ERA25LA007 · North American NAVION

About 36 minutes after departure and while on final approach to land, the pilot heard a loud “pop” and felt heat emanating from an area behind the pilot and copilot’s seats. As the airplane approached the runway threshold, smoke accumulated in the cabin and visible flame developed. During the landing, the airplane’s nose landing gear collapsed, and the airplane came to rest on the runway. The in-flight and postaccident fire consumed a majority of the airplane. Postaccident examination revealed that the fuel selector was positioned to the auxiliary fuel tank. The right main fuel tank’s vent line was found attached, but its two hose clamps were not secured. A loose Bnut was also observed on a highpressure hydraulic hose located at the controllable relief valve in the engine compartment. The majority of the fuel supply, vapor return, and vent lines were destroyed by fire. According to the airplane flight and service manuals, when the main tanks were full, use of the auxiliary fuel tank could result in vapor return fuel being expelled overboard through the main tank vent system until at least 1 hour of flight had been completed or 10 gallons of fuel had been consumed. A preaccident photograph showed the vent outlet located approximately 10 inches aft of, and generally aligned with, the left exhaust extension. The pilot reported departing with the fuel selector positioned to the auxiliary fuel tank and making no subsequent changes. Although overboard fuel expulsion from the main fuel tank vent line was the most likely source of fuel for the fire, hydraulic fluid from the loose B-nut could not be ruled out. Thermal exposure and wreckage movement likely contributed to the loose hydraulic fitting, making it a less likely fuel source; however, due to thermal damage the source of the fire could not be determined with confidence.

Verbatim NTSB analysis and probable cause from the NTSB dataset