Consideration of HM Leg in Predictions
Figure 022
Aircraft on Profile (Nominal Case)
Figure 023
Aircraft on Profile (Reversion Mode) - Hold of Lower Speed Margin
Figure 024
Aircraft above Profile - Hold of Upper Speed Margin
Figure 025
Aircraft below Profile
Figure 026
-Mode requested If the descent profile is available, the guidance mode requested by the FM part is DESCENT unless an altitude constraint requests a level segment as described in predictions. During a recomputation of the descent profile, vertical auto control is not available as long as new profile is not defined (Reference path altitude displayed).
If DES mode is active, the guidance submodes and their reversion logic depend on the position of the A/C versus profile.
-A/C on or above profile On the idle path, guidance initially holds precomputed path on elevator and precomputed thrust. On the geometric path or repressurization segment, the descent path is also maintained but thrust holds the ECON speed. Due to error in weather forecast or engine thrust modelling, speed can vary. As long as speed remains within speed margin, initial guidance submodes and targets are maintained. If the lower margin is reached, then thrust is applied to maintain this lower margin. If the upper margin is reached, then, after having confirmed that idle thrust is set, the aircraft diverges from the descent path by maintaining this upper speed margin on elevator. Descent path control is recovered if the aircraft intercepts the descent path again. The guidance submodes and their associated targets can therefore be:
-----------------------------------------------------------|ELEVATOR| VPATH | SPD | | Target | precomputed path |upper speed margin| |--------|-----------------------------|------------------|
| | THR | THR | SPD | SPD | THR |
| Thrust | Precom-| idle| econ | lower | idle |
| Target | puted | | speed| speed | |
| | thrust | | | margin| |
-----------------------------------------------------------
(Ref. Fig. 023, 024, 025)
-A/C below profile
The active submode and the related targets are the ones
used in prediction computations from the present position.
The selected submode can therefore be:
------------------------------------------| Elevator | V/S | V/S | | target | - 1000 ft/mn | - 500 ft/mn | | | | | |----------|-----------------------------| | Thrust | SPD | | target | ECON descent guidance speed | ------------------------------------------
(Ref. Fig. 026)
-A/C before HM and in HM
A few NM before entering the HM leg, the speed target
becomes the holding speed, the thrust is set to idle.
In the HM leg, it is as described in predictions.
---------------------------------------------| Elevator | SPD | V/S | | target | holding speed | - 1000 ft/mn | |----------|---------------|----------------| | Thrust | THR | SPD | | target | idle | holding speed | ---------------------------------------------
NOTE : If ALT ACQ or ALT mode is active, the speed target
____ is the ECON descent speed or in HM leg, the holding speed
NOTE : The message MORE DRAG is displayed on the PFD when
____ the A/C is above profile only when predictions locate profile interception close to an altitude constraint (Ref. Fig. 025)
5 Approach
_ a approach parameters
_
-approach speeds The FM computes F, S, Green Dot, VLS and VAPP which are displayed on the APPR page. The VAPP can be modified by the pilot on the MCDU (Ref. para. 2.B.). (Ref. Fig. 027) The VAPP is used by the autothrust function as target speed from the glide track phase.
-the final capture altitude depends on the selected approach and comes from the Data base. If no final capture altitude is defined in the Data base, a default value of 1500 ft above landing elevation is used.
APPROACH (APPR) Pages
Figure 027
b
_
c
_ d
_
-final slope also depends on the selected Approach procedure and comes from the Data base. If no value is defined, a default value of - 3. is used.
-landing configuration The pilot can preselect, on the APPR page, the landing configuration either FULL which is the default one or CONF 3. It is used internally for predictions and guidance. (Ref. Fig. 027)
-Decision Height (DH) If an LS approach or an LS guidance mode is selected, the pilot has to enter a DH value or NO on the APPR page (field 3R). It is displayed on the PFD.
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