N703Z

On July 6, 2023, at 0917 Pacific daylight time, a Cessna 182N, N703Z, was substantially damaged when it was involved in an accident near Jack A Buell Airport (S72), Saint Maries, Idaho. The pilot, who was the sole occupant, was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot planned on flying to Pierce County Airport (PLU) on a cross-country flight. Numerous witnesses at or near S72 airport observed the airplane take off from runway 10 and stated the airplane was not gaining altitude. The witnesses saw smoke and heard the engine making “sputtering” and “popping” sounds. Thereafter, they observed the airplane turn and spiral down into a field. (See figure 1.) One witness stated that the flaps were still extended when the airplane turned left and descended to the ground.

A review of the ADS-B data revealed that the airplane departed from 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 showed the airplane remained in the direction of travel for another 4 seconds, then it began a slight left turn with decreasing groundspeed. The last recorded data was at 0917:41, which indicated the airplane was at an altitude of 45 ft agl at a ground speed of 44 knots. The accident site was located 1,320 ft from the last ADS-B target on a bearing of 095°.

Figure 1. Accident Sequence

A security camera located east of the departure runway captured video of the airplane several seconds before the accident. A review of the video showed that the airplane was left-wing-low in a near-vertical descent just before impact. (See figure 2).

Figure 2. Video screenshots

The FAA does not record the CTAF transmissions at S72 airport; however, CTAF audio was being recorded by a public audio streaming service at the time of the accident. The recording captured the airplane’s communication during the takeoff. The pilot transmitted he was taking off and shortly thereafter announced “failure.”

AIRCRAFT AND OWNER/OPERATOR INFORMATION

The airplane was equipped with a Continental O-470S, 6-cylinder engine. It was the original engine installed on the airplane at the time of manufacture, and was overhauled in March 2004, 935 operating hours before the accident. The airplane’s last annual inspection was in May 2023, about 15 hours before the accident. The maintenance logbook did not document engine compression at that time.

WRECKAGE AND IMPACT INFORMATION

The airplane came to rest in a nose-down attitude on a heading about 252° in a flat hayfield, comprised of soft dirt and 4- to 5-ft-tall dry grass. The accident site was about 2,120 ft from the departure end of runway 10. Powerlines were running parallel and perpendicular about 2,070 ft from the end of the runway (see figure 3). The first identified point of impact was the left outer composite wing tip structure and a section of the wing spar, which was embedded in the ground about 6 inches. The clear lens had broken off and fragments of fiberglass were 10 ft east beyond the main wreckage.

The main wreckage consisted of the wings that remained partially attached to the fuselage and exhibited extensive crush damage and rearward accordion folding. Both left- and right-wing fuel bladders had ruptured, and 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 a portion of sheet metal and flight control cables. The tail section that separated near the aft baggage area was folded down over the right wing.

Figure 3. Number 3 cylinder

ENGINE

Examination of the engine revealed that the head of the No. 3 cylinder exhaust valve had separated from its stem (see figure 3) and was stuck in the valve guide. The piston crown had separated from its wrist pin and was lying damaged within the barrel, and the intake pushrod and tube were bent. Metal fragments including piston skirt particles were found in the oil sump.

All components from the No. 3 cylinder assembly were sent to the NTSB Materials Laboratory. Examination revealed that the exhaust valve head fracture surface was completely obliterated, such that no fracture mechanism information could be obtained. The exhaust valve fracture initiated at the stem’s core and propagated to the edges with the final separation at the shear lip. Scanning electron microscope (SEM) images revealed cyclic overstress features in many areas just inside and along the shear lip.

The valve stem exhibited thermal discoloration, with the discoloration remaining after cleaning. Additionally, small gouges and wear marks were found on the exhaust valve stem surface near the rotocoil.

The top of both valve stems, where the rocker arms come in contact, were examined for wear markings. While the top of the intake valve showed no visible wear marks, the top of the exhaust valve showed significant wear in the form of material deformation cupping over to the outside surface of the chamfer.

The average stem diameter measured 0.0023 inches below specification and chromium coating was missing along some areas of the stem. Similarly, the exhaust valve guide bore measurements were larger than the stated specifications, with the reading near the bottom of the bore being more than 0.03 inch greater.

Continental Motors’ recommended time between overhaul for the O-470-N is 1,500 hours or 12 years. At the time of the accident, the airplane had 935 engine hours since the last overhaul, which occurred in March 2004, 19 years before the accident.

The following work was accomplished 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 retained and examined by a NTSB Recorders Specialist. Both electronics were in good working condition. The non-volatile memory in the Shadin indicated the airplane had 77.2 gallons of fuel remaining and the Stratus 3i Appareo recorded the final moments of flight. (See Electronic Devices Specialist Analysis Report in the docket).

MEDICAL

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. The medications being taken by the pilot were approved by the FAA and the pilot was issued a third-class medical certificate with the limitation to have glasses for near vision.