SPEED CONSIDERATION VAPP
The approach speed (VAPP) is defined by the crew to perform the safest approach. It is function of gross weight, configuration, headwind, A/THR ON/OFF, icing and downburst.
In most cases, the FMGC provides valuable VAPP on MCDU PERF APPR page, once tower wind and FLAP 3 or FLAP FULL landing configuration has been inserted (VAPP = VLS + max of {5 kt, 1/3 tower head wind component on landing RWY in the F-PLN}).
The crew can insert a lower VAPP on the MCDU APPR page, down to VLS, if landing is performed with A/THR OFF, with no wind, no downburst and no icing.
He can insert a higher VAPP in case of strong suspected downburst, but this increment is limited to 15 kt above VLS.
In case of strong or gusty crosswind greater than 20 kt, VAPP should be at least VLS +5 kt; the 5 kt increment above VLS may be increased up to 15 kt at the flight crew's discretion.
The crew will bear in mind that the wind entered in MCDU PERF APPR page considers the wind direction to be in the same reference as the runway direction e. g. if airport if magnetic referenced, the crew will insert magnetic wind.
The wind direction provided by ATIS and tower is given in the same reference as the runway
direction whereas the wind provided by VOLMET, METAR or TAF is always true referenced. VAPP is computed at predicted landing weight while the aircraft is in CRZ or DES phase. Once the approach phase is activated, VAPP is computed using current gross weight.
Managed speed should be used for final approach as it provides Ground Speed mini (GS mini) guidance, even when the VAPP has been manually inserted.
NORMAL OPERATIONS
APPROACH GENERAL
GROUND SPEED MINI PURPOSE
The purpose of the ground speed mini function is to keep the aircraft energy level above a minimum value, whatever the wind variations or gusts.
This allows an efficient management of the thrust in gusts or longitudinal shears. Thrust varies in the right sense, but in a smaller range (± 15 % N1) in gusty situations, which explains why it is recommended in such situations.
It provides additional but rational safety margins in shears.
It allows pilots "to understand what is going on" in perturbed approaches by monitoring the target speed magenta bugs: when target goes up = head wind gust.
COMPUTATION
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本文鏈接地址：A330/A340 機組訓練手冊 FCTM Flight Crew Training Manual 1(65)
