AFJROTC Commercial and General Aviation Take Off Practice Exam

The most common type of aviation fuel used in general aviation aircraft is 100LL (low lead) avgas. This fuel is specifically designed for piston-engine aircraft which dominate the general aviation sector. The "100" in 100LL indicates its octane rating, which is crucial for preventing engine knocking during high-performance operations. The "LL" stands for low lead, referring to a reduced amount of tetraethyl lead added to the fuel, which is a necessary component for enhancing engine performance but has been limited due to environmental concerns.

100LL is widely preferred because it provides the necessary performance characteristics required by most general aviation piston engines while complying with regulatory requirements regarding lead content. This fuel's composition allows it to operate efficiently at various altitudes and conditions that general aviation pilots encounter, making it a reliable choice for training and recreational flying.

In contrast, Jet A fuel is primarily used in turbine-engine aircraft, which are not typical in general aviation settings. 80 octane avgas, while previously common, has become less prevalent due to the shift towards 100LL for its better performance and compatibility with modern aircraft engines. Diesel fuel is not typically used in general aviation because most general aviation aircraft are not designed to run on it. Therefore, 100LL