Cessna 172 N63931 accident near Tucson, Arizona

Probable cause

The pilot improper fuel management, which resulted in running the left fuel tank empty and a subsequent total loss of engine power due to fuel starvation.

NTSB analysis

The pilot reported that about 3.5 hours into an aerial observation flight, the engine started to sputter. He stated that he double checked the fuel selector, enriched the mixture, checked the magnetos, and looked at the gauges. The left tank fuel gauge indicated it was empty and the right tank fuel gauge indicated it was full. He immediately turned away from nearby mountains and initiated an off-field landing toward a roadway. During short final, he encountered a downdraft, and the airplane landed short of the roadway in heavy brush, substantially damaging the right wing.

A postaccident wreckage examination and engine run did not reveal any anomalies with the airframe or engine that would have precluded normal operation. The accident flight was the first flight post-maintenance. The maintenance facility’s standard policy for mechanics is to place the fuel selector on the left fuel tank after conducting maintenance. In addition, the mechanic who conducted the work recalled moving the selector to the left when the airplane was moved to the tie-down area and secured.

The operator reported that he specifically instructs pilots to fly with the fuel selector in the BOTH position at all times. He further mentioned that the end of the “busy” season is May 31, 2020, and that it is not uncommon for pilots to get “burned out” or “complacent” toward the end of a season.

When the NTSB IIC contacted the pilot to ask additional questions about the event, he reported that he had been flying the same airplane for the last 6 months and knew it well. He said that the fuel selector was in the BOTH position before and during the flight. He said he did not note anything abnormal with the fuel gauges during the flight. Nor did the engine make any abnormal noises prior to it starting to sputter, he said it sounded as if the engine was “choking.” He further reported that after the engine quit, he noticed that the left fuel gauge indicated empty and the right indicated full, but he did not turn the selector to the right fuel tank when attempting to restart the engine. He used primer and throttle; the engine got some fuel, but it would not continue to run. When the pilot was informed of the maintenance facility’s standard procedures regarding the fuel selector placement, he stated that he saw the fuel selector was on the left tank and he switched it to BOTH before the flight.

Despite the pilot saying that the fuel selector was on the BOTH position both before and during the flight, he never mentioned that it was ever on the left tank until after learning about the maintenance facility’s standard procedures. In addition, a postaccident engine examination revealed fuel in the fuel lines throughout the airframe all the way to the carburetor inlet, and the engine ran with no issue. Therefore, it is likely that the pilot did not ensure the fuel selector was in the BOTH position after it came out of maintenance, nor was he properly monitoring the fuel gauges during the flight which resulted in a total loss of engine power due to fuel starvation.

Text from the NTSB. Open the NTSB docket for WPR20LA147 for the full record.