FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationEasy
A mechanic is preparing to service a piston-engine aircraft placarded for 100LL fuel. What does the number '100' in the fuel designation '100LL' represent?
- AThe specific gravity multiplied by 100
- BThe minimum flash point in degrees Fahrenheit
- CThe percentage of tetraethyl lead by volume
- DThe fuel's antiknock (octane/performance) rating
Show answer & explanationAnswer & explanation
Correct answer: D. The fuel's antiknock (octane/performance) rating
The number preceding the letters in an aviation gasoline grade (such as 100LL) indicates the fuel's antiknock or performance rating, which reflects its resistance to detonation. 'LL' means low lead content, not related to the numeric rating.
Why the other options are wrong
- A. Specific gravity is unrelated to the fuel grading system.
- B. Flash point is not part of the grade designation.
- C. Lead content is indicated by 'LL' (low lead), not the numeric grade.
Aviation Gasoline Grading
Avgas is graded by an antiknock/performance number that indicates its resistance to detonation under lean and rich mixture conditions.
- 100LL = 100 octane rating, low lead
- Higher numbers indicate greater detonation resistance
- Grade is dyed blue for 100LL identification
Memory trick: '100' fights knock, 'LL' keeps lead low.