DES Mode: Aircraft on Profile, in SPEED AUTO CONTROL
Figure 021
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When DES mode is armed or engaged, speed margins are used
for display and guidance as described above. The AIRBRAKES
message is displayed on the PFD when a deceleration is
required above path or on a steep path segment, to request
pilot action.
These figures:
(Ref. Fig. 021, 022, 023, 024)
apply when DES mode and SPEED AUTO CONTROL are both active.
(f) APPROACH phase
1 Approach parameters
_
(Ref. Fig. 025, 026)
a Landing configuration
_ The landing configuration must be selected manually on the PERF APPROACH page. It can be either FULL (by default) or configuration 3. It is used to compute approach speeds and is transmitted to the GPWS.
b Approach speeds
_ VFTO, F, S, VLS for the selected landing configuration and VAPP are computed and displayed on the PERF APPROACH page. VAPP can be modified by the pilot. When computed by the system, VAPP = VLS + MAX(5, MIN(15,headwind x 0.3)) Kts, where "headwind" is the positive component on the runway axis of the destination wind entered on the PERF APPR page.
c Decision Height (DH) and Minimum Descent Altitude or Height
_ (MDA/MDH) When a RNAV, VOR or NDB approach exists in the flight plan, only MDA or MDH can be entered. It is either MDA or MDH depending on FMGC pin programming. Otherwise DH can also be entered and "NO" DH entry is allowed. DH and MDA or MDH entries are mutually exclusive. When defined, the pilot DH, MDA or MDH entry is displayed on the PFD during DESCENT and APPROACH phases.
2 Theoretical approach profile
_ (Ref. Fig. 027, 028) The theoretical approach profile is built according to flight plan altitude, flight path angle, and speed constraints, backwards from the last point of the approach (runway threshold, missed approach point or the airport) up to the DECEL pseudo-waypoint.
Constant slope segments are constructed for flight path angle constraints. The specified angle is used unless an altitude constraint requires a higher slope. Constant speed, idle thrust segments are constructed for level change between altitude constraints, unless a flight path angle is specified. VAPP is held up to 1000 ft AGL. To compute the speed profile from VAPP, idle thrust is assumed with the right configuration to accelerate backwards to the descent speed, at which point the DECEL is located. Speed constraints are taken into account: constant speed segments are assumed, whenever required, in order to meet them.
3 Predictions
_ Predictions are based on the theoretical approach profile, like in DESCENT phase and with the same assumptions as for the geometric path.
4 Guidance
_
a DES mode
_ It can be armed or engaged under the same conditions as in DESCENT phase. However, there are no speed margins in approach. Depending on aircraft computed position and actual speed, selected submode can be:
----------------------------------------------------------------------| | above path | | | below path | | DES mode | or | On path | below path | or in an HM | | |overspeeding| | | | ----------------------------------------------------------------------| Elevator | SPEED | VPATH | FPA | V/S | | target | | | | | |-----------|------------|-----------|--------------|----------------| | Thrust | THRUST | SPEED | SPEED | SPEED | | target | | | | | ----------------------------------------------------------------------
b FINAL mode
_ (Ref. Fig. 026) It can only be armed for a non-precision approach: VOR, RNAV or NDB, unless at least one RMP is active.
DES Mode: Aircraft on Idle Path,
Underspeeding in SPEED AUTO CONTROL
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