Amateur-built RV-7 N364SJ accident near Bartow, Georgia

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 analysis

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 airplane's normal cruise power setting. The pilot's attempts to troubleshoot the engine issue were unsuccessful, and he chose to conduct a precautionary landing. Shortly after, the oil temperature increased, and oil covered the windshield. During the precautionary landing on a dirt road, the left wingtip impacted 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.

Text from the NTSB. Open the NTSB docket for ERA15LA205 for the full record.