Cessna R172 N3FR accident near Rocky Mount, North Carolina

Probable cause

The pilot and mechanic’s failure to identify and completely eliminate the water and debris contamination present in the airplane’s fuel system before embarking on the flight, which resulted in a total loss of engine power.

NTSB analysis

The airplane had not been used for 2 years following an engine overhaul. A mechanic completed an annual inspection of the airplane, and when he and the pilot performed a preflight inspection before beginning the multi-leg trip, they found that the fuel contained, “a lot of water.” They fully fueled the airplane, allowed it to settle overnight, and then “shook” the airplane’s wings before sampling fuel. They also ran the airplane’s engine for two hours on the ground before departing on the first leg of the trip. At the next fuel stop, they drained about “a tablespoon” of water from the fuel system, and during the second fuel stop, they only observed about “2 drops” of water. The accident flight was the third leg of the trip. After nearly 3 hours of flight, and while descending to the destination airport with the carburetor heat applied, the engine lost total power. The pilot established best glide speed and attempted to restore engine power; however, he was unsuccessful and performed a forced landing onto a city street, substantially damaging the fuselage, empennage, and both wings.

Postaccident examination of the engine revealed that one of the cylinders exhibited excessive piston-to-cylinder clearance, circumferential markings of the cylinder walls that were not consistent with the typical cross-hatching pattern that would be expected in an engine shortly after overhaul, and its intake valve was stuck open. While anomalous, each of these findings could reasonably be associated with some partial loss of engine power, but not the complete loss of engine power that was described by the pilot during the descent phase of the accident flight.

The examination of the airframe also revealed rust around the fuel filler ports, indicative of water entry into the airplane’s fuel tanks. While fuel recovered from the left wing fuel tank was free from contaminants, significant water and debris were observed in fuel recovered from the gascolator and carburetor bowls. Given this information, it is likely that the total loss of engine power was due to contamination of the fuel supply with water and particulate matter.

Text from the NTSB. Open the NTSB docket for ERA24LA179 for the full record.