-weight,
-weather conditions,
-cost index entered in the MCDU. The cost index which is the ratio between the time cost and the fuel cost indicates to what extent one of these parameters must be privileged with respect to the other. The CAS/Mach switching is commanded by the FM part when the aircraft reaches the switching altitude which corresponds to the optimum speed and Mach of the managed speed control. The elaboration of the longitudinal flight plan and control in the vertical plane are described in 22-73-00 -Performance/Vertical Functions.
(c) Operational use
1_ Engagement
The engagement of the level-change managed modes is possible
only if a longitudinal flight plan is available in the flight
management part and if the horizontal NAV mode is active on
the AP/FD.
The CLB or DES mode is engaged or armed through push action on
the altitude knob on the FCU.
(Ref. Fig. 031)
When the CLB and DES modes are active:
- dashes are displayed in the V/S FPA window of the FCU
display,
- the white LVL/CH light comes on on the FCU display.
2_ Arming of the CLB and DES modes
(Ref. Fig. 032)
The level-change managed modes enable to meet the altitude
constraints which may appear in the longitudinal flight plan.
When the capture of an altitude constraint requires leveling
off of the aircraft the ALT ACQ mode is activated and the CLB
or DES mode is armed.
The altitude constraint is displayed in magenta on the
altitude scale of the PFD together with the ALT or ALT *
messages armed or active on the FMA.
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Managed Level Change When A/C Altitude < Selected Altitude
Figure 031
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1
Managed Level Change - Leveling Off Caused by an Altitude Constraint
Figure 032
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When the constraint is released, the FM part commands the activation of the CLB or DES mode for continuation of the flight plan.
3 Disengagement
_ (Ref. Fig. 033, 034) The managed level-change control modes are disengaged if there is a discontinuity in the longitudinal flight plan or if the NAV mode is lost. (Ref. Fig. 033) The same situation is present if the flight phase determined by the FM part becomes incompatible with the CLB or DES mode active. (Ref. Fig. 034) In these conditions, the reversionary mode engaged at the AP/FD will be V/S-FPA and synchronization of the vertical speed/flight path angle in the FCU display will permit to avoid an abrupt change of flight path, except in CLB where the reversionary mode will be OPEN CLB. These conditions also cause disarming of the CLB or DES modes when the AP/FD is in altitude hold mode on a constraint. Finally, the CLB and DES modes active are lost if another longitudinal mode is engaged at the AP/FD or if the pilot selects a level on the FCU lower than the aircraft-in-climb level or higher than the aircraft-in-descent level (Ref. V/S FPA modes).
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