What happened
On September 7, 1986, an aircraft departed for a local hunting trip carrying a client. The flight did not return to its origin point, and the wreckage was eventually located on September 9, 1986. Upon discovery, the airplane was found to be destroyed by post-impact fire.
The investigation
An examination of the incident revealed critical details regarding the aircraft's operation prior to the crash. According to a guide for whom the pilot was working, the airplane had been operating using unleaded automotive fuel. A subsequent engine teardown analysis indicated that the powerplant sustained only impact and fire damage, providing no evidence of pre-impact mechanical failure.
Findings
The use of unleaded automotive fuel in an aircraft engine is a significant factor in this accident. Aviation engines are specifically designed to operate with high-octane aviation gasoline (avgas), which contains lead to protect valve seats and provide necessary lubrication and anti-knock properties. Using unleaded automotive fuel can lead to severe engine malfunctions, including pre-ignition, detonation, and eventual loss of power due to valve recession or failure.
Safety message
Pilots must ensure that only the correct grade of aviation gasoline is used in their aircraft. The use of automobile fuel in piston-engine aircraft is prohibited and poses a severe risk of engine failure.