FAA Commercial Pilot Airplane (CAX)Aircraft SystemsHard
In a fuel injection system, the fuel control unit (metering unit) primarily determines fuel flow to the engine cylinders based on:
- Apropeller RPM and oil pressure
- Bcabin altitude and turbocharger wastegate position
- Cairflow through the intake system (reflected by throttle position/engine speed) and the mixture control setting
- Dmixture control setting and manifold pressure alone, independent of airflow
Show answer & explanationAnswer & explanation
Correct answer: C. airflow through the intake system (reflected by throttle position/engine speed) and the mixture control setting
The fuel control unit meters fuel proportional to engine airflow demand (sensed via throttle position and engine speed) and adjusts fuel flow further according to the pilot's mixture control setting, maintaining the correct fuel-to-air ratio across power settings and altitudes.
Why the other options are wrong
- A. Propeller RPM and oil pressure are unrelated to fuel metering in the injection system.
- B. Cabin altitude and wastegate position relate to pressurization/turbocharging, not fuel metering.
- D. Metering must consider airflow, not manifold pressure alone.
Fuel Control Unit (Metering Unit)
A fuel injection component that meters fuel flow based on engine airflow demand and the pilot's mixture setting to maintain the correct fuel-air ratio.
- Airflow is sensed via throttle position/engine speed
- Mixture control allows leaning at altitude
- Provides more precise fuel metering than a carburetor
Memory trick: Airflow tells how much, mixture tells how rich.