PMU 1-24 Flashcards
What powers the PMU?
The 32 VAC permanent magnet alternator (PMA)
The PMU automatically switches to the ________ bus when propeller
RPM drops below __________ or when ______.
28 VDC battery; 40-50% NP; the PMU fails
The PMU operates in either _____or ______mode
flight; ground
Where is the aircraft weight-on-wheels switches located?
on the main gear struts
In ground mode, idle is _________, and in flight mode, idle is _______.
60-61% N1; 67% N1 (min).
Above _________, the
PMU raises N1 to maintain NP above _____ to avoid the stress on the propeller during spins
10,000 feet PA; 80%
The autostart feature will automatically terminate the ground start sequence if light-off has not occurred within _______ of selecting AUTO/RESET with the STARTER switch (no
start) or if the PMU projects an impending hung or hot start.
10 seconds
The PMU will abort an auto start attempt to avoid a hung or hot start in what three cases?
if ITT exceeds:
940 °C for 2 seconds,
870 °C for 4 seconds,
840 °C for 19 seconds
An auto abort will occur if N1 acceleration rate to idle is less than _______
50% of normal
If IOAT is greater than ______ but less than ______ , the PMU will default to ______ for all PMU functions (including IOAT display).
96°C; 121 °C; 121 °C
If IOAT does not exceed ______, the PMU will use the displayed value
96 °C
If IOAT exceeds 121 °C, the PMU will do what?
go offline
The PMU will reset with IOAT above 121°C.
False.
Following the illumination of the ST READY annunciator,
it will remain illuminated for _________, even if the PCL is
moved out of the auto start position.
3 seconds
To prevent initiation of
an engine start without auto start protection, ensure the _______ annunciator remains illuminated for more than _______ prior to selecting AUTO/RESET
ST READY; 3 seconds
During a start the PMU activates what?
the starter, boost pump, and igniters, and adds fuel at the proper N1
At approximately________, the starter and igniters are deenergized and the boost pump is deactivated if fuel pressure is above _______.
50% N1; 10 PSI
The PCL may be advanced to IDLE any time N1
is ______
at or above 60%
If the ST READY annunciator
extinguishes for any reason during the start sequence, the
PMU will still provide automatic protection
False. It will not
If the PCL has been advanced
past the auto start position, the PMU will not cut off fuel to
terminate a start.
True
How do you abort a start if the PCL is moved out of ST READY position?
Manually by moving the PCL back to OFF, or if the PCL has not been moved past the IDLE gate, by reselecting the STARTER switch to AUTO/RESET.
How to terminate a start if the PCL has been moved past the
IDLE gate?
the PCL must be moved to OFF to abort the start.
The PMU also provides engine protection during an airstart.
False.
During an airstart, automatic N1, ITT, and torque limit protection is unavailable, therefore, the pilot must monitor all parameters and abort the start manually if necessary.
How to identify that the PMU is in manual mode?
Illumination of both the PMU FAIL and PMU STATUS annunciators indicates the system is in manual
mode.
In PMU manual mode the maximum increase in power is ________, and the maximum decrease in power is ______.
280 shp, 550 shp
With the PMU in manual mode there will be a step change in NP.
False. No step change in NP will occur since the overspeed governor is automatically reset to 100%
In manual mode, the PCL schedules fuel directly to
the engine through the FMU and the pilot must exercise care to ensure N1, temperature, and torque limits are not
exceeded.
True
The PMU STATUS light will illuminate 1 minute after landing if?
if fault conditions that are
not serious enough to revert the system to manual are
encountered in flight
What does PMU STATUS in flight indicate?
PMU STATUS light illumination in flight indicates a fault in either of, or a mismatch between the
weight-on-wheels switches, and serves to notify the pilot
that the PMU will not revert to ground mode upon landing.
With PMU STATUS in flight idle N1 will still shift from flight idle to ground idle upon landing,
False.
