This article will cover things that cause problems with propeller governor systems and how to diagnose them. Often, governor problems don't give any warning until something obvious happens, such as the inability to hold selected RPM, the propeller surges or seeks an RPM, or is airspeed-sensitive. In the case of twins, the problem may manifest itself as the propeller occasionally or often going into uncommanded feather, especially on landing rollout.There are a number of different components in the system that can cause these symptoms. Let's look at the different causes and troubleshooting procedures, starting with the most common complaint, that being the lack of major RPM control.In single-engine aircraft, this shows up as the RPM being too high, and the apparent inability of the governor to keep the RPM down. In twin-engine aircraft this shows up as the opposite, with RPM too low, and the governor's apparent inability to bring the RPM up to the set speed.There are a few things that cause this symptom: 1) Sticky prop -- sticking blades or actuating piston, or hydraulic lock; 2) Bad leak at the case-to-crank transfer point; and 3) Leaking pilot valve in the governor or low-governor oil pressure.
This is a companion discussion topic for the original entry at https://www.avweb.com/ownership/propeller-governor-diagnostics