Cessna 177RG N52156 accident near Grass Valley, California

Probable cause

An improperly tightened B-nut fitting at the fuel flow divider, which resulted in a fuel leak and loss of engine power due to fuel starvation, and the inadequate maintenance inspection, which failed to detect and correct the discrepancy.

NTSB analysis

The airplane entered the airport traffic pattern, and,.shortly after turning onto the left base leg, the pilot transmitted on the common traffic advisory frequency (CTAF) that the airplane had lost all engine power. The pilot then discontinued the base-to-final turn and instead turned the airplane away from the airport likely in an attempt to land in an open area. The airplane subsequently struck 60-ft trees, which separated the stabilator, then descended uncontrolled to the ground adjacent to the road.

Fuel was recovered from the wreckage, and a postaccident examination of the engine revealed that the B-nut fitting on the inlet line into the fuel flow divider was over 1/2 a turn loose, and the area surrounding the B-nut fitting exhibited blue dye staining, consistent with fuel leakage. No impact damage to the B-nut on the line or to the fitting on the fuel flow divider was observed, and there was no evidence of any other preimpact anomaly that would have precluded normal engine operation.

It is likely that the B-nut fitting on the inlet line to the fuel flow divider was not properly tightened, which allowed it to continue to loosen due to normal engine vibration, resulting in fuel leakage from the fitting and insufficient fuel delivery to the engine (fuel starvation). Further, data from the engine data management system indicated that the engine was running normally until the last few seconds of the flight. The data showed that, during those final seconds, the cylinder head temperatures (CHTs) and exhaust gas temperatures (EGTs) for all four cylinders spiked briefly before dropping rapidly, consistent with a loss of engine power due to fuel starvation.

The airplane’s last annual inspection was completed 10 days before the accident, and, since then, the airplane was operated for about 2.5 hours (including the accident flight). Per the applicable regulation, annual and 100-hour inspections, “Each person performing an annual or 100-hour inspection shall inspect engine lines, hoses, and clamps for leaks, improper condition, and looseness.”

Text from the NTSB. Open the NTSB docket for WPR25FA146 for the full record.