Piper J3C-65 N70108 accident near Kingsland, Texas

Probable cause

The pilot’s failure to maintain adequate airspeed following a partial loss of engine power resulting from an engine intake valve that became stuck open. Contributing to the accident was the pilot’s decision to operate the airplane when a required maintenance inspection was overdue. Contributing to the severity of the pilot’s injuries was his decision to operate the airplane without using the installed shoulder harness restraints.

NTSB analysis

Witnesses indicated that the airplane was climbing slowly in a nose-up attitude during the initial climb. They noted a slow forward speed and that the engine did not sound like it was operating at full power. The airplane had climbed to an altitude of about 125 feet above ground level and then suddenly rolled to the left and descended in a nearly vertical attitude and impacted terrain on the left side of the runway. The airplane was equipped with a 4-point shoulder harness installation; however, the pilot was using only a lap belt restraint system. Records showed that the airplane had been flown only once in the past year and that the required annual inspection was overdue.

A postaccident examination of the engine showed that corrosion and oil glazing were present and the intake valve on the No. 1 cylinder was stuck in the open position. Based on the available evidence, it is likely that the No. 1 cylinder intake valve was stuck open and resulted in a partial loss of engine power.

Text from the NTSB. Open the NTSB docket for CEN12FA616 for the full record.