AOA data is used by the Fast/Slow (F/S) pointer (Primus APEX Build 7 or lower) or by the Dynamic Speed Bug
(DSB) (Primus APEX Build 8 and higher) on the left of the Primary Flight Display (PFD). The data is also used to
show the Low Speed Awareness Indication adjacent to the Air Speed tape on the PFD.
The stick pusher computer processes the aircraft angle of attack, flap position, weight on wheel and engine
condition signals. When the aircraft is near the stall angle, the stick pusher computer operates the stick shaker
actuator to warn the pilot of the situation. If no manual correction is made the stick pusher computer operates the
stick pusher servo when the aircraft gets nearer the stall angle, to automatically correct the aircraft attitude.
The stick pusher computer also changes the stall angle datums between normal mode operation and ice mode
operation when the pusher ice mode relay energizes.
2.3
Stick Pusher Servo/Capstan
The stick pusher servo operates the elevator cable system to make the aircraft pitch go nose-down. It is installed
below the floor between frames 21 and 22. The stick pusher servo is in a rectangular box that has a splined drive
shaft at the front and an electrical connector on the rear.
Inside the stick pusher servo there is an accelerometer circuit with a g-switch. The g-switch operates when the
vertical acceleration due to gravity (g) is less than 0.5 g. This gives an inhibit signal to stop the operation of the
stick pusher servo.
The output torque of the stick pusher servo is electronically limited to give a control force of 24,9 to 31,8 kgf (55 to
70 lbf). The stick pusher servo monitors its electronic circuits and, if there is a fault, sends a signal to the MAU that
makes the amber PUSHER caution message come on.
The stick pusher servo is installed on a capstan mount which has a base, a capstan and a mechanical slip clutch.
The clutch operates at a control force of 31,8 to 40,8 kgf (70 to 90 lbf ). A cable installed on the capstan connects
to the elevator control cable. The slip clutch lets the pilot override the stick pusher servo if incorrect operation
occurs. The slip clutch operates if the torque given to the capstan from the elevator control cable is more than the
slip clutch limit.
The stick pusher servo is controlled by the two independent channels of the stick pusher computer. If both channels
send a push command, the electrical clutch is engaged and the servo is activated. This results in a nose down
movement on the pitch controls. If only the left hand stick pusher computer sends a push command, it has no effect
on the system. If only the right hand stick pusher computer sends a push command, the electrical clutch of the
push servo engages and makes the movement of the control column heavy.
In case the stick pusher servo detects a discrepancy in the commands between the left hand and right hand stick
pusher computer, a PUSHER caution is indicated after 3.5 seconds.
2.4
Stick Shaker Actuator
The stick shaker actuator vibrates the pilot and co-pilot control columns to give a warning that the aircraft is near
the stall speed. The stick shaker actuator is attached to a tube of the left control column behind the instrument
panel. It is a motor with a reduction gear and an off-center weighted disc in a housing. On the rear of the housing is
an electrical connector.
2.5
PUSHER INTR Switch
PUSHER INTR switches are installed on the pilot and co-pilot control wheels. The PUSHER INTR switches are
used to stop the operation of the stick pusher servo if incorrect operation occurs.
The PUSHER INTR switch installed on the pilot’s control wheel stops the operation of the stick pusher servo. The
electrical clutch disengages and lets the control column move freely.
PC-12/47E AMM Doc No 02300, ISSUE 01 REVISION 26 MSN 545, 1001-1719,
1721-1999
12-B-AM-00-00-00-I
UNCLASSIFIED
Effectivity: All
12-B-22-20-00-00A-040A-A
UNCLASSIFIED
2021-12-04 Page 4
