NORMAL OPERATIONS
APPROACH GENERAL
A318/A319/A320/A321
FLIGHT CREW TRAINING MANUAL
COMPUTATION
This minimum energy level is the energy the aircraft will have at landing with the expected tower wind; it is materialized by the ground speed of the aircraft at that time which is called GS mini: GS mini = VAPP - Tower head wind component
In order to achieve that goal, the aircraft ground speed should never drop below GS mini in the approach, while the winds are changing. Thus the aircraft IAS must vary while flying down, in order to cope with the gusts or wind changes. In order to make this possible for the pilot or for the A/THR, the FMGS continuously computes an IAS target speed, which ensures that the aircraft ground speed is at least equal to GS mini; the FMGS uses the instantaneous wind component experienced by the aircraft:
IAS Target Speed = GS mini + Current headwind component
This target speed is limited by VAPP in case of tailwind or if instantaneous wind is lower than the tower wind.
example
NORMAL OPERATIONS
APPROACH GENERAL
A318/A319/A320/A321
FLIGHT CREW TRAINING MANUAL
GROUND SPEED MINI
Criteria: P7373, P7519, P7666, SA
9 Applicable to: MSN 1668-4078
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
This minimum energy level is the energy the aircraft will have at landing with the expected tower
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本文鏈接地址：A318/A319/A320/A321 機組訓練手冊 FCTM Flight Crew Training Manual(94)
