Piper PA28 N3568K accident near Bonifay, Florida

Probable cause

A partial loss of engine power due to a stuck exhaust valve. Contributing to the accident was the pilot's decision to operate an airplane with a known mechanical deficiency and his failure to fly an appropriate traffic pattern that would have allowed the airplane to reach the runway.

NTSB analysis

The owner of the airplane experienced a partial loss of engine power during takeoff following a touch-and-go landing, but was able to complete a 180° turn and land safely back on the runway. During a post-landing engine run-up, the owner was unable to duplicate the problem, so he taxied to his hangar and reported the problem to his mechanic. The mechanic, a commercial pilot, subsequently boarded the airplane, performed an engine run-up, which seemed normal, and elected to fly the airplane around the airport traffic pattern. A witness, who heard and saw the airplane on final approach, stated that the engine was making "small explosions" or "backfire"-like sounds. The airplane subsequently collided with a tree before it impacted the ground and a fence short of the 4000-foot-long runway and was consumed by a postcrash fire.

Examination of the airplane revealed that the No. 4 cylinder exhaust valve was stuck in the "open" position due to excessive deposits from the combustion process. It is likely that the stuck exhaust valve resulted in the partial loss of engine power. Maintenance records revealed that the engine had not been inspected in accordance with a manufacturer service bulletin regarding stuck valves. Had the service bulletin been complied with, it is possible that the accident may have been prevented. Despite the partial loss of engine power that occurred during the previous flight, the pilot flew a traffic pattern that resulted in the airplane descending into trees about 1/4 mile before the runway threshold after the airplane experienced a partial loss of engine power during the accident flight.

The pilot was diabetic, and although his blood glucose was likely not very elevated at the time he died, it was somewhat elevated on average over the preceding few weeks. Elevated blood glucose can cause blurred vision and subjective sensation of fatigue, as well as increased thirst and urination. Unless life-threatening, it does not directly impair decision-making or judgment; thus it is unlikely that the pilot's diabetes contributed to the circumstances of this accident.

Text from the NTSB. Open the NTSB docket for ERA18FA084 for the full record.