What grade of fuel is most commonly used in your training airplane?

The most commonly used grade of fuel in training airplanes is 100LL (Low Lead). This fuel type is specifically formulated for aviation piston engines and is the most prevalent fuel found at flight schools and general aviation airports.

100LL has a higher octane rating compared to 80 octane, which makes it suitable for engines that require better performance and detonation resistance, especially when operating under higher power settings or in warmer temperatures. The "LL" designation indicates that this fuel contains only a small amount of tetraethyl lead, reducing environmental and health hazards associated with lead exposure while still providing the necessary performance characteristics for most training aircraft.

In contrast, 80 octane is generally used in older aircraft or those with lower power requirements, while 100 octane and 123 octane are not standard aviation fuels and are not typically used or found in training environments. Therefore, 100LL is the clear choice as the fuel grade most frequently used in training airplanes.