(b)
Climb (CLB) Predictions in climb start by an acceleration segment from V2 +10 kts until the lowest speed between:
-
the optimum or the selected climb speed,
-
the speed limit,
-any climb speed constraint, if reached.
The speed profile satisfies therefore all the speed constraints
and limits until the last waypoint or altitude constraint is
satisfied. The altitude profile, based on this speed profile and
max climb thrust is limited by any AT or BELOW altitude
constraint (if any). The speed profile is not modified to satisfy
high altitude constraint. The constraints in climb are outlined
by a star "*" on the corresponding field in the F.PLN page.
The star is normally magenta but can be amber if the system
predicts that the constraint will be missed.
The end of the climb phase is indicated by the pseudo waypoint
T/C on the F.PLN page.
(c)
Cruise (CRZ) For cruise, predictions compute speed, time and fuel assuming altitude hold at the cruise flight level. One or more (up to 4) step climb or descent may exist. The speed profile in optimum mode (ECON) varies as the weight decreases during the flight. The T/D pseudo waypoint which terminates the cruise phase is computed by the descent profile calculation. From takeoff to cruise phase, the predictions and the profile are recomputed periodically or following modification of any flight plan elements or speed or weight.
(d)
Descent (DES) In order to get predictions for the descent phase, a descent path is computed backwards from the first approach point to the cruise flight level. This path is divided into two parts. The bottom part is a geometric path defined by straight segments in space between the various altitude constraints so that a minimum of pitch maneuver is required. They are defined by a constant flight path angle and a constant speed. For decelerations, a segment is added in idle thrust just before reaching the speed limit or the speed constraint.
Above the highest constraint defined in descent, the system computes an idle path based on holding of the descent speed and idle thrust + delta. This segment applies up to the cruise flight level where the T/D pseudo waypoint is defined.
The predictions compute the flight plan parameters (time/fuel) based on this path. The total descent time is also computed and from the cruise flight level and the airport elevation, the descent cabin rate is computed and displayed on the MCDU. The crew may then select a desired descent cabin rate. In this case, the system recomputes the descent path to satisfy this new constraint by adding a repressurization segment before the idle path.
The descent path and the predictions are recomputed after each flight plan modification or speed selection change or any destination parameter modification, when the aircraft is not in descent. If the aircraft is in descent phase, the descent path is frozen. It is only recomputed if the lateral flight plan is modified or if a constraint is modified or when the aircraft reaches a holding pattern. Note that a holding pattern is never considered as part of the descent path.
When the aircraft is off the path, the system computes predictions assuming some "return to path" assumption (hold vertical speed if below the path, hold speed in idle and half speedbrakes extended if above the path). If the "return to path" from above does not intercept the path before the next altitude constraint, then a message requesting the extension of speedbrakes is displayed on the EIS displays and the MCDU.
(e) Approach The approach phase starts at the point where the aircraft should decelerate to be able to be at VAPP at 1000 ft. on the final approach segment. The approach profile is then also defined backwards from this last point on the final approach. Idle thrust is assumed on the final until the final intercept altitude is reached. Then idle thrust is assumed in level flight until reaching the descent speed where the DECEL pseudo waypoint is defined.
The various flap/slat configurations are assumed to be extended at the maneuvering speed plus 10 kts. If an altitude constraint exists, an idle descent at constant speed is defined just after the constraint. If a speed constraint exists, a speed hold segment is defined after this constraint until the next point where a deceleration is required to reach the final conditions. Once the approach profile is determined, predictions on the approach are computed and shown on the MCDU.
(8) Vertical guidance Vertical guidance depends on the engaged mode on the FCU. In managed lateral control and managed vertical control, guidance will make the aircraft follow the predetermined profile.
In particular, in climb phase the elevators maintain the predicted speed while the thrust maintains max available thrust. For level segments, the elevators maintain the target altitude which may be the FCU altitude or the altitude constraint displayed on the PFD scale while thrust maintains the climb speed.
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本文链接地址：A320飞机维护手册 AMM AUTO FLIGHT 自动飞行2(65)
