Mooney M20E N1953Y

Before the flight, the pilot requested that 20 gallons of fuel be added to each wing. A total of 40 gallons of fuel was then added to the airplane. He conducted a preflight inspection and reported sumping “both main tanks after fueling” and, once inside the airplane, he “sumped both [fuel] lines from [the] interior valve.” When the pilot started the engine, he did so with the fuel selector on the right fuel tank. All indications were normal, and, after taxiing and completing his preflight checklist, he turned on his electric boost pump, took off, and flew to a different airport where he conducted a touch-and-go landing. After the touch-and-go, he then flew back to the departure airport. During the descent for landing, he configured the airplane for landing and made sure that the electric boost pump was on and that the fuel selector handle was set. The pilot then realized that he had been flying on the right fuel tank for about an hour and had not switched fuel tanks, so he switched to the left fuel tank to balance the fuel load, as he was close to the final approach for the runway. Upon touchdown, the pilot decided to perform a touch-and-go. When the airplane was about 150 feet above ground level, the propeller rpm started to slow drastically. The pilot then banked the airplane to the left to come back to the airport and the propeller stopped turning completely. He then declared an emergency, checked that the landing gear was still down and locked, and after seeing traffic on a nearby roadway, performed a forced landing to a grassy area next to a sidewalk that looked clear. The airplane struck a fence during the forced landing and the airplane’s fuselage and wings were substantially damaged. A witness who observed the pilot preparing his airplane at the departure airport for the flight reported that he did not witness the pilot sump either wing fuel tank for water despite the aircraft “being parked for at least a month or two.” Later, as the airplane was going into a nose-up attitude after the touch-and-go, he heard the engine back firing as it was making a shallow left turn. Postaccident examination of the wreckage revealed no evidence of any preimpact mechanical failures or malfunctions of the airframe or engine that would have precluded normal operation. However, water was found throughout the fuel system, including in the left and right fuel tanks, the fuel selector valve sump drain/strainer, the fuel distribution manifold, and the fuel servo. A sample of fuel from the fuel truck used to service the airplane before the accident flight showed no evidence of water or contamination. Since the airplane was serviced with 40 gallons of fuel before the flight, and the pilot reported that the airplane had 40 gallons of fuel on board at takeoff, it is likely that the airplane would have had little to no fuel in the tanks before being refueled. Accordingly, the water present was likely the result of condensation in the fuel tanks, which can happen inside a less-than-full fuel tank when a temperature difference occurs between the walls of the fuel tank and the air in the tank, causing water droplets to form on the inside of the tank. This accumulation of water within the fuel system was not detected by the pilot during his preflight inspection and likely resulted in the loss of engine power.

Quoted verbatim from the NTSB record.