Airframe Mechanic Certification Aircraft Fuel Systems 1 — Questions and Answers
Question 1: What type of fuel is used in most modern turbine-powered aircraft operating in the United States?
- Aviation gasoline (avgas) 100LL
- Jet-A (Correct answer)
- JP-4
- Mogas
Correct answer: Jet-A
Jet-A is the standard turbine fuel used in commercial and general aviation jet aircraft in the US due to its consistent flash point and energy content.
Question 2: What is the primary purpose of a fuel boost pump in an aircraft fuel system?
- To filter contaminants from the fuel
- To provide positive fuel pressure and prevent vapor lock (Correct answer)
- To measure fuel quantity in the tank
- To transfer fuel between wing tanks
Correct answer: To provide positive fuel pressure and prevent vapor lock
Fuel boost pumps supply positive pressure to the engine-driven fuel pump inlet, preventing vapor lock and ensuring reliable fuel flow especially at high altitudes.
Question 3: What color dye is used to identify 100LL aviation gasoline (avgas)?
- Red
- Green
- Blue (Correct answer)
- Purple
Correct answer: Blue
100LL (low lead) avgas is dyed blue so it can be visually distinguished from other fuels, preventing misfueling during servicing.
Question 4: What is the function of a fuel strainer (gascolator) installed in an aircraft fuel system?
- To boost fuel pressure to the carburetor
- To remove water and debris from fuel before it reaches the engine (Correct answer)
- To measure fuel flow rate to the engine
- To control the fuel-to-air mixture ratio
Correct answer: To remove water and debris from fuel before it reaches the engine
A fuel strainer or gascolator filters out water, sediment, and particulate contaminants to protect the carburetor and engine from damage.
Question 5: What fuel tank venting requirement must be met to prevent structural damage to the tank?
- Vents must be located only on the top surface of fuel tanks
- Vent openings must be protected against ice blockage (Correct answer)
- All vents must incorporate check valves
- Vents must allow airflow in one direction only
Correct answer: Vent openings must be protected against ice blockage
FAA regulations require fuel tank vents to be protected against icing so tanks can breathe freely, preventing dangerous pressure differentials that could damage the tank structure.
Question 6: What does the term 'unusable fuel' mean in the context of an aircraft fuel system?
- Fuel that has been contaminated and cannot be used safely
- Fuel that cannot be safely used in flight due to system design limitations (Correct answer)
- Aviation fuel that has exceeded its storage shelf life
- Fuel remaining in lines after the engine is shut down
Correct answer: Fuel that cannot be safely used in flight due to system design limitations
Unusable fuel is the quantity that cannot be safely delivered to the engine in all normal flight attitudes due to outlet location and tank geometry.
Question 7: What fuel selector valve position is recommended during takeoff and landing on most aircraft with multiple fuel tanks?
- Off
- Left tank only
- Both tanks or the fullest tank (Correct answer)
- Right tank only
Correct answer: Both tanks or the fullest tank
Selecting 'Both' or the fullest tank during takeoff and landing ensures maximum fuel availability and minimizes the risk of fuel starvation during these critical flight phases.
