FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationMedium
A mechanic is studying the fuel control unit (FCU) on a turbine engine to understand how fuel flow is metered during operation. Which combination of inputs does the FCU primarily use to schedule fuel flow?
- AExhaust gas temperature and propeller pitch angle alone
- BBattery voltage and starter-generator load only
- CCabin pressure differential and outside air temperature
- DCompressor inlet temperature and pressure, engine speed, and power lever position
Show answer & explanationAnswer & explanation
Correct answer: D. Compressor inlet temperature and pressure, engine speed, and power lever position
A turbine engine's fuel control unit schedules fuel flow based on sensed compressor inlet air temperature and pressure, engine rotational speed (N1/N2), and pilot-commanded power lever position, ensuring proper fuel-air ratios and preventing compressor stalls or overtemperature during acceleration.
Why the other options are wrong
- A. EGT and propeller pitch are not primary FCU inputs (and turboprops use separate governing).
- B. Electrical parameters are unrelated to fuel scheduling logic.
- C. Cabin pressurization parameters have no bearing on engine fuel control.
Turbine Fuel Control Unit (FCU)
A hydromechanical or electronic device that schedules fuel flow to a turbine engine based on compressor inlet conditions, engine speed, and power lever position to maintain safe, efficient operation.
- Prevents compressor stall/surge during acceleration
- Prevents overtemperature by limiting fuel flow rate of increase
- May be hydromechanical, electronic (FADEC), or hybrid
Memory trick: FCU listens to speed, temp, pressure, and pilot's demand.