The FAA finally has taken notice of the potential problems posed by ethanol to users of automobile gasoline in airplanes.
The Experimental Aircraft Association and many aviation publications, including this one, have been warning pilots flying on ‘mogas’ about the hazards of ethanol – a form of alcohol – for several years.
In a Special Airworthiness Information Bulletin issued last month, the agency explained that, although ethanol may be appealing to environmentalists, it is destructive to airplane engines and many of their critical parts.
Increasingly, ethanol is being mandated by states as a substitute for the environmentally unfriendly chemicals MTBE and ETBE in automobile gasoline.
Modern automobile engines are built to use fuels containing up to 10% ethanol, but aircraft engines are not.
Alcohol is highly corrosive to the rubber seals and tubing used in aircraft fuel systems and, as it produces substantially less energy per pound than gasoline, it reduces the amount of power available from fuel containing it.
Alcohol also increases the risk of vapor lock and, being hygroscopic, is likely to introduce water into the fuel system, particularly as it cools at higher altitudes.
The FAA’s SAIB states unequivocally that users of engines STC’d for automobile gasoline must either find alcohol-free fuel or switch back to 100LL.
While there is a federal requirement for pumps dispensing fuel containing alcohol to be labeled, not all such labels are obvious. The SAIB offers a simple test that anyone can perform to determine – before buying it – whether there is alcohol in fuel, and test kits are available from the EAA and other sources.
— Thomas F. Norton