In-Flight Engine Fire on a Piper PA-31 Navajo

Incident Overview and Emergency Response On a flight from Machmell to Nanaimo, British Columbia, a Piper PA-31 Navajo (serial number 31-7752151) experienced an in-flight fire on its number-two engine. The aircraft was climbing through 10,000 feet when the pilot observed low and fluctuating fuel pressure readings. After hearing an explosion and seeing flames through the lower cowl vents, the pilot shut down the engine using the emergency checklist. The fire was extinguished after three to four minutes, and the aircraft diverted to Port Hardy, where it landed safely with emergency services standing by. No injuries were reported, but the aircraft sustained major fire damage. The PA-31 Navajo is powered by two Lycoming TI0-540-J2BD engines. The occurrence aircraft had 10,250 airframe hours, and the number-two engine had 1,145 hours since overhaul. The engine-driven fuel pump (EDFP) is located approximately 8.5 inches forward and below the turbocharger and other hot exhaust system components. ## Technical Investigation and Root Cause A technical inspection revealed extensive fire damage to the engine accessory section, engine mount, lower cowling, right main gear door, wing lower skin, flap, and engine cargo pod. The flame track extended from the cowl door to the aft end of the nacelle cargo pod, measuring about 14 inches wide. The investigation determined that the EDFP, part number RG 9080 J4A, had been leaking fuel at the gasket between the pump body and the relief valve cap. TSB Engineering Branch analysis found that the leak was caused by insufficient torque on the four relief cap attaching screws, which ranged from 0 to 3 inch-pounds compared to the specified 23 to 25 inch-pounds. The pump manufacturer, Crane-Lear Romec, had identified that the gasket could take a “set” due to thermal expansion, reducing screw torque over time. Air temperatures in the engine compartments can reach 200°F (93°C), especially after engine shutdown, which accelerates this process. ## Maintenance and Regulatory Context Lycoming issued Service Bulletin (SB) 406 on November 19, 1976, and later SB 529 on November 1, 1997, requiring torque checks and re-torquing of the screws after 5 to 10 hours of engine operation, followed by leak inspections every 50 hours or 6 months. However, the SB cannot be performed at pump or engine overhaul because it requires a minimum of 5 hours of operation. In Canada, compliance with service bulletins is not mandatory under the Canadian Aviation Regulations (CARs), though logbook records are required when performed. Investigators found no evidence that the applicable SB had been carried out on the occurrence aircraft. The fuel leak was a direct result of not performing the work set out in the SB, and the leaked fuel was likely ignited by the turbocharger or exhaust system. ## Cockpit Design and Communication Issues During the emergency, the pilot was unable to access the high-altitude boost pump circuit breaker because the headset jacks interfered with the breakers. He had to remove his headset jacks to pull the circuit breaker, which slowed his response and degraded radio communication. This headset installation issue is reported to be common in Navajo models produced after 1976 and may also affect pre-1976 models with optional high-altitude boost pump systems. ## Safety Actions and Corrective Measures The maintenance facility submitted a Service Difficulty Report to Transport Canada. Crane-Lear Romec issued SB 101SB020 in July 1997, advising re-torquing of the screws after five hours of service and leak inspections at every engine inspection. Transport Canada, in consultation with the U.S. Federal Aviation Administration, issued Airworthiness Directive AD 98-18-12, mandating compliance with Textron Lycoming SB 529A, which requires compliance with Crane-Lear Romec SB 101SB020, Rev. 2. As a longer-term solution, the pump manufacturer redesigned the fuel pump to use an O-ring instead of a gasket to prevent torque loss due to thermal expansion. As of October 1999, a service bulletin detailing the modification was under review by Textron Lycoming and the FAA. The TSB also sent an Occurrence Bulletin regarding the headset jack location to the involved maintenance facility and the U.S. National Transportation Safety Board.