. The onboard fire suppression system was activated, and the fire bottles successfully extinguished the flames. Following the resolution of the immediate threat, the flight continued its journey back to the departure airport. The aircraft landed safely at the original airport without any further complications or incidents.
The investigation
A thorough examination of the aircraft was conducted to determine the root cause of the engine fire. Investigators discovered that a secondary fuel line had become detached from a B-nut ferrule fitting located at the fuel flow divider manifold. This separation allowed fuel to leak directly into the engine cowling area, creating the conditions for the fire.
Further review of the FAA Safety Data Reporting (SDR) database revealed that this was not an isolated incident. There were records of five prior occurrences where either a primary or secondary fuel line had pulled out of the same type of B-nut ferrule fitting on similar aircraft. This pattern indicated a systemic issue rather than a random failure.
Findings
The investigation highlighted a known maintenance vulnerability in the fuel system design. At the time of the incident, a factory modification to the fuel lines was being implemented fleet-wide to address this specific risk. However, this corrective action had not yet been completed on the aircraft involved in this event. The failure to complete the modification left the aircraft susceptible to the fuel line detachment that caused the emergency.
Safety message
This incident underscores the importance of timely implementation of manufacturer safety modifications. Even when a fleet-wide fix is in progress, individual aircraft remain at risk until the work is completed. Operators must ensure that all applicable service bulletins and modifications are executed promptly to prevent recurring mechanical failures.