I A P 2 0 2 3 . 0 0 1 - A F M / I R I S T E X A N I I P A G E | 30
FOR SIMULATION USE ONLY – NOT A TRAINING AID
raises N1 to maintain NP above 80% to avoid the stress on the propeller during
spins.
Power setting is linear with PCL position throughout the operating envelope of the
aircraft; for example, if the max power available at a given condition is 1000 SHP,
the engine will schedule 1000 SHP at max PCL, and 500 SHP at 50% of the way
between max and idle.
The PMU controls acceleration and deceleration allowing PCL movement as rapidly
as desired at any altitude, minimizes propeller effects, and avoids large thrust
surges on engine acceleration as the propeller stabilizes at operating RPM.
The PMU provides an auto-start capability during ground starts, monitoring engine
parameters as the start progresses. The auto-start feature will automatically
terminate the ground start sequence if light-off has not occurred within 10 seconds
of selecting AUTO/RESET with the STARTER switch (no start) or if the PMU projects
an impending hung or hot start.
The PMU will abort an auto start attempt to avoid a hung or hot start if ITT exceeds
940 °C for 2 seconds, 870 °C for 4 seconds, or 840 °C for 19 seconds.
An auto abort will also occur if N1 acceleration rate to idle is less than 50% of
normal.
The engine start sequencing (starter, igniters, and fuel controlled during the start
and shut off after a successful start) is available for air-starts, but the automatic
shutdown feature is disabled when in flight mode.
For engine starts, the PMU receives inputs from the aircraft IOAT sensor located in
the engine inlet plenum. During high temperature operations, radiant heat from the
engine may heat soak the IOAT sensor, raising IOAT beyond ambient temperatures.
When this occurs and IOAT is greater than 96 °C but less than 121 °C, the PMU
defaults to 121 °C for all PMU functions (including IOAT display).
If IOAT does not exceed 96 °C, the PMU uses the displayed value. If the PMU is
activated with IOAT at/or above 96 °C, IOAT and ITT data is invalid (red X’S in counter
display and missing ITT pointer) and EDM FAIL warning is displayed on the EICAS
display.
If IOAT exceeds 121 °C, the PMU goes offline. This condition is indicated by red X’s in
the IOAT and ITT counters, removal of the ITT pointer on the EICAS display, and by
illumination of the PMU FAIL warning on the EICAS.
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