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temperature datum operates electrically and has limited authority to schedule fuel to maintain
target turbine inlet temperatures. When active (TD switches in the AUTO position), the
temperature datum system operates in one of three modes:
Start Limiting
Temperature Limiting
Temperature Controlling
Engine RPM < 94%
Engine RPM > 94% and
throttle
less
than 65º throttle
lever angle
Engine RPM > 94% and
throttle
more
than 65º throttle
lever angle
Reduces fuel flow when TIT
reaches 820 º C to protect 830º
C
Reduces fuel flow to protect
1083 º C (Takeoff TIT limit).
TD correction lights
illuminated.
Schedules TIT as a function of
throttle position. Reduces fuel
flow to protect 1083 º C
(Takeoff TIT limit). TD
correction lights extinguished.
As the throttles are advanced in the flight range, there is a distinctive "torque bump" when the
TD system kicks into the temperature controlling range at 65 degrees of throttle lever angle. In
the temperature controlling range, the TD system schedules TIT with throttle position. If it is
necessary to trim the aircraft at conditions where the throttles are near the torque bump, the TD
valves may be locked. The engines should not be operated at altitudes or temperatures far from
where the TD valves were locked.