Accident Details
On May 14, 2020, about 0950 mountain standard time, a Cessna 172P, registration N63931, was substantially damaged when it was involved in an accident near Tucson, Arizona. The pilot, who was the sole occupant, was not injured. The flight was conducted as a Title 14 Code of Federal Regulations Part 91 aerial survey operation.
The pilot reported that during the preflight inspection, he calculated fuel burn and sumped the fuel tanks, noting no particles. The engine started and ran up with no anomalies. Both fuel gauges indicated full, and the fuel selector was set to BOTH. Takeoff and the aerial observation proceeded normally.
About 3.5 hours into the flight, the engine began to sputter. The pilot double-checked the fuel selector, enriched the mixture, checked the magnetos, and inspected the gauges. The left tank gauge read empty, while the right showed full. He immediately turned away from nearby mountains and initiated an off-field landing toward a roadway. During short final, the airplane encountered a downdraft and landed short of the roadway in heavy brush. The right wing sustained substantial damage during the landing.
Post-Accident Examination
Postaccident examination by a Federal Aviation Administration inspector revealed the fuel selector in the BOTH position. No visible signs of fuel or oil leaks were present. Fuel was found in the right fuel tank up to the fuel selector valve, and all selector positions had good detent. The fuel strainer bowl and main fuel line to the carburetor contained fuel. The propeller rotated freely with no abnormalities.
Later, the airframe was secured, an undamaged propeller installed, and an external fuel tank attached to the fuselage fuel lines. The engine started using its key and normal procedures. After warm-up, the fuel selector was moved from BOTH to LEFT and then RIGHT; the engine ran smoothly throughout.
Maintenance and Pilot Statements
The accident flight was the first flight after routine maintenance, which included an oil change, spark plug gap checks, magneto timing, and cylinder compression. The director of maintenance stated that standard policy is to place the fuel selector on the left tank after maintenance. He contacted the mechanic who worked on the airplane, who recalled moving the selector to the left when moving the airplane to the tiedown area.
The operator reported that pilots are instructed to fly with the fuel selector in BOTH at all times to avoid running a tank dry. He noted that the end of the "busy" season was May 31, 2020, and that pilots sometimes become "burned out" or "complacent" near season's end.
During a follow-up conversation, the pilot stated he had flown the same airplane for six months. He said the fuel selector was in BOTH before and during the flight, and he observed no abnormal gauge indications or engine noises prior to the sputter, which sounded like the engine was "choking." After the engine quit, he saw the left gauge empty and right full but did not switch the selector to the right tank during restart attempts. He used primer and throttle; the engine briefly received fuel but would not sustain operation. When informed of the maintenance facility's policy, he said he saw the fuel selector on the left tank before the flight and switched it to BOTH.