Intentionally left blank
 
NORMAL OPERATIONS
DESCENT
 
PREFACE
Applicable to: ALL
The PF will set preferably the MCDU PROG or PERF page as required (PROG page provides VDEV in NAV mode and BRG/DIST information, PERF DES page provides predictions down to any inserted altitude in DES/OP DES modes) whereas the PNF will set the MCDU F-PLN page.
In mountainous areas, the selection of the TERR ON ND sw enhances pilot awareness and can be used in any flight phase.
If use of radar is required, consider selecting the radar display on the PF side and TERR on PNF side only.
COMPUTATION PRINCIPLES
Applicable to: ALL
TOD AND PROFILE COMPUTATION
The FMGS calculates the Top Of Descent point (TOD) backwards from a position 1 000 ft on the final approach with speed at VAPP. It takes into account any descent speed and altitude constraints and assumes managed speed is used. The first segment of the descent will always be idle segment until the first altitude constraint is reached. Subsequent segments will be "geometric", i.e. the descent will be flown at a specific angle, taking into account any subsequent constraints. If the STAR includes a holding pattern, it is not considered for TOD or fuel computation. The TOD is displayed on the ND track as a symbol:
Descent path
 
The idle segment assumes a given managed speed flown with idle thrust plus a small amount of thrust. This gives some flexibility to keep the aircraft on the descent path if engine anti-ice is used or if winds vary. This explains THR DES on the FMA.
The TOD computed by the FMS is reliable provided the flight plan is properly documented down to the approach.
 
NORMAL OPERATIONS
DESCENT
 
MANAGED DESCENT SPEED PROFILE
The managed speed is equal to:
? The ECON speed (which may have been modified by the crew on the PERF DES page, before entering DESCENT phase), or
? The speed constraint or limit when applicable.
GUIDANCE AND MONITORING
Applicable to: ALL
INTRODUCTION
To carry out the descent, the crew can use either the managed descent mode (DES) or the selected descent modes (OP DES or V/S). Both descent modes can be flown either with selected speed or managed speed.
The modes and monitoring means are actually linked.
The managed DES mode guides the aircraft along the FMS pre-computed descent profile, as long as it flies along the lateral F-PLN: i.e. DES mode is available if NAV is engaged. As a general rule when DES mode is used, the descent is monitored using VDEV called "yoyo" on PFD, or its digital value on the PROG page, as well as the level arrow on the ND.
The selected OP DES or V/S modes are used when HDG is selected or when ALT CSTR may
　
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