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descent will enable the aircraft to recover the computed profile more quickly as it accelerates to
the managed descent speed.
DESCENT PROFILE
When DES with managed speed is engaged, the AP/FD guides the aircraft along the
pre-computed descent path determined by a number of factors such as altitude constraints,
wind and descent speed. However, as the actual conditions may differ from those planned, the
DES mode operates within a 20 kt speed range around the managed target speed to maintain
the descent path.
Managed descent: speed target range principle
If the aircraft gets high on the computed descent path:
• The speed will increase towards the upper limit of the speed range, to keep the aircraft on
the path with IDLE thrust.
• If the speed reaches the upper limit, THR IDLE is maintained, but the autopilot does not
allow the speed to increase any more, thus the VDEV will slowly increase.
A330/A340 FLIGHT CREW TRAINING MANUAL
NORMAL OPERATIONS
DESCENT
A330/A340 FLEET NO-080 P 4/8
FCTM 17 JUN 09
• A path intercept point, which assumes half speedbrake extension, will be displayed on
the ND descent track.
• If speed brakes are not extended, the intercept point will move forward. If it gets close to
a an altitude constrained waypoint, then a message "EXTEND SPEEDBRAKES" will be
displayed on the PFD and MCDU.
This technique allows an altitude constraint to be matched with minimum use of
speedbrakes.
When regaining the descent profile, the speedbrakes should be retracted to prevent the
A/THR applying thrust against speedbrakes. If the speedbrakes are not retracted, the "SPD
BRK" message on the ECAM memo becomes amber and "RETRACT SPEEDBRAKES" is
displayed in white on the PFD.
A/C above descent path
If the aircraft gets low on the computed descent path
The speed will decrease towards the lower limit of the speed range with idle thrust. When
the lower speed limit is reached the A/THR will revert to SPEED/MACH mode and apply
thrust to maintain the descent path at this lower speed. The path intercept point will be
displayed on the ND, to indicate where the descent profile will be regained.
A/C below descent path
A330/A340 FLIGHT CREW TRAINING MANUAL
NORMAL OPERATIONS
DESCENT
A330/A340 FLEET NO-080 P 5/8
FCTM 17 JUN 09
If selected speed is used:
The descent profile remains unchanged. As the selected speed may differ from the speed
taken into account for pre-computed descent profile and speed deviation range does not
apply, the aircraft may deviate from the descent profile e.g. if the pilot selects 275 kt with a
pre-computed descent profile assuming managed speed 300 kt, VDEV will increase.
SELECTED DESCENT MODE
There are 2 modes for flying a selected descent, namely OP DES and V/S. These modes will be
used for pilot tactical interventions.
V/S mode is automatically selected when HDG or TRK mode is selected by the pilot, while in DES
mode. Furthermore, in HDG or TRK mode, only V/S or OP DES modes are available for descent.
To initiate a selected descent, the pilot should set the ATC cleared altitude on the FCU and pull
the ALT selector. OP DES mode engages and is annunciated on the FMA. In OP DES mode, the
A/THR commands THR IDLE and the speed is controlled by the THS.
Speed may be either managed or selected. In managed speed, the descent speed is displayed
only as a magenta target but there is no longer a speed target range since the pre-computed flight
profile does not apply.
The AP/FD will not consider any MCDU descent altitude constraints and will fly an unrestricted
descent down to the FCU selected altitude.
If the crew wishes to steep the descent down, OP DES mode can be used, selecting a higher
speed. Speedbrake is very effective in increasing descent rate but should be used with caution at
high altitude due to the associated increase in VLS.
If the pilot wishes to shallow the descent path, V/S can be used. A/THR reverts to SPEED mode.
In this configuration, the use of speedbrakes is not recommended to reduce speed, since this
would lead to thrust increase and the speed would be maintained.
MODE REVERSION
Applicable to: ALL
If a high V/S target is selected (or typically after a DES to V/S reversion), the autopilot will pitch the
aircraft down to fly the target V/S. Thus the aircraft will tend to accelerate, while A/THR commands
idle thrust to try to keep the speed. When IAS will reach a speed close to VMO or VFE, the autopilot
will pitch the aircraft up, so as to fly a V/S allowing VMO or VFE to be maintained with idle thrust.
Triple click will be triggered.
A330/A340 FLIGHT CREW TRAINING MANUAL
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A330/A340机组训练手册FLIGHT CREW TRAINING MANUAL(47)
