A&P Aircraft Fuel Systems 2 — Questions and Answers
Question 1: What is the hazard of misfueling a piston aircraft with Jet-A fuel instead of 100LL AVGAS?
- Jet-A will cause the fuel tanks to swell and leak
- Jet-A will not ignite reliably in a spark-ignition engine, leading to power loss or engine stoppage (Correct answer)
- Jet-A is too viscous to flow through the fuel lines at ambient temperature
- Jet-A will corrode aluminum fuel tanks within hours
Correct answer: Jet-A will not ignite reliably in a spark-ignition engine, leading to power loss or engine stoppage
Jet-A's high flash point means it will not vaporize or ignite properly in a spark-ignition piston engine, resulting in power loss, rough running, or engine failure.
Question 2: What is the purpose of a fuel system water separator on a turbine aircraft?
- To remove dissolved sulfur compounds that corrode turbine blades
- To remove free water from the fuel stream before it reaches the engine fuel control unit (Correct answer)
- To reduce fuel vapor pressure entering the fuel manifold
- To separate Jet-A from Jet-B if both are carried on the same aircraft
Correct answer: To remove free water from the fuel stream before it reaches the engine fuel control unit
A fuel/water separator removes free (undissolved) water from turbine fuel to prevent fuel control unit damage, ice formation in fuel nozzles, and combustion instability.
Question 3: When must the fuel cap be replaced on an aircraft with an integral (wet wing) fuel tank after servicing?
- Only after every third fueling to reduce wear on the threads
- Immediately after fueling; the tank must not be left uncapped for any reason during maintenance breaks (Correct answer)
- Only if a flight is departing within 30 minutes
- Only when the fuel quantity gauge is checked during preflight
Correct answer: Immediately after fueling; the tank must not be left uncapped for any reason during maintenance breaks
Fuel caps must be reinstalled and secured immediately after servicing to prevent fuel spillage, contamination, or vapor ignition, and the aircraft must not be left unattended with open fuel caps.
Question 4: What is the purpose of a fuel flow divider (distributor) on a fuel-injected reciprocating engine?
- To regulate total fuel flow to the engine based on throttle position
- To evenly distribute fuel to all individual fuel injector nozzles at equal pressure (Correct answer)
- To separate air from the fuel before it enters the cylinders
- To recirculate unused fuel back to the tanks
Correct answer: To evenly distribute fuel to all individual fuel injector nozzles at equal pressure
The flow divider (manifold valve or spider) distributes metered fuel equally among all fuel injection nozzles to ensure uniform fuel delivery to each cylinder.
Question 5: What is the significance of fuel quantity gauges being required to read accurately only at EMPTY in FAR Part 23 aircraft?
- This requirement means gauges must read zero only when the tank contains unusable fuel
- It means gauges are only required to be accurate at the empty indication; readings at other levels may be inaccurate, so preflight fuel verification by visual inspection or dipstick is essential (Correct answer)
- It means the empty reading triggers an automatic fuel pump switchover
- This requirement applies only to helicopter fuel gauges, not fixed-wing aircraft
Correct answer: It means gauges are only required to be accurate at the empty indication; readings at other levels may be inaccurate, so preflight fuel verification by visual inspection or dipstick is essential
FAR 23.1337 requires that fuel gauges read zero at the unusable fuel quantity level; the gauge need not be accurate at higher quantities, making physical verification critical.
Question 6: What is unusable fuel, and why is it listed in the aircraft weight and balance data?
- Fuel remaining after engine shutdown that drains back to the sump; it is listed because it affects gross weight
- Fuel that cannot be safely consumed in flight due to system design (e.g., below the fuel pickup tube); it is listed because it counts as aircraft empty weight (Correct answer)
- Fuel deliberately held in reserve for regulatory requirements only
- Fuel that has been contaminated and must be drained before flight
Correct answer: Fuel that cannot be safely consumed in flight due to system design (e.g., below the fuel pickup tube); it is listed because it counts as aircraft empty weight
Unusable fuel is the residual quantity trapped below the fuel pickup point that cannot feed the engine; it is part of the licensed empty weight and must be included in weight and balance calculations.
A&P Aircraft Fuel Systems 2
What is the hazard of misfueling a piston aircraft with Jet-A fuel instead of 100LL AVGAS?