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and it is based upon the managed descent speed profile. It does not take holding patterns into
consideration.
The descent profile has several segments:
A repressurization segment. When necessary, this produces a repressurization ‐ rate for the cabin
during descent. It is a function of the destination airport altitude and the selected cabin rate
(defaulted to - 350 ft/min but this can be modified)
‐ Idle path segment. The AP/FD controls the speed and the autothrust stays at idle thrust. The
guidance computes this profile from the top of descent or the end of the repressurization segment
to the first vertical constraint that cannot be flown at idle thrust
‐ Geometric path segments. The AP/FD controls the vertical path, and autothrust controls the
speed. These segments take the aircraft from the first constraint to the deceleration point.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT GUIDANCE
AP/FD VERTICAL MODES - DESCENT MODE
A318/A319/A320/A321 FLEET DSC-22_30-70-50 P 2/22
FCOM 19 AUG 10
The descent mode is a managed mode that may be engaged during cruise. It can be armed or
engaged in descent and approach phases (except if the FCU selected altitude is higher than the
present aircraft altitude).
GENERAL
Applicable to:
,
,
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The DES mode guides the aircraft along the descent path computed by the FMGS. The system
computes this flight path backwards from the deceleration point up to the top of descent (T/D), with
respect to the speed and altitude constraints at the deceleration point, the guidance begins the
deceleration to VAPP, to be reached at 1 000 ft above touchdown on the final descent path.
Internally, the computer divides the descent path into various segments, depending on the relative
positions of the constraints. It starts at top of descent (T/D) by setting up an “idle” segment that
takes the aircraft down to the first constraint, and follows this with “geometric” segments between
constraints.
The current geometric path segment can be replaced by an idle path segment in case of:
‐ Modification of CI
‐ Entry or modification of DES auto MACH/SPD on PERF DES page
‐ Insertion of a DIR TO (including ABEAM, RADIAL IN and RADIAL OUT)
‐ Entry or modification of an attitude constraint on the active segment.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT GUIDANCE
AP/FD VERTICAL MODES - DESCENT MODE
A318/A319/A320/A321 FLEET DSC-22_30-70-50 P 3/22
FCOM 19 AUG 10
The descent profile takes into account wind data and data from the lateral and vertical flight plans,
and it is based upon the managed descent speed profile. It does not take holding patterns into
consideration.
The descent profile has several segments:
A repressurization segment. When necessary, this produces a repressurization ‐ rate for the cabin
during descent. It is a function of the destination airport altitude and the selected cabin rate
(defaulted to - 350 ft/min but this can be modified)
‐ Idle path segment. The AP/FD controls the speed and the autothrust stays at idle thrust. The
guidance computes this profile from the top of descent or the end of the repressurization segment
to the first vertical constraint that cannot be flown at idle thrust
‐ Geometric path segments. The AP/FD controls the vertical path, and autothrust controls the
speed. These segments take the aircraft from the first constraint to the deceleration point.
The descent mode is a managed mode that may be engaged during cruise. It can be armed or
engaged in descent and approach phases (except if the FCU selected altitude is higher than the
present aircraft altitude).
ARMING CONDITIONS
Applicable to: ALL
The DES mode is armed when an ALT CSTR is captured and all the following conditions are met:
‐ FCU selected altitude is lower than present altitude
‐ NAV, LOC* or LOC mode is engaged
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT GUIDANCE
AP/FD VERTICAL MODES - DESCENT MODE
A318/A319/A320/A321 FLEET DSC-22_30-70-50 P 4/22
FCOM 19 AUG 10
‐ Takeoff or go-around phase is not active
‐ Flight profile is available.
DISARMING CONDITIONS
Applicable to: ALL
The DES mode is disarmed if one of the following conditions is met:
‐ Engagement of another vertical mode
‐ FCU selected altitude is set above the aircraft current altitude
‐ Loss of NAV, LOC*, or LOC mode
‐ Switching to the go-around phase
‐ Loss of vertical flight path validity
‐ Setting the FCU selected altitude at an altitude constraint while ALT CST* was engaged. (ALT*
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A320机组操作手册FLIGHT CREW OPERATING MANUAL 2(90)
