Trouble Probable causes Remedy • No air to starter. • Propeller brake locked. • Starter speed low because of inadequate air  supply to starter. • If fuel is not observed leaving the exhaust pipe  during start, fuel selector valve may be  inoperative because of low power supply or  may be locked in “OFF.” • Fuel pump inoperative. • Aircraft fuel filter dirty. • Fuel control cutoff valve closed. • Insufficient fuel supply to control unit. • Fuel control main metering valve sticking. • Fuel control bypass valve sticking open. • Drain valve stuck open. Starting fuel  enrichment pressure switch setting too high. • Fuel control bypass valve sticking closed. • Fuel control acceleration cam incorrectly  adjusted.  • Defective fuel nozzle. • Fuel control thermostat failure. • Acceleration cam of fuel control incorrectly  adjusted. • Unstable fuel control governor operation. • Oil supply low. • Oil pressure transmitter or indicator giving false  indication. • Seal failure. • Faulty propeller governor. • Faulty fuel control or air sensing tip. • Vibration pickup or vibration meter malfunction. Power unit fails to turn over  during attempted start. Power unit fails to start. Engine fires, but will not  accelerate to correct speed. Acceleration temperature too  high during starting. Acceleration temperature  during starting too low. Engine speed cycles after  start. Power unit oil pressure drops  off severely. Oil leakage at accessory  drive seals. Engine unable to reach  maximum controlled speed of  100 percent. Vibration indication high. • Check started air valve solenoid and air supply. • Unlock brake by turning propeller by hand in  direction of normal rotation. • Check starter air valve solenoid and air supply. • Check power supply or electrically operated  valves. Replace valves if defective. • Check pump for sheared drives or internal  damage. Check for air leaks at outlet. • Clean filter and replace filtering elements if  necessary. • Check electrical circuit to ensure that actuator  is being energized. Replace actuator or control. • Check fuel system to ensure all valves are  open and pumps are operative. • Flush system. Replace control. • Flush system. Replace control. • Replace drain valve. Replace pressure switch. • Flush system. Replace control. • Replace control. • Replace nozzle with a known satisfactory unit.  • Replace control. • Replace control. • Continue engine operation to allow control to  condition itself. • Check oil supply and refill as necessary. • Check transmitter or indicator and repair or  replace if necessary. • Replace seal or seals. • Replace propeller control assembly. • Replace faulty control. If dirty, use air pressure  in reverse direction of normal flow through  internal engine passage and sensing tip. • Calibrate vibration meter.  • Start engine and increase power gradually.  • Observe vibration indicator. If indications prove  pickup to be at fault, replace it. If high vibration  remains as originally observed, remove power  unit for overhaul.  Figure 10-76.  Troubleshooting turboprop engines.  10-63