Cessna 172S N184NW accident near Traverse City, Michigan

Probable cause

The failure of maintenance personnel to properly torque a fuel line “B” nut, which resulted in a total loss of engine power.

NTSB analysis

The pilot receiving instruction was on a visual approach to the runway during an instructional flight, at which time the engine lost total power. The flight instructor took control of the airplane and made multiple attempts to restart the engine, which were unsuccessful. The flight instructor declared an emergency and executed a forced landing to a park area about 1 mile north of the runway. During the forced landing, the airplane impacted terrain and a perimeter fence.

Postaccident examination of the airplane revealed substantial damage to the right wing and engine mount. Examination of the engine and fuel system revealed a loose “B” nut fitting on the fuel line between the fuel injector and fuel manifold. The engine had recently been installed by maintenance personnel; the airplane had flown about 2.7 hours after the installation and before the accident. There was no visible impact damage to the “B” nut on the line or the fitting. Given this evidence, the “B” nut on the fuel line was likely not properly tightened during engine installation, which allowed the nut to loosen with normal engine vibration and allowed air to enter the system which resulted in total loss of engine power.

Text from the NTSB. Open the NTSB docket for CEN22LA194 for the full record.