North American AT 6 N3198G accident near Mesa, Arizona

Probable cause

The pilot's inability to return to the departure airport due to an unspecified in-flight emergency for reasons that could not be determined during a postaccident examination of the airplane.

NTSB analysis

The airline transport pilot and a passenger departed on a local flight as part of a flight of two airplanes in daytime visual meteorological conditions. Shortly after takeoff, witnesses heard the engine popping; another witness reported a possible loss of power. The airplane entered a right turn and appeared to slow. It subsequently impacted the ground and a postimpact fire ensued. Recorded communication obtained from the air traffic control tower revealed that the pilot transmitted a mayday call before the accident; however, he did not state the nature of the emergency. Postaccident examination of the airframe, flight control system, and the engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

The airplane was originally equipped with left- and right-wing fuel tanks, as well as a reserve tank located within the left tank. Maintenance records revealed that the fuel system was modified from its original configuration to remove the reserve tank and interconnect the left and right tanks, therefore allowing for an "On/Off" selection and eliminating the need to switch tanks in flight. The fuel system was again reconfigured; however; no entries in the maintenance records were found regarding this modification. Postaccident examination of the airplane and interviews with the operator revealed that the tank interconnect had been removed, and that the reserve port on the fuel selector valve had been plugged with a blanking cap. The fuel selector valve face displayed four quadrants, one each for the Left, Right, and Off positions, and a blank quadrant where the Reserve position had been previously. Although the Reserve position was not marked, the selector could still be moved to that position, which would result in a loss of fuel flow to the engine. During the wreckage examination, the fuel selector valve was found in a position consistent with the reserve position; however, the fuel selector valve position at the time of the accident could not be determined.

It is possible that, if the airplane experienced a momentary loss of power, and in accordance with the practice most commonly used by T-6 pilots, the pilot would have selected what was the "reserve" position (although not marked), even though that port was plugged. This would have led to a total loss of engine power due to fuel starvation.

Text from the NTSB. Open the NTSB docket for WPR16FA112 for the full record.