On November 14, 1988, a Ryan NAVION A (registration N5164K) operated by Blaine K. Fennell was involved in an aviation accident near Franklin, PA. Investigators recorded the probable cause as: DUE TO IMPROPER GRADE OF FUEL IN THE AIRPLANE AND BENT AND BINDING EXHAUST VALVES, THE AIRPLANE ENGINE HAD A PARTIAL LOSS OF POWER DURING THE TAKEOFF GROUND RUN. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
Witnesses reported hearing engine sputtering and backfire during a slow takeoff. The aircraft descended behind trees. Post-accident inspection found auto gas in the fuel system, no supplemental type certificate for its use, and multiple exhaust valve issues.
Event Description
Witnesses observed the aircraft during takeoff ground run, noting that the engine sputtered and backfired. The takeoff roll was described as long and slow. As the aircraft passed the terminal building, it was in a slow-speed, high-pitch attitude, and the engine RPM appeared to decrease. Subsequently, the aircraft descended behind a line of trees.
Post-Accident Inspection
Following the accident, investigators examined the aircraft. The fuel system contained auto gas, and no Supplemental Type Certificate (STC) authorizing the use of auto gas was found for the aircraft. Inspection of the engine revealed several exhaust valve anomalies:
The #2 exhaust valve was visibly warped.
The #3 exhaust valve guide was broken and moved with the stem upon removal.
The #4 exhaust valve was tight in its guide.
Compression testing showed that the #2 cylinder had zero compression.