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the air is less dense and therefore, cools less
efficiently. Also, the less dense air causes the
compressor to work harder. Compressor turbine
speeds can reach 80,000 – 100,000 r.p.m., adding
to the overall engine operating temperatures.
Turbocharged engines are also operated at higher
power settings a greater portion of the time.
High heat is detrimental to piston engine operation. Its
cumulative effects can lead to piston, ring, and
cylinder head failure, and place thermal stress on other
operating components. Excessive cylinder head
temperature can lead to detonation, which in turn can
cause catastrophic engine failure. Turbocharged
engines are especially heat sensitive. The key to
turbocharger operation, therefore, is effective heat
management.
The pilot monitors the condition of a turbocharged
engine with manifold pressure gauge, tachometer,
exhaust gas temperature/turbine inlet temperature
gauge, and cylinder head temperature. The pilot
manages the “heat system” with the throttle, propeller
r.p.m., mixture, and cowl flaps. At any given cruise
power, the mixture is the most influential control over
the exhaust gas/turbine inlet temperature. The throttle
regulates total fuel flow, but the mixture governs the
fuel to air ratio. The mixture, therefore, controls
temperature.
Exceeding temperature limits in an after takeoff climb
is usually not a problem since a full rich mixture cools
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with excess fuel. At cruise, however, the pilot normally
reduces power to 75 percent or less and simultaneously
adjusts the mixture. Under cruise conditions,
temperature limits should be monitored most closely
because it’s there that the temperatures are most likely
to reach the maximum, even though the engine is
producing less power. Overheating in an enroute
climb, however, may require fully open cowl flaps and
a higher airspeed.
Since turbocharged engines operate hotter at altitude
than do normally aspirated engines, they are more
prone to damage from cooling stress. Gradual
reductions in power, and careful monitoring of
temperatures are essential in the descent phase. The
pilot may find it helpful to lower the landing gear to
give the engine something to work against while power
is reduced and provide time for a slow cool down. It
may also be necessary to lean the mixture slightly to
eliminate roughness at the lower power settings.
TURBOCHARGER FAILURE
Because of the high temperatures and pressures
produced in the turbine exhaust systems, any
malfunction of the turbocharger must be treated with
extreme caution. In all cases of turbocharger operation,
the manufacturer’s recommended procedures should
be followed. This is especially so in the case of
turbocharger malfunction. However, in those instances
where the manufacturer’s procedures do not
adequately describe the actions to be taken in the event
of a turbocharger failure, the following procedures
should be used.
OVERBOOST CONDITION
If an excessive rise in manifold pressure occurs during
normal advancement of the throttle (possibly owing to
faulty operation of the waste gate):
• Immediately retard the throttle smoothly to limit
the manifold pressure below the maximum for
the r.p.m. and mixture setting.
• Operate the engine in such a manner as to avoid a
further overboost condition.
LOW MANIFOLD PRESSURE
Although this condition may be caused by a minor
fault, it is quite possible that a serious exhaust leak has
occurred creating a potentially hazardous situation:
• Shut down the engine in accordance with the
recommended engine failure procedures, unless
a greater emergency exists that warrants continued
engine operation.
• If continuing to operate the engine, use the lowest
power setting demanded by the situation and
land as soon as practicable.
It is very important to ensure that corrective
maintenance is undertaken following any
turbocharger malfunction.
RETRACTABLE LANDING GEAR
The primary benefits of being able to retract the
landing gear are increased climb performance and
higher cruise airspeeds due to the resulting decrease in
drag. Retractable landing gear systems may be
operated either hydraulically or electrically, or may
employ a combination of the two systems. Warning
indicators are provided in the cockpit to show the pilot
when the wheels are down and locked and when they
are up and locked or if they are in intermediate
positions. Systems for emergency operation are also
　
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