What is the correct order to reduce power output for an engine with a constant-speed propeller?

To properly reduce power output in an engine equipped with a constant-speed propeller, the correct sequence is to first reduce the manifold pressure and then adjust the RPM.

When you reduce the manifold pressure, you are decreasing the amount of air-fuel mixture available for combustion. This decrease in power demand allows the engine to operate at a lower output while maintaining a suitable level of operation. Following this, you adjust the RPM to match the desired power level that corresponds with the new manifold pressure. This step is crucial because the constant-speed propeller's goal is to maintain optimal engine performance and efficiency, and adjusting these parameters in that order helps maintain smooth engine operation.

The particular sequence emphasizes managing the engine performance without risking engine stress or inefficient operation. Starting with manifold pressure ensures you're adjusting the power output before handling the engine speed, which could lead to an undesired increase in RPM or potential overspeed conditions if not managed properly.