The pilot reported that, during cruise flight, he observed that the engine would not advance past 2,100 rpm, which was 300 rpm below the RV-7’s normal cruise power setting.
The pilot’s attempts to troubleshoot the engine issue were unsuccessful, and he chose to conduct a precautionary landing near Bartow, Georgia. Shortly after, the oil temperature increased, and oil covered the windshield.
During the precautionary landing on a dirt road, the left wingtip hit the ground and the airplane cart-wheeled, which resulted in substantial damage to the wings and rudder.
After the accident, about 10 gallons of 90-octane automotive gasoline (auto gas) were drained from the airplane.
According to a service letter issued by the engine manufacturer, “Use of lower-than-specified octane fuel could cause detonation and mechanical damage to the engine.”
The service letter did not list 90-octane auto gas as an approved fuel for use in the accident engine.
Examination of the engine also revealed significant thermal damage to the No. 1 cylinder, piston, and rings consistent with detonation, which likely resulted from the pilot’s use of the improper fuel grade for the engine.
Probable cause: The pilot’s use of the improper fuel grade for the engine, which resulted in detonation, engine damage, and loss of engine power.
NTSB Identification: ERA15LA205
This May 2015 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.