What maintenance adjustments are typically allowed on an installed hydromechanical fuel control?

The correct answer pertains to the adjustments that can be made to the fuel control system, specifically adjustments related to fuel specific gravity. Fuel specific gravity is essential because it can affect how the hydromechanical fuel control calculates and manages fuel flow to the engine. Changes in fuel specific gravity can occur due to different types of fuel or environmental conditions, and the system may allow for calibration to maintain optimal engine performance under varying conditions.

The ability to adjust for fuel specific gravity helps ensure the correct fuel-to-air mixture, which is critical for engine efficiency and performance. It allows the fueling system to compensate for the density of the fuel being used, ensuring that the engine gets the proper amount of fuel it needs, especially in variations caused by fuel types or environmental factors.

In contrast, adjustments for fuel temperature, viscosity, and idle fuel pressure are typically managed by other factors or systems within the aircraft's engine management parameters and are not standard adjustments available in the hydromechanical fuel control itself.