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be disregarded or for various tactical purposes. As a general rule when OP DES or V/S modes are used, the descent is monitored using the Energy Circle, (displayed if HDG or TRK modes and
indicating the required distance to descend, decelerate and land from present position) and the level arrow on the ND. When the aircraft is not far away from the lateral F-PLN (small XTK), the yoyo on PFD is also a good indicator.
MANAGED DESCENT MODE
The managed descent profile from high altitude is approximately 2.5 °.
As an estimation of the distance to touchdown is required to enable descent profile monitoring, it is important to ensure that the MCDU F-PLN plan page reflects the expected approach routing. Any gross errors noted in the descent profile are usually a result of incorrect routing entered in the MCDU or non-sequencing of F-PLN waypoints, giving a false distance to touchdown.
DESCENT INITIATION
To initiate a managed descent, the pilot will set the ATC cleared altitude on the FCU and push the ALT selector. DES mode engages and is annunciated on the FMA. If an early descent were
required by ATC, DES mode would give 1 000 ft/min rate of descent, until regaining the computed profile.
NORMAL OPERATIONS
DESCENT
To avoid overshooting the computed descent path, it is preferable to push the FCU ALT selector
a few miles prior to the calculated TOD. This method will ensure a controlled entry into the descent and is particularly useful in situations of high cruise Mach number or strong tail winds.
If the descent is delayed, a "DECELERATE" message appears in white on the PFD and in amber on the MCDU. Speed should be reduced towards green dot, and when cleared for descent, the pilot will push for DES and push for managed speed. The speed reduction prior to 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.
NORMAL OPERATIONS
DESCENT
? 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.
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A330/A340 机组训练手册 FCTM Flight Crew Training Manual 1(59)
