What happened
While climbing through 10,000 feet near Machmell, British Columbia, a Piper PA-31 Navajo experienced an engine fire on its number-two engine. The pilot had previously observed fluctuating fuel pressure on this engine, a symptom that had been addressed by maintenance through the replacement of a fuel flow transducer, but the underlying issue persisted. During a radio conversation with maintenance personnel, an explosion occurred, and the passenger observed flames emerging from the engine's lower cowl vents.
Following emergency procedures, the pilot shut down the engine, though the fire continued for several minutes. The aircraft was diverted to Port Hardy, where it landed safely without injuries. However, the aircraft sustained significant fire damage to the engine nacelle, wing skin, and landing gear door.
The investigation
Investigators examined the engine-driven fuel pump (EDFP) and found that fuel was leaking from the gasket between the pump body and the relief valve cap. Technical analysis revealed that the four screws securing the cap had insufficient torque, ranging from 0 to 3 inch-pounds, far below the required 23 to 25 inch-pounds.
This loss of torque was attributed to a phenomenon known as "gasket set," where the gasket remains compressed after the engine components expand and contract due to high operating temperatures. The investigation also looked into the aircraft's maintenance records and found no evidence that the required Service Bulletin (SB) regarding this specific pump had been performed. Furthermore, the investigation identified a cockpit ergonomics issue: the placement of headset jacks obstructed access to the high-altitude boost pump circuit breaker, forcing the pilot to disconnect his headset and temporarily degrading communication during the emergency.
Findings
- The engine fire was caused by fuel leaking from the engine-driven fuel pump into the vicinity of hot turbocharger and exhaust components.
- The fuel leak was a direct result of failing to comply with the manufacturer's Service Bulletin requiring the retorquing of the relief valve cap screws after an initial period of engine operation.
- The loss of screw torque was caused by the compression and permanent deformation (setting) of the pump gasket during thermal cycles.
- The pilot's emergency response and communication were hindered by the physical obstruction of the boost pump circuit breaker by the headset jack installation.