Cessna 172RG N6386V accident near Louisburg, North Carolina

Probable cause

Maintenance personnel’s failure to identify and remediate water contamination of the airplane’s fuel system, which resulted in a partial loss of engine power during initial climb.

NTSB analysis

Maintenance personnel had completed an annual inspection of the airplane two days before the accident flight. The pilot reported that during his preflight inspection of the airplane, he observed water contamination when he was sampling fuel from the fuel system, and that he continued to drain fuel samples until he saw no water. The engine start, taxi, run-up and takeoff were uneventful and just after the pilot retracted the landing gear, after which the engine smoothly began losing power, reaching near idle. The pilot decided to land the airplane straight ahead and while gliding he applied full throttle, and the engine briefly revved to about 1,900 rpm before reducing uncommanded again to idle. The airplane subsequently impacted an airport perimeter fence resulting in substantial damage to the horizontal stabilizer.

A postaccident examination of the airplane and engine found no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. The examination also found that the airplane wing fuel tank caps and filler necks exhibited rust and corrosion, a condition that likely degraded the ability of the seals to keep out water and other contamination. Rust-colored granules and/or corrosion were also observed in the carburetor fuel inlet screen and fitting, gascolator and filter, and the internal check valves of the engine driven fuel pump. This was consistent with long-term water contamination of the fuel system. Liquid recovered from the electric fuel pump and fuel strainer was also contaminated with water, indicating that the pilot’s efforts to eliminate water from the fuel system during his preflight inspection were not successful. Fueling records showed the airplane had last been fueled over a year prior to the accident and airport personnel also reported that the airplane had been stored outside at a tiedown since arriving at the airport 19 years prior to the accident.

Data recovered from an engine data monitor revealed that the fuel flow during the accident takeoff roll and initial climb remained relatively constant, and that the exhaust gas temperature readings for all cylinders were erratic. The data monitor did not record engine rpm. The erratic exhaust gas temperature readings with a constant fuel flow indication, and the engine’s partial loss of power during initial climb, were likely the result of water contamination in the fuel system.

A review of maintenance logbooks showed that the airplane had no documented service performed for a 14-year period while being stored outdoors on the airport ramp. Maintenance personnel reported that during the most recent annual inspection, the fuel system was visually inspected, the gascolator bowl and filter were removed and cleaned, and the system was not flushed. Based on the available information, it is likely that the airplane’s fuel system was severely contaminated with water that was likely the result of the airplane’s prolonged outdoor storage combined with fuel tank cap and filler neck degradation that allowed water intrusion into the fuel tanks. While maintenance personnel reported conducting some inspection of the fuel system during the annual inspection that was completed immediately prior to the accident flight, the pilot’s observation of significant water contamination of the fuel system during his preflight inspection, along with water contamination that was found during the postaccident examination of the airplane indicate that the root cause and the impacts of the water contamination on the fuel system had not been adequately identified or remediated.

Text from the NTSB. Open the NTSB docket for ERA25LA188 for the full record.