Cessna 172 N7137T accident near Skwentna, Alaska

Probable cause

A partial loss of engine power due to detonation/preignition damage to the No. 2 cylinder. The reason for the detonation/preignition damage could not be determined based on the available evidence.

NTSB analysis

The pilot reported that during takeoff from an off-airport gravel bar on a river, the airplane experienced a partial loss of engine power. The pilot rejected the takeoff, and the airplane subsequently encountered a “bump,” which pitched the nose down. The pilot then made a hard right turn to avoid going into the water, and the airplane nosed down and impacted the ground with the left wing, which resulted in substantial damage to the left wing.

Postaccident examination revealed that the No. 2 cylinder would not produce compression. Removal of the No. 2 cylinder revealed damage, including a hole in the piston that was consistent with detonation and/or preignition. The reason for the detonation and/or preignition could not be determined based on the available evidence.

Text from the NTSB. Open the NTSB docket for ANC21LA061 for the full record.