Piper PA-28-161 N4122T accident near Chandler, Arizona

Probable cause

Failure of the maintenance personnel to ensure adequate torque of a fuel line fitting, which resulted in an in-flight fire.

NTSB analysis

The certificated flight instructor (CFI) and private pilot were performing touch-and-go practice takeoff and landings. When the airplane was turning to the crosswind leg of the traffic pattern they began to see smoke in the cockpit, which was likely coming through the defroster vents. With the airplane about 1,600 feet mean sea level, the CFI assumed authority of the controls and declared an emergency to the tower air traffic controller. Within several seconds the smoke became thick in the cabin, and the CFI banked the airplane right with the intent of landing on the closet runway. The smoke in the cockpit became so thick that the CFI lost visual reference outside. He flared the airplane and it touched down hard. After the airplane came to a stop, the CFI and the private pilot exited. A review of the airplane maintenance logbooks revealed that the last annual inspection was completed 2 days prior to the accident. According to the records, the airplane had accrued approximately 4 additional flight hours since that inspection. An examination of the firewall revealed that its left side had a white coloration which turned to a black soot color on the right side, consistent with the fire originating on the left side of the engine. The fuel line leading from the engine driven fuel pump to the carburetor was found disconnected at the fuel pump. There was no visible impact damage to the “B” nut on the line or to the fitting on the fuel pump, indicating the line was not connected at the time of impact. Based on this evidence, it is likely that the “B” nut on the line was not properly tightened, which allowed it to back off due to normal engine vibration, resulting in the line disconnecting during the flight. Pressurized fuel from the fuel pump then sprayed onto the left side of the exhaust system and ignited. The engine manufacturer recommended that the fuel line “B” nut torque should be 35 in-lbs.

Text from the NTSB. Open the NTSB docket for WPR10FA264 for the full record.