Airframe Mechanic Certification Aircraft Fuel Systems 2 — Questions and Answers
Question 1: What material is commonly used for flexible fuel hose connections in certified aircraft fuel systems?
- Copper tubing
- Aluminum rigid tubing
- Teflon-lined synthetic rubber hose (Correct answer)
- Unlined steel braided hose
Correct answer: Teflon-lined synthetic rubber hose
Teflon-lined synthetic rubber hoses are used for flexible fuel connections because Teflon resists aviation fuel degradation and the rubber provides flexibility to absorb vibration.
Question 2: Where should a fuel tank sump drain be located to be most effective?
- At the highest point of the tank to allow air to escape
- At the lowest point where water and sediment accumulate (Correct answer)
- At the midpoint of the tank sidewall for access
- Adjacent to the fuel quantity transmitter
Correct answer: At the lowest point where water and sediment accumulate
Sump drains are at the lowest point so water, which is denser than fuel, and sediment collect there and can be drained during preflight inspection.
Question 3: What is the purpose of a fuel cross-feed system on a multi-engine aircraft?
- To allow fuel flow from one wing tank to the other or to feed any engine from any tank (Correct answer)
- To remove dissolved air from fuel lines
- To return excess fuel to the main tank after engine shutdown
- To boost fuel pressure during high-power takeoff
Correct answer: To allow fuel flow from one wing tank to the other or to feed any engine from any tank
A cross-feed system allows fuel to be transferred between tanks for lateral balance or to supply any engine from the opposite wing tank in the event of a fuel pump failure.
Question 4: Under what conditions may automotive gasoline (mogas) be used in a certificated aircraft?
- Any time it has the same octane rating as the specified avgas
- Only when the aircraft has an STC specifically approving its use (Correct answer)
- Always acceptable as an emergency substitute for avgas
- It may be mixed freely with avgas without restriction
Correct answer: Only when the aircraft has an STC specifically approving its use
Automotive gasoline may only be used in certificated aircraft when a Supplemental Type Certificate (STC) has been issued specifically approving mogas for that aircraft and engine combination.
Question 5: What is the maximum allowable fuel tank leakage per FAA standards?
- Zero leakage is permitted under any condition
- Seepage (wetness without drops forming) is acceptable; dripping is not (Correct answer)
- Up to three drops per minute is acceptable during normal operation
- Any minor leakage is acceptable if the fuel cap is secure
Correct answer: Seepage (wetness without drops forming) is acceptable; dripping is not
FAA standards distinguish between 'seepage' (fuel wetness with no drops) which is acceptable, and 'leakage' where drops form, which is not airworthy.
Question 6: What is the purpose of fuel tank baffles installed inside aircraft fuel tanks?
- To increase internal fuel tank pressure during climb
- To prevent fuel surge and maintain fuel outlet coverage during flight maneuvers (Correct answer)
- To filter large debris before fuel reaches the boost pump
- To allow the fuel quantity transmitter to read accurately
Correct answer: To prevent fuel surge and maintain fuel outlet coverage during flight maneuvers
Fuel tank baffles are internal partitions that prevent fuel from surging away from the outlet during maneuvers, ensuring continuous uninterrupted fuel flow to the engine.
Question 7: What type of fuel system is used on most high-wing general aviation aircraft with gravity-fed carburetor engines?
- Pressure injection system with electric pumps
- Gravity-feed system relying on fuel head pressure from the tanks (Correct answer)
- Bladder-cell system pressurized by engine bleed air
- Centrifugal pump system driven by the accessory gearbox
Correct answer: Gravity-feed system relying on fuel head pressure from the tanks
High-wing aircraft with carbureted engines often use a gravity-feed system where fuel flows by gravity from the wing tanks above the engine without requiring a pump.
Airframe Mechanic Certification Aircraft Fuel Systems 2
What material is commonly used for flexible fuel hose connections in certified aircraft fuel systems?