Under what conditions may automobile gasoline be used in an aircraft engine?

Using automobile gasoline in an aircraft engine is permissible only if it has received explicit approval from the FAA through a Supplemental Type Certificate (STC). This certification ensures that the use of automotive fuel meets specific safety and performance standards for that particular aircraft model. STCs are regulatory approvals that signify that the aircraft's design, including its fuel system and engine, can safely operate using the alternative fuel without compromising the aircraft's safety or performance.

The necessity of an STC is grounded in the rigorous safety and performance requirements that govern aviation standards. Aircraft engines are designed and tested using specific fuel types, and using an unapproved fuel could result in engine malfunction or failure, jeopardizing flight safety. The FAA’s oversight through an STC guarantees that changes to fuel types have been thoroughly assessed.

This careful regulatory approach differs significantly from situations where fuel might simply be chosen based on convenience or scarcity, as would occur if considering the other options. For example, the idea of using automotive fuel merely because it is available or at the pilot's discretion disregards the substantial technical and safety implications associated with introducing a non-approved fuel into aviation operations.