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descent flight path and top of descent. It is therefore part of the managed descent profile.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - OPTIMIZATION
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The flight crew can revert to the optimum speed/Mach by clearing the 3L field.
OPTIMUM FLIGHT LEVEL
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. It ensures a 5 min minimum cruise time,
at a minimum cruise flight level of FL 100.
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 takes
into account the wind entries made by the flight crew, as well as the winds propagated by the FMS
from previously entered 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 when
the system detects an engine-out condition.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - OPTIMIZATION
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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.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - OPTIMIZATION
Intentionally left blank
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A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - COST INDEX
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COST INDEX (CI)
Applicable to: ALL
The cost index is a fundamental input for the ECON SPEED or ECON MACH computation. ECON
SPEED and ECON MACH reduce the total flight cost in terms of flight time and fuel consumption
(and not only in terms of fuel saving).
CI is the ratio of flight time cost (CT) to fuel cost (CF).
CI = CT/CF (kg/min or 100 lb/h).
CI = 0 corresponds to minimum fuel consumption (Max Range).
CI = 999 corresponds to minimum time.
CI = Long Range Cruise (Refer to PRO-NOR-SRP-01-50-B PREPARATION FOR DESCENT AND
APPROACH - COST INDEX FOR LONG-RANGE CRUISE).
Note: The airline's operations department usually defines the cost index, to optimize each
company route. The flight crew does not ordinarily modify the cost index during a flight.
A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - COST INDEX
Intentionally left blank
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A318/A319/A320/A321 FLIGHT CREW
OPERATING MANUAL
AIRCRAFT SYSTEMS
AUTO FLIGHT - FLIGHT MANAGEMENT
PERFORMANCE - PREDICTIONS
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GENERAL
Applicable to: ALL
The FMGC computes predictions for the primary and secondary flight plans and displays them on
the Multipurpose Control and Display Units (MCDUs), and on the navigation display (ND) of the
Electronic Flight Instrument System (EFIS).
The computations use the current state of the aircraft (GW, CG, position, altitude, speed, engaged
mode of the autopilot or flight director, time, wind, temperature) for the active flight plan.
The computations use data entered by the flight crew for the secondary flight plan when it is not a
copy of the active flight plan. When the secondary flight plan is a copy of the active flight plan, it uses
the same data.
PREDICTIONS FOR THE PRIMARY FLIGHT PLAN
Applicable to: ALL
The predictions displayed on the MCDU assume that the FMGS will guide the aircraft along the
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A320机组操作手册FLIGHT CREW OPERATING MANUAL 1(120)
