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is used to "catch up" with the ideal profile, when cleared for descent.
In DES mode, there is a target speed with high and low speed brackets. Speed will vary
between these brackets to maintain the airplane on the required descent path. The speed
will vary because the actual conditions (wind, temperature, use of anti-ice etc.) will differ from
the assumptions made by the FMGS. If the speed decays towards the lower bracket, power
will be applied to maintain the programmed path and MACH (SPEED) is annunciated in the
FMA. Should the speed rise to the upper bracket, and it is computed that the required profile
will not be regained, a white MORE DRAG message is displayed. The PROG page and on
the ND, the level symbol should be used to monitor progress in the descent.
Under normal circumstances, thrust will be at idle. However, if a slow descent is required, or
the speed has decayed then the thrust mode changes to speed. Similarly, if a speed
increase is required (maybe due to ATC) then using a selected speed in excess of optimum
will command the autothrust to speed mode, as the aircraft applies power to keep on profile.
If an increased rate of descent is required, OPEN DES must be selected and speedbrake
used as appropriate. Selecting only speedbrake in DES mode will not achieve an increase in
rate of descent, as power will be applied to maintain the airplane on profile and at target
speed.
OPEN DESCENT
An alternative to the managed descent is the OPEN DES mode. This will give a descent with
thrust at idle, and retains the option of using a managed speed or a pilot selected speed.
Speedbrake is very effective in increasing descent rate. If the aircraft is not in managed
navigation, i.e. in HDG mode, then managed descent mode is not available. The aircraft will
not follow a descent path but will merely descend at an idle thrust setting, and a set speed.
By monitoring the ND, the level off point can be found and the PROG page gives a deviation
from planned profile. If in HDG mode, then the PROG page displays required miles to
touchdown and actual miles.
A319/A320/A321
FLIGHT CREW TRAINING MANUAL
1.02.17 Page 2
REV 21 MAY 98
NORMAL OPERATION BRIEFINGS
DESCENT
- PROCEDURES AND TECHNIQUES -
CHAP02\17
05 - TRAINEES’ ACTIONS (END)
RECOVERING IDEAL PROFILE
If the airplane is below profile in the OPEN DES case, the simplest way of regaining the
profile is to use V/S. Once on the profile again, adjust rate of descent accordingly, with
speed, V/S changes or OPEN DES.
If high on profile in the OPEN DES case, speed may be increased (with the permission of
ATC), or drag used. Note that in DES mode, if drag is used when attempting to steepen
profile, the airplane will apply power to offset the drag and maintain the ideal profile. Thus, to
increase descent rate, OPEN DES must be selected and drag used, ensuring that thrust
remains at idle.
EXPEDITE DESCENT (A320 only)
Another option is to use the EXPED pb which will command target speed close to
MMO/VMO. This will give a very high rate of descent and its use must be closely monitored.
OVERVIEW
In all modes the ideal profile is tracked by the VDEV indicator on the PFD. It is important at
all times to bear in mind terrain and MEA considerations. The procedure for terrain checking
is especially important with thrust at idle. Bear in mind the drill for recovery from GPWS
warnings QRH 1.08 (GPWS Warning).A rule of thumb calculation for descent is that track
miles to run should equal three times your height in thousands of feet. Exact figures are
given in QRH 4.10.
The effects of engine and wing anti-ice on descent profile can be marked, as the idle N1/EPR
is increased, thus giving a shallower descent profile. If already in the descent, and anti-ice is
used, it is usual to see an increase in speed in DES mode. If speed increases to the upper
bracket, speedbrake can be used. If in OPEN DES mode a higher selected speed is
advisable. Alternately, in OPEN DES mode, half speedbrake will counteract the effects of
anti-ice. Conditions requiring the use of anti-ice are listed in FCOM 3.04.30 (Supplementary
Techniques - Ice and Rain Protection).
It is vital to know the operating mode of the thrust system, particularly with regard to CFIT.
Weather radar use in the descent is covered in FCOM 3.03.17(SOPs - Descent).
06 - COMPLETION STANDARDS
· Uses the correct method to initiate descent.
· Monitors descent according to expected navigation.
· Maintains heading +/-5 and speed +/-10 kts.
· Adjusts descent rate using appropriate methods bearing in mind aircraft limitations and
passenger comfort.
· Complies with all ATC clearances and minimum safe altitudes.
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