Some brief examples of troubleshooting problems and possible causes are provided in the following subsections. Always refer to the correct manual for actual information on troubleshooting.
Hunting and Surging
Hunting is characterized by a cyclic variation in engine speed above and below desired speed. Surging is characterized by a large increase/decrease in engine speed, followed by a return to set speed after one or two occurrences. If propeller is hunting, an appropriately licensed repair facility should check:
- Fuel control, and
- Synchrophaser or synchronizer.
Engine Speed Varies With Flight Attitude (Airspeed)
Small variances in engine speed are normal and are no cause for concern. An increase in engine speed while descending or increasing airspeed with a nonfeathering propeller could be.
- The governor not increasing oil volume in the propeller.
- Engine transfer bearing leaking excessively.
- Excessive friction in blade bearings or pitch changing mechanism.
Failure to Feather or Feathers Slowly
Failure to feather or slow feathering of the propeller requires the FAA-certificated A&P technician to:
- Refer to the air charge section in the maintenance manual if the air charge is lost or low.
- Check for proper function and rigging of propeller/ governor control linkage.
- Check the governor drain function.
- Check the propeller for misadjustment or internal corrosion (usually in blade bearings or pitch change mechanism) that results in excessive friction. This must be performed at an appropriately licensed propeller repair facility.