AMP - Aviation Maintenance Technician Powerplant Practice Exam

How does the propeller overspeed governor on a turboprop engine decrease propeller rpm?

1. When oil pressure is decreased, the return spring and counterweights force the oil out of the servo piston

2. As oil pressure increases, the servo piston is pushed forward, and the feather spring is compressed

3. When oil pressure is increased, the return spring and counterweights force the oil out of the servo piston

4. By opening a bypass valve that allows more oil to flow into the feathering system

The correct answer is: When oil pressure is decreased, the return spring and counterweights force the oil out of the servo piston

The other options are incorrect because they do not accurately describe how the propeller overspeed governor decreases propeller rpm. Option A is correct because when oil pressure is decreased, the return spring and counterweights force the oil out of the servo piston, which in turn causes the propeller pitch to increase, decreasing propeller rpm. Option B is incorrect because increasing oil pressure would cause the servo piston to move forward, compressing the feather spring and increasing propeller pitch, leading to an increase in propeller rpm instead of a decrease. Option C is incorrect because increasing oil pressure would cause the oil to be forced out of the servo piston, increasing propeller pitch and propeller rpm. Option D is incorrect because opening a bypass valve would allow more oil to flow into the feathering system, which would decrease propeller pitch and actually increase propeller rpm. Therefore, option A is the correct answer as it accurately describes the process by which the propeller overspeed governor decreases propeller rpm.