Piper PA28 N1697J accident near Salt Lake City, Utah

Probable cause

A partial loss of engine power due to the mechanic’s failure to properly secure the throttle lever locking nut and cotter pin.

NTSB analysis

The pilot was practicing takeoffs and landings when the engine became unresponsive to throttle inputs. He performed a forced landing onto a highway, during which the airplane was substantially damaged. Examination of the engine revealed that the carburetor throttle lever lock nut was finger-tight, and its cotter pin was absent, which likely resulted in the throttle lever intermittently disengaging from the serrated throttle shaft when the pilot manipulated the throttle.

A review of the maintenance log books and an interview with the mechanic revealed that the throttle cable had been removed and subsequently reinstalled onto the carburetor as part of the most recent annual inspection, which was completed about 1 month before the accident. It is likely that, at this time, the mechanic did not install or inadequately installed the cotter pin through the locking nut and bolt.

Text from the NTSB. Open the NTSB docket for WPR19LA065 for the full record.