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The optimum flight level (OPT FL) indicates the most economic flight level for a given cost index,
weight, weather data. It is continuously updated in flight.
The OPT FL is a compromise between fuel and time saving. As a result, the flight crew may
observe jumps in OPT FL due to GW, ISA, or wind changes. The computation of the OPT FL
considers the wind entries made at the different altitudes (normally at the different CRZ FL).
When flying the subsequent CRZ FL, the OPT FL proposed by the PROG page may be affected
by the wind entries made at the previous CRZ FL; these winds are automatically propagated and
may be significantly different from the actual winds.
Note: For simplification purposes, the FCOM/QRH gives the OPT FL at a given Mach number.
It does not consider the cost index, therefore the FMGS and the FCOM/QRH values are
different.
FM displays OPT FL on the PROG page. The PROG page displays dashes for this quantity:
At least ‐ 15 nm before top of descent
‐ When the system detects an engine-out condition
‐ When DES phase is activated.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - OPTIMIZATION
A318/A319/A320/A321 FLEET DSC-22_20-40-10 P 5/16
FCOM 19 AUG 10
OPTIMUM DESCENT PATH
The vertical flight path is computed to minimize fuel consumption, while satisfying the various
altitude constraints and the descent speed profile, in order to reach VAPP at 1 000 ft.
The computer calculates the descent profile before the descent phase is initiated, taking into
account:
‐ All lateral and vertical flight plan data
‐ The descent and approach winds, as inserted into the DESCENT WIND page and PERF APPR
page, and the required maximum cabin rate of descent.
During descent, the descent profile is updated only if the flight plan is modified, or if data for the
APPR phase (WIND, VAPP, or LDG CONF) are changed.
OPTIMIZATION
Applicable to:
The FMGC minimizes cost by optimizing the following items:
‐ Takeoff, approach, and go-around speeds (F, S, Green Dot, VAPP)
‐ Target speed for CLB, CRZ and DES phases (ECON SPD/MACH)
‐ Flight Level (for flight crew's information)
‐ Descent profile from CRZ FL down to the destination airport.
These items depend on the data the flight crew inserts during lateral and vertical flight planning and
revision procedures.
Most are displayed on the PERF pages associated with the appropriate flight phases.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - OPTIMIZATION
A318/A319/A320/A321 FLEET DSC-22_20-40-10 P 6/16
FCOM 19 AUG 10
WIND PROFILE
To obtain the best predictions, the flight crew must enter the wind for the various flight phases and
specifically for waypoints in cruise.
ON GROUND:
During flight planning initialization, enter the winds for the climb and cruise phases using the
HISTORY WIND and WIND pages. Enter, manually or with ACARS, different wind values in
the climb and cruise phases. The system will compute a wind for all waypoints of the F-PLN
using linear interpolation between manual/ACARS entries.
The wind profile will be displayed on the F-PLN B page, and is called forecast wind profile.
Flight crew or ACARS entries are displayed in large font, and system-computed winds in small
font.
IN FLIGHT:
The system updates the predictions and the current ECON speed, using the measured wind at
the present position. It combines actual wind and forecast winds to compute the wind ahead of
the aircraft, but this is totally transparent to the flight crew.
During cruise, the flight crew will enter the descent winds and the approach wind. The system
will update the final predictions, compute the optimum descent profile and compute the
optimum speed in descent and approach.
The forecast wind profile will be used to compute fuel and time predictions, as well as ECON
speed/Mach targets.
OPTIMUM TAKEOFF, APPROACH AND GO-AROUND SPEEDS
The FMGC computes takeoff speeds (F, S, Green Dot) during the preflight and takeoff phases,
using the performance model in the database and the takeoff weight.
The flight crew has to insert V1, VR, and V2 in the PERF TO page manually.
The FMGC uses the performance model and either the predicted landing weight or the current
gross weight at transition to the approach phase to compute approach speeds (VLS, VAPP, F, S,
Green Dot).
On the PERF APPR page, the selected LDG CONF determines the applicable VLS and VAPP,
the latter being updated by the WIND correction that the flight crew enters on the same page. The
FMGC uses the performance model and gross weight to compute go-around speeds (F, S, Green
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A320机组操作手册FLIGHT CREW OPERATING MANUAL 1(117)
