Using Different Fuel May Void Homebuilt Operation Limitations

July 22, 2018 - Experimental category aircraft owners may not know that any change to a fuel system is considered by the FAA to be a major change and could require re-establishing compliance to the aircraft’s operating limitations. That’s not only adding or removing a fuel pump, but also rerouting fuel lines and adding or removing a fuel tank. It also extends to the fuel itself.

Using a fuel that is not approved as an aviation fuel by the FAA is considered a major change and would require compliance with the major change provisions of the aircraft’s operating limitations. Owners and operators of experimental aircraft are required to operate the aircraft in accordance with those limitations. They are considered to be a part of the aircraft’s airworthiness certificate and must be carried in the aircraft at all times.

A major change is a change that appreciably affects the weight, balance, structural strength, reliability, operational characteristics, or other characteristics affecting the airworthiness of the aircraft, for example changing to a different engine or propeller. When such a change is made, the owner or operator of the aircraft needs to follow the procedure called out in the aircraft’s operating limitations to re-establish compliance with 91.319(b), the regulation that requires the aircraft to be flight-tested before conducting normal operations.

Most builders and pilots are familiar with the initial Phase I flight testing of an experimental aircraft, but many are not aware that an additional flight-test period is required after incorporating a major change. That includes a fuel system change or the use of a fuel not approved as an aviation fuel by the FAA.

Data shows that fuel issues are a major cause of accidents in experimental aircraft, so it is important that proper testing be done when changes are made. That’s important not only for FAA compliance regarding your aircraft’s operating limitations, but also for your own safety.