Accident Overview
On July 6, 2023, at 0917 Pacific daylight time, a Cessna 182N, registration N703Z, was substantially damaged when it crashed near Jack A Buell Airport (S72), Saint Maries, Idaho. The pilot, who was the sole occupant, was fatally injured. The airplane was being operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
Flight History
The pilot intended to fly to Pierce County Airport (PLU) on a cross-country flight. Witnesses at or near S72 observed the airplane take off from runway 10 and noted it was not gaining altitude. They reported seeing smoke and hearing the engine making “sputtering” and “popping” sounds. The airplane then turned and spiraled down into a field. One witness stated that the flaps were still extended when the airplane turned left and descended.
ADS-B data showed the airplane departed runway 10 at 0916:59, reaching a maximum altitude of 240 ft above ground level (agl) at 0917:28 at a groundspeed of 61 knots. The track indicated the airplane continued in the direction of travel for another 4 seconds, then began a slight left turn with decreasing groundspeed. The last recorded data at 0917:41 showed the airplane at 45 ft agl and 44 knots groundspeed. The accident site was 1,320 ft from the last ADS-B target on a bearing of 095°.
A security camera east of the departure runway captured video showing the airplane left-wing-low in a near-vertical descent just before impact. A public audio streaming service recorded CTAF transmissions; the pilot transmitted he was taking off and shortly thereafter announced “failure.”
Aircraft and Engine Information
The airplane was equipped with a Continental O-470S, 6-cylinder engine, the original engine installed at manufacture. It was overhauled in March 2004, approximately 935 operating hours before the accident. The last annual inspection was in May 2023, about 15 hours before the accident. The maintenance logbook did not document engine compression at that time.
Per Continental Motors, the recommended time between overhaul for the O-470-N is 1,500 hours or 12 years. At the time of the accident, the engine had 935 hours since the last overhaul, which had occurred 19 years prior.
Wreckage and Impact
The airplane came to rest in a nose-down attitude on a heading of about 252° in a flat hayfield with soft dirt and 4- to 5-ft-tall dry grass. The site was about 2,120 ft from the departure end of runway 10. Powerlines ran parallel and perpendicular about 2,070 ft from the runway end. The first identified point of impact was the left outer composite wing tip structure and a section of the wing spar embedded about 6 inches in the ground. The clear lens had broken off, and fiberglass fragments were found 10 ft east of the main wreckage.
The main wreckage consisted of wings partially attached to the fuselage with extensive crush damage and rearward accordion folding. Both left- and right-wing fuel bladders had ruptured; both fuel caps were in place. The instrument panel and cockpit were crushed and comingled, covering the engine and propeller, which were embedded in the ground. The horizontal stabilizer, elevator, and vertical stabilizer remained attached to the empennage, which was partially separated and remained attached by sheet metal and flight control cables. The tail section near the aft baggage area was folded down over the right wing.
Engine Examination
Examination revealed that the head of the No. 3 cylinder exhaust valve had separated from its stem and was stuck in the valve guide. The piston crown had separated from its wrist pin and was damaged within the barrel; the intake pushrod and tube were bent. Metal fragments including piston skirt particles were found in the oil sump.
Components from the No. 3 cylinder were sent to the NTSB Materials Laboratory. The exhaust valve head fracture surface was completely obliterated, preventing determination of fracture mechanism. The exhaust valve fracture initiated at the stem’s core and propagated to the edges with final separation at the shear lip. SEM images revealed cyclic overstress features near the shear lip. The valve stem exhibited thermal discoloration that remained after cleaning. Small gouges and wear marks were found on the exhaust valve stem surface near the rotocoil.
The top of both valve stems were examined for wear markings. The intake valve top showed no visible wear marks, while the exhaust valve top showed significant wear in the form of material deformation cupping over to the outside surface of the chamfer.
Average stem diameter measured 0.0023 inches below specification, and chromium coating was missing along some areas. The exhaust valve guide bore measurements exceeded specifications, with the reading near the bottom of the bore more than 0.03 inch greater.
Previous Maintenance
For unknown reasons, in January 2008 the No. 2 exhaust valve was lapped and staked, in March 2009 the No. 2 cylinder valve guide was replaced, and in June 2015 the No. 1 cylinder was replaced.
Recording Devices
A Shadin fuel flow indicator and Stratus 3i Appareo device were examined by an NTSB Recorders Specialist. Both were in good working condition. The Shadin indicated 77.2 gallons of fuel remaining. The Stratus 3i recorded the final moments of flight.
Pilot Medical Information
The pilot’s last aviation medical examination was on July 1, 2022. The pilot reported a medical history of prediabetes, high blood pressure, and gout. Medications were FAA-approved, and the pilot was issued a third-class medical certificate with a limitation for near-vision glasses.