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.
The octane rating may have had little or nothing to do with it. If it had an intake leak, which would give a lean mixture and therefore high CHT, (beyond red line) or if he had a broken ring which would also create a lot of heat, either of those alone could cause detonation. The rings were “burned through”, so there’s no way to know for sure. Perhaps it would happen sooner on the lower octane fuel than if he had 100 octane, but not necessarily so and by sooner, I mean now, instead of five or ten minutes from now. Our testing in the 1980’s showed no detonation in the Lycoming 180hp 0-360 even on 89.5 AKI. So the 0-360 STC for autofuel was written for 91 in order to give some margin for error. One thing is clear, if he had CHT”s on ALL cylinders he might have noticed a high heat condition and been able to deal with it one way or another before things became catastrophic.
It also doesn’t mention if the aircraft was landed where the Pilot intended. Why the wingtip hit the ground.
Accidents don’t occur until touchdown.
Why, take the chance of damaging an engine with improper fuel. That engine should have shown indications of detonation during the T.O. or even the climb out. The alcohol laced fuel, especially in my state, is even worse. That fuel effects gas mileage and contains absorbed moisture and sells for even more than the old road fuel.
The accident report does not specify what kind of engine
it was. As some engines are meant to run on this grade of fuel.
True it only lists it as ” experimental engine rated at 180 horsepower that resembled a Lycoming O-360A1A reciprocating engine.” It also includes this,”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 rated fuel as an approved automotive fuel for use in this engine.” It was,i would guess,a Lycoming “clone” such as the Superior XP-Engine, this is of course speculation as the report does not state the specific engine, however that there is a manufacturer service letter it does imply an established maker not a one of a kind engine.
As Greg said. Plus the Docket says the pilot admitted to 87 Octane mogas. The Docket also includes the Lyc Mandatory SB which requires minimum of 93 octane fuel for that engine.