Which of the following is NOT an HMU input affecting fuel flow to the combustor?

Which of the following is NOT an HMU input affecting fuel flow to the combustor?

• A. Boost pump discharge pressure
• B. Collective through the LDS
• C. PCL through the PAS
• D. DEC through the torque motor

Answer: (C)

Fuel flow to the combustor is controlled by the HMU through signals that tell it how much fuel to meter based on demand and current engine state. The boost pump discharge pressure provides the fuel supply pressure the HMU uses to meter fuel. The collective position, transmitted through the LDS, represents the pilot’s demand for more thrust and feeds the HMU so it increases fuel flow accordingly. The torque motor, driven by the DEC signal, directly positions the metering valve inside the HMU to adjust fuel flow to meet the engine’s torque demand. The PCL signal, when routed through the PAS, does not feed the HMU’s metering valve as a direct input to fuel flow. Its influence on engine power is managed through the PAS pathway rather than as a direct HMU input to the combustor, so it’s not a direct HMU input affecting fuel flow.

Fuel flow to the combustor is controlled by the HMU through signals that tell it how much fuel to meter based on demand and current engine state. The boost pump discharge pressure provides the fuel supply pressure the HMU uses to meter fuel. The collective position, transmitted through the LDS, represents the pilot’s demand for more thrust and feeds the HMU so it increases fuel flow accordingly. The torque motor, driven by the DEC signal, directly positions the metering valve inside the HMU to adjust fuel flow to meet the engine’s torque demand.

The PCL signal, when routed through the PAS, does not feed the HMU’s metering valve as a direct input to fuel flow. Its influence on engine power is managed through the PAS pathway rather than as a direct HMU input to the combustor, so it’s not a direct HMU input affecting fuel flow.