When the CSU changes power, the change is shown on MAP or RPM?

• A. MAP
• B. RPM
• C. Fuel flow
• D. Oil temperature

Answer: (A)

When the CSU changes power, the indication that best reflects that change is the pressure inside the intake manifold. The CSU adjusts fuel flow to increase or decrease engine output, and as more or less air is drawn into the cylinders, the manifold pressure rises or falls accordingly. This manifold absolute pressure (MAP) is a direct, real-time measure of the engine’s power setting. RPM, while related to how hard the engine is working, is often controlled or limited by a propeller governor or by the load on the engine, so it doesn’t rise and fall in as direct a way as MAP when the CSU makes a power change. Fuel flow and oil temperature change with power too, but they don’t provide as immediate or as direct a readout of the power change as MAP does.