Trouble Probable Cause Remedy Aircraft fails to  reach critical  altitude Engine surges Wastegate will  not close fully Wastegate will  not open Differential  controller malfunctions Density controller malfunctions Damaged compressor or turbine wheel Exhaust system leaks Faulty turbocharger bearings Wastegate will not close fully Malfunctioning controller Bootstrapping Wastegate malfunction Controller malfunction Wastegate bypass valve bearing tight Oil inlet orifice blocked Differential controller malfunction Broken wastegate linkage Oil outlet obstructed Broken wastegate linkage Controller malfunction Seals leaking Diaphragm broken Controller valve stuck Seals leaking Bellows damaged Valve stuck Replace turbocharger Repair leaks Replace turbocharge Refer to wastegate in the trouble column Refer to differential controller in the trouble column Ensure engine is operated in proper range Refer to wastegate in the trouble column Refer to differential controller in the trouble column Replace bypass valve Clean orifice Refer to controller in the trouble column Replace linkage and adjust waste gate for proper opening and closing Clean and reconnect oil return line Replace linkage and adjust waste gate opening and closing Refer to controller in the trouble column Replace controller Replace controller Replace controller Replace controller Replace controller Replace controller Figure 3-23.  Common issues when troubleshooting turbocharger systems. Figure 3-24.  An example of a turbine engine inlet. the engine. The inlet varies according to the type of turbine  engine. Small turboprop and turboshaft engines have a  lower airflow than large turbofan engines which require a  completely different type of inlet. Many turboprop, auxiliary power units, and turboshaft engines use screens that cover  the inlet to prevent foreign object damage (FOD).  As aircraft speed increases, thrust tends to decrease  somewhat; as the aircraft speed reaches a certain point, ram  recovery compensates for the losses caused by the increases  in speed. The inlet must be able to recover as much of the total  pressure of the free airstream as possible. As air molecules  are trapped and begin to be compressed in the inlet, much  of the pressure loss is recovered. This added pressure at the  inlet of the engine increases the pressure and airflow to the  engine. This is known as “ram recovery” or “total pressure  recovery.” The inlet duct must uniformly deliver air to  the compressor inlet with as little turbulence and pressure  variation as possible. The engine inlet duct must also hold  the drag effect on the aircraft to a minimum. Air pressure drop in the engine inlet is caused by the friction  of the air along both sides of the duct and by the bends in the  duct system. Smooth flow depends upon keeping the amount  of turbulence to a minimum as the air enters the duct. On  engines with low flow rates, turning the airflow allows the  engine nacelle to be smaller and have less drag. On turbofan  engines, the duct must have a sufficiently straight section to  ensure smooth, even airflow because of the high airflows.  3-18