Cessna 182N N703Z accident near St Maries, Idaho

Probable cause

The total loss of engine power due to the failure of the No. 3 exhaust valve for reasons that could not be determined. Contributing to the accident was the pilot’s failure to maintain control of the airplane after the loss of engine power.

NTSB analysis

Shortly after takeoff, the airplane lost engine power and the pilot transmitted “failure” over the Common Traffic Advisory Frequency (CTAF). Witnesses reported hearing the engine popping and sputtering and seeing smoke coming from the airplane. They reported the airplane turned and descended to impact with the terrain. ADS-B data indicated the airplane reached a maximum altitude of 240 ft before it descended to impact a hay field about 0.5 nautical miles from the departure end of the runway.

Postaccident examination revealed that the No. 3 engine cylinder exhaust valve head was separated from its stem. The exhaust valve fractured at its neck in cyclic brittle overstress initiating at the stem’s core and propagating to the edges, with the final separation at the shear lip.

The valve stem and guide exhibited excessive wear and thermal discoloration. It could not be determined if this was due to operational wear or if the valve guide or stem was built to specification at the time of assembly.

Although the engine had only 935 hours total time (565 hours short of the recommended overhaul period) it was 19 years since the last overhaul. Teledyne Continental Motors Service Information Letter SIL98-9C states the time between overhaul for the IO-470 series engines is 1,500 hours or every 12 years, whichever occurs first. Following manufacturer overhaul periods is not required for Part 91 operations. However, since the last overhaul in 2004, the Nos. 1 and 2 cylinders were repaired, including replacement of the No. 2 valve guide.

Text from the NTSB. Open the NTSB docket for WPR23FA256 for the full record.