Figure 7-15.  Turbocharger components.  On most modern turbocharged engines, the position of  the waste gate is governed by a pressure-sensing control  mechanism coupled to an actuator. Engine oil directed into  or away from this actuator moves the waste gate position.  On these systems, the actuator is automatically positioned to  produce the desired MAP simply by changing the position  of the throttle control.  Other turbocharging system designs use a separate manual  control to position the waste gate. With manual control,  the manifold pressure gauge must be closely monitored to  determine when the desired MAP has been achieved. Manual  systems are often found on aircraft that have been modified  with aftermarket turbocharging systems. These systems  require special operating considerations. For example, if the  waste gate is left closed after descending from a high altitude,  it is possible to produce a manifold pressure that exceeds the  engine’s limitations. This condition, called an overboost,  may produce severe detonation because of the leaning effect  resulting from increased air density during descent.  Although an automatic waste gate system is less likely to  experience an overboost condition, it can still occur. If takeoff  power is applied while the engine oil temperature is below its  normal operating range, the cold oil may not flow out of the  As an aircraft equipped with a turbocharging system climbs,  the waste gate is gradually closed to maintain the maximum  allowable manifold pressure. At some point, the waste gate  is fully closed and further increases in altitude cause the  manifold pressure to decrease. This is the critical altitude,  A pilot flying an aircraft with a turbocharger should be aware  of system limitations. For example, a turbocharger turbine  and impeller can operate at rotational speeds in excess of  80,000 rpm while at extremely high temperatures. To achieve  high rotational speed, the bearings within the system must be  constantly supplied with engine oil to reduce the frictional  forces and high temperature. To obtain adequate lubrication,  the oil temperature should be in the normal operating range  before high throttle settings are applied. In addition, allow  the turbocharger to cool and the turbine to slow down before  shutting the engine down. Otherwise, the oil remaining in  the bearing housing will boil, causing hard carbon deposits  to form on the bearings and shaft. These deposits rapidly  deteriorate the turbocharger’s efficiency and service life. For  further limitations, refer to the AFM/POH.  waste gate actuator quickly enough to prevent an overboost.  To help prevent overboosting, advance the throttle cautiously  to prevent exceeding the maximum manifold pressure limits.  7-14  High Altitude Performance  System Operation  Exhaust gas discharge  Pressurized air from the  turbocharger is supplied  to the cylinders.  Intake manifold  Intake air is ducted to the  turbocharger where it is  compressed.  Air intake This controls the amount  of exhaust through the  turbine. Waste gate  position is actuated by  engine oil pressure.  Waste gas  The turbocharger in­ corporates a turbine,  which is driven by ex­ haust gases and a com­ pressor that pressurizes  the incoming air.  Turbocharger  This regulates airflow  to the engine.  Throttle body  Exhaust gas is ducted  through the exhaust man­ ifold and is used to turn  the turbine which drives  the compressor.  Exhaust manifold 