A turbine fuel control system that has no electronic interface is classified as which type?

• A. Electrohydromechanical
• B. Digital electronic
• C. Hydromechanical
• D. Pneumatic-hydraulic

Answer: (C)

The key idea is how the control relies on mechanical and hydraulic action rather than electronics. A turbine fuel control with no electronic interface operates purely through hydraulic pressure and mechanical linkages to metering the fuel. In a hydromechanical setup, a hydraulic servo and mechanical governor work together—springs, cams, and linkages respond to engine conditions (like speed and demand) and position the fuel metering valve accordingly, all without any electronic sensors, controllers, or actuators.

If electronics were involved, you’d be dealing with electrohydromechanical or digital electronic controls, where electronic interfaces alter the hydraulic signal or directly drive the valve. A pneumatic-hydraulic arrangement would incorporate air-driven elements as part of the actuation, which is a different modality than a purely hydraulic-mechanical system. Hence, the best fit for a system lacking an electronic interface is hydromechanical.