TM 55-1520-240-23-7
8-1
ENGINE INSTRUMENTS
8-1
POWER TURBINE INLET TEMPERATURE (PTIT)
AND EMERGENCY POWER INDICATING SYSTEM
WITHOUT 74
Description
Except for component locations, the PTIT and
emergency power indicating circuits are identical for
each engine. The PTIT system uses a 10-probe
thermocouple to measure temperature at the inlet to
the engine power turbine section. This temperature is
displayed on indicators, one for each engine, on the
center instrument panel. The emergency power and
indicating system includes a set-point circuit in each
indicator, an EMERG PWR light for each engine, and an
emergency power panel. The set-point circuit is factory
adjusted to provide a signal when PTIT is 890º to 910ºC.
This indicates the engine is providing emergency power.
When an engine is operated at emergency power, the
EMERG PWR light comes on.
NO BREAK - WORK HARDER
The EMERG PWR lights are located on the pilot’s
and copilot’s instrument panels. When PTIT exceeds
910ºC for at least 4 seconds, a timer starts recording
overtemperature duration. A striped latch display on
the emergency power panel indicates that the engine
was operated under emergency power and alerts
maintenance personnel to record time and perform any
necessary inspections or maintenance. The emergency
power panel is located in the cockpit overhead panel,
below the engine condition panel.
NO BREAK - WORK HARDER
Thermocouple probes (10) are in tubes around the
power turbine nozzle. The probes extend into the gas
stream between the vanes of the third turbine nozzle.
Heat from the combustion chamber causes the probes
to generate a voltage proportional to the heat. This
voltage is applied to the No. 1 PTIT indicator and the
indicator displays the temperature on a scale calibrated
0 to 1,200ºC.
8-2
