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STC Compliance

REVISED 10/17/11

EAA STC approvals are for the use of unleaded regular automobile gasoline, excluding gasoline containing alcohol, manufactured to the ASTM Specification D-4814 (American Society of Testing Materials, 1916 Race St., Philadelphia, PA 19103). Specification D-4814 superseded Specification D-439.

According to FAA Advisory Circular 23.1521-1B, "Automobile gasoline not containing alcohol or other oxygenates, conforming to D-439 and D-4814 are essentially identical and may be used interchangeably." (Most STC's still read "D-439.") Specification D-4814 added the definitions and requirements for the use of alcohol and ether additives.

In most states, the law requires compliance with D-4814 or its equivalent. Major fuel suppliers, those who generally have their name on the product from well head to retailer, can be expected to comply since this is a rather broad specification and in wide use. The Department of Energy Reports, which are issued twice a year, show that most fuel in the United States conforms completely to the specification requirement, and in those cases where there is some excursion, it is in non-critical areas. For example, the octane requirement for most regular automobile gasoline is 82; however, even though some automobile gasoline has tested lower than 82 octane, no automobile gasoline has tested lower than 80 octane.

If further reassurance is necessary, a sample of gasoline to be used can be taken to a state testing lab, or a state university to obtain a chemical breakdown to confirm compliance with the specification. There is usually a nominal fee.
Product exchange arrangements among oil companies require conformance to at least D-4814 specification requirements. It simply is not practical for oil companies to market nonconforming fuels in a limited market area.

Gasoline manufacturers have internal specifications, which are more restrictive than ASTM specifications, to ensure meeting these requirements which represent minimum characteristics of automobile gasoline. The following is a list of 38 states in 2011 requiring compliance with ASTM D-439/D-4814 in whole or in part for the sale of automobile gasoline within the states, and also states that require critical specification values. The source of this information is, "The Impact of U. S. Environment Regulations on Fuel Quality" issued by ASTM. For the most current information, contact ASTM. Your library will have the address of the closest office.

Revised 10/17/2011






Rhode Island



South Carolina



South Dakota














New Hampshire



New Mexico

West Virginia


New York



North Carolina



Ohio- Summit County Only


As with any Supplemental Type Certificate, there is a requirement for an aircraft mechanic to inspect the aircraft to ensure compliance with the terms of the STC, and an IA mechanic must execute FAA Form 337 for both the airframe and engine and forward this to the FAA. At the present time, there are no requirements for mechanical changes in either the airframe or the engine, to use automobile gasoline. However, changes are required for modifying the Lycoming O-235-L2C and -K2C to lower the compression ratio and reduce the 100 octane rating to 80, thus permitting the use of automobile gasoline. This must be done under a separate STC, which is included with the STC for this engine installation.

The EAA's type certification test program has resulted in FAA approval for nearly all 80 octane Teledyne Continental Motors engines, from the A-40 up through the O-470, and most Lycoming engines from the O-235-C series through the O-540-B series. It should be recognized that in some aircraft where fuel systems are complex and have characteristics which may lead to vapor formation with higher volatility automobile gasoline, there may have to be changes made in the fuel delivery system to permit safe operation with this fuel. Engineering flight tests are needed to determine what changes, if any, are required for specific aircraft applications.

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