Pilot's Operating Handbook
Section 7
Description
Edition 0 - March 05, 2019
Rev. 2
Page 7.7.8
- Altitude 3 000 ft, Selected Cruise Schedule : Maximum Cruise. Speed
Constr
aint = 120 kt.
- AT mode : SPD 120 KT
- Managed AT TRQ ≃ 30 % (torque corresponding to target airspeed)
- IAS = 120 kt
Descent
For descent with the AT engaged, it is recommended to use the FLC or VS FD
vertical mode.
When FLC is active, AT engagement activates the DESC AT mode that sets and
maintains engine power to approximately 10 % TRQ. Then, the target airspeed is
tracked via FD pitch orders. In MAN mode, the target airspeed is the manually
selected airspeed. In FMS mode, the target airspeed is retrieved from the FMS
descent schedule.
When
VS is active, AT engagement activates the SPD XXXKT AT mode that
controls engine power within operational limits to reach and maintain the target
airspeed. In MAN mode, the target airspeed is the manually selected airspeed. In FMS
mode, the target airspeed is retrieved from the FMS descent schedule. Then, the
target vertical speed is tracked via FD pitch orders.
Approach
For approaches (i.e. from the Initial Approach Fix), the SPD source switch must be in
MAN mode or the autothrottle must be disengaged - refer to section 2.6.2 Autothrottle
limits.
This is because use of AT in FMS mode until final approach may result in an
unstabilized approach, because the predefined FMS descent schedule is not
appropriate for approach. A go-around maneuver may be necessary, due to all of the
following :
- Airspeed may be too high at GS/GP capture
- Airspeed may be too high to timely configure the aircraft before landing
- AT automatically disengages at GS/GP capture and cannot be re-engaged, ifin
FMS mode.
As a result, only MAN mode is permitted for approach, to ensure an appropriate
airspeed management until touchdown.
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