N63931Cessna 172P · 1981

On May 14, 2020, about 0950 mountain standard time, a Cessna 172P, N63931, was substantially damaged when it was involved in an accident near Tucson, Arizona. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 aerial survey flight.

The pilot reported that during the preflight inspection he calculated fuel burn and sumped the fuel tanks; no particles were noted. He started the engine and performed an engine run-up with no anomalies noted. Both the left and right fuel gauges showed full, and the fuel selector was on both. He took off and conducted his aerial observation flight. About 3.5 hours into the 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. During landing the airplane’s right wing sustained substantial damage.

Postaccident examination of the airplane by a Federal Aviation Administration inspector found the fuel selector in the BOTH position. There were no visible signs of fuel or oil leaks. Fuel was present in the right fuel tank to the fuel selector valve. All positions of the fuel selector had a good detent. The fuel strainer bowl was removed, and fuel was present. In addition, fuel was present in the main fuel line going into the carburetor. The propeller rotated freely with no abnormalities noted. At a later examination, the airframe was secured, an undamaged propeller was installed, and an external fuel tank was attached to the fuselage fuel lines. The engine was started using its key and normal starting procedures. After the engine warmed up, the fuel selector was moved from both to left, and then the right positions. The engine ran smoothly throughout the engine run.

The accident flight was the first flight post-maintenance. The airplane underwent routine maintenance that included an oil change, spark plug gap checks, magneto timing, and cylinder compression. The director of maintenance reported that it is standard policy to place the fuel selector on the left fuel tank after conducting maintenance. He further mentioned that he contacted the mechanic who conducted the work on the accident airplane, and he specifically recalled moving the fuel selector to the left position when the airplane was moved to the tiedown area and secured.

The operator reported that he specifically instructs pilots to fly with the fuel selector in the BOTH position at all times to avoid running one fuel tank dry. 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.

During a follow-up telephone conversation with the pilot, 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 policy 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.