FAA Warns STC Holders About Ethanol in Auto Fuel

November 1, 2006 – The FAA has issued a Special Airworthiness Information Bulletin (SAIB), warning aircraft owners and operators with auto fuel supplemental type certificates to ensure the fuel they use does not contain alcohol (ethanol or methanol). The SAIB reinforces EAA?s ongoing efforts to ensure availability of compliant autogas by heading off or modifying legislative attempts in several states to require ethanol in all gasolines sold. EAA, one of two primary sources of automobile gasoline STCs for general aviation aircraft, advocates that at the very least, states should exempt premium grade fuel from ethanol mandates to ensure a readily available and safe fuel supply for aircraft. The FAA cites numerous reasons that alcohol and airplanes do not mix. Alcohol:

  • Adversely affects the volatility of auto gasoline, which could cause vapor lock.
  • Is corrosive and not compatible with the rubber seals and other materials used in aircraft, which could lead to fuel system deterioration and malfunction.
  • Is subject to phase separation, which happens when the fuel is cooled as an aircraft climbs to higher altitudes. When the alcohol separates from the gasoline, it may carry water that has been held in solution and that cannot be handled by the sediment bowl.
  • Reduces the energy content of the fuel. Methanol has approximately 55 percent of the energy content of gasoline, ethanol 73 percent. More alcohol equals reduced range.

EAA’s auto fuel STC has saved aircraft owners untold thousands of dollars by allowing them to use unleaded auto fuel rather than more expensive avgas. FAA recommends that owners use automobile gasoline that conforms to the specifications published in their airplane flight manual or automobile gasoline STC flight manual supplement. Those unsure about the presence of alcohol can perform a simple test, outlined in the SAIB. EAA’s auto fuel Alcohol Test Kit is available for this purpose.

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