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In manual speed control, the Speed/Mach switching is automatic and controlled by the FM part according to the switching altitude. Upon switching, the FCU displays the Mach number (or speed) which corresponds to the speed (or Mach number) selected and to the switching altitude. This automatic switching can be overriden by the pilot through action on related pushbutton switch (on the FCU) and upon switching, the display is synchronized on the A/C Mach number (or speed).
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Target Speed Limitations The speed control permits to limit the target speed within a margin which guarantees the maneuverability and safety with respect to the stalling speed and maximum speed. The lower limit is the minimum selectable speed VLS which is 30% higher than the stalling speed. The upper limit is the maximum operating speed which corresponds to the structural limits or to buffeting. In managed speed control, when the target speed is determined by the FM part (i.e. outside the takeoff, landing and go around phases), the lower limit is the maneuvering speed (VMAN) 45% higher than the stalling speed. All these typical speeds are calculated by the FAC. Their definitions and the guarantees they provide are described in 22-60-00 : FAC.
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Synchronization of the SPD MACH Display of the FCU When the managed speed control is engaged, the SPD MACH window of the FCU displays dashes and the associated automatic control light is on. (Ref. Fig. 001) (item A) When in managed speed control, if you turn the SPD MACH selector knob on the FCU, the FMGC causes the synchronization of the FCU SPD MACH window. (Ref. Fig. 001) (item B) The value to be synchronized is calculated and transmitted by the FMGC to the FCU. Then, if the pilot pulls the SPD MACH selector knob, the manual speed control is engaged and the selected speed is taken into account. (Ref. Fig. 001) (item C) If the pilot does not pull the SPD MACH selector knob within the 10 s which follow the selection, the dashes are displayed again in the window and the selection is lost. The different possibilities of synchronization are:
(a) Display of a reference in the display window which can be caused:
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by the loss of the two FMGCs ; in this case, the window displays only the speed, and the synchronized value will be the last acquisition of the A/C speed before the loss of the two FMGCs.
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by the engagement of the manual speed control or turn action on the SPD MACH selector knob. The synchronized value is the aircraft speed or Mach (e.g. energization of AFS or takeoff without V2). At takeoff or in go around, the synchronized value cannot be lower than "V2 memorized" or "GA speed target".
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-by acceptance of a preset value entered on the MCDU. When the pilot presets a speed or Mach value on the MCDU for the next flight phase when there is an FMS phase change, the manual speed control is selected and this value is displayed on the FCU.
(b) Modification of the speed or Mach reference displayed in the window, caused by the FMGC:
-when the pilot has preset a speed or Mach value on the MCDU for the next flight phase, at the FMS phase change, this value is synchronized
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during climb when the aircraft reaches the SPD-to-MACH switching altitude, the synchronized value is the Mach number calculated by the FMS (Mach number which corresponds to the selected speed and to the switching altitude).
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during descent when the aircraft reaches the MACH-to-SPD switching altitude, the synchronized value is the speed calculated by the FMS.
-when the pilot causes a Speed/Mach switching through action on the related pushbutton switch (on the FCU), the synchronized value is the aircraft speed or Mach number.
NOTE : Display unit limitations:
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between 100 and 399 kts for speed
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between 0.01 and 0.99 for Mach number.
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B. Lateral Modes (Ref. Fig. 002) The figure gives:
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the list of lateral modes active in cruise,
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the control laws and references associated with each mode.
(1) Heading or Track Hold Modes (HDG/TRK) (Ref. Fig. 003) (item A) The choice between heading and track modes is made according to the selection made on the FCU. After an in-flight energization, the FCU selection is HDG-V/S and the heading hold mode is engaged at the FD. An action on the FCU related pushbutton switch causes the selection of TRK-FPA, engagement of the TRK mode and the synchronization of the HDG TRK window on the aircraft track. A second action on the FCU related pushbutton switch causes the selection of HDG-V/S, engagement of the HDG mode and the synchronization of the HDG TRK window on the aircraft heading. These logic is valid if the aircraft, with HDG or TRK mode active, is not turning (current target < 5 deg). If not, an action on FCU related pushbutton switch leads to take the previous target for the new one. So the turn is not interrupted. (Ref. Fig. 003) (item B).
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