Garlick UH-1B N46969 accident near Kettle Falls, Washington

Probable cause

A total loss of engine power due to foreign object (towel) ingestion. Contributing to the accident was maintenance personnel’s inadequate postmaintenance inspection of the engine.

NTSB analysis

The commercial pilot was conducting an external load logging flight in the helicopter. A review of maintenance records revealed that, on the day of the accident, the engine had been replaced with an overhauled engine. Following the maintenance, the pilot completed one logging cycle without incident. The pilot reported that, about 50 minutes into the second cycle, she heard a loud screeching/grinding noise followed by a muffled "bang." The low rotor rpm horn sounded, and she initiated an autorotation. The helicopter touched down, impacted trees, rolled down sloped terrain, and then came to rest.

A postaccident examination of the engine's particle separator assembly revealed that it was intact and installed properly on the air inlet section; however, the inlet guide vanes exhibited signatures consistent with foreign object damage, and a material consistent with a towel was found within the vanes. Given the damage signatures and the found material, it is likely that maintenance personnel did not adequately inspect the engine area after installing the overhauled engine and left a towel in its compressor section, which the engine subsequently ingested and resulted in a total loss of power.

Text from the NTSB. Open the NTSB docket for WPR15LA159 for the full record.