AP Engagement with FD in ALT Mode
 Figure 017

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 ALT HOLD Control Law
 Figure 018
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 a_ Vertical speed: this sub-mode is activated when the AP is
 engaged, with the altitude mode already active on the
 flight director.
 This control mode cancels the aircraft vertical speed using
 the vertical speed control law.

 b Altitude: this sub-mode is engaged:
_
 -
when the altitude mode is activated,

 -
when the vertical speed is cancelled with the vertical speed sub-mode engaged.

 -This control mode uses the ALT HOLD control law and its reference is one of the altitudes defined below:
 -
The reference altitude of the altitude acquire mode when the altitude mode is activated.

 -
The aircraft altitude when the vertical speed is cancelled as a result of AP engagement with the mode active on the flight director.

 NOTE : As the ALT HOLD control law uses the IRS ZBI
____ parameter, the level hold is not disturbed by a barometric pressure change (QNH or QFE) or Baro/standard switching.
 (3) Manual Control Modes for Level Changes The three manual control modes for level changes are:
 -V/S - FPA

 -OPEN CLB, OPEN DES

 -EXP CLB, EXP DES.
 These modes can be engaged in flight, 5 seconds after lift-off or on
 the ground, with engines stopped.

 (a) Vertical speed hold mode or flight path hold mode (V/S or FPA). (Ref. Fig. 019) The choice between the V/S and FPA modes depends on the selection made on the FCU and is described in Para. 2. B. (1). At each switching, the V/S FPA window of the FCU display is synchronized on the aircraft parameter.
 1 Characteristics
_ The V/S FPA mode permits to acquire and hold the vertical speed or flight path displayed in the V/S FPA window of the FCU display. The speed hold must be ensured by the thrust control.
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 V/S FPA Mode Selection
 Figure 019

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 2
_
 3
_
Operational use
 (Ref. Fig. 020)
 The V/S FPA mode is automatically engaged, upon in-flight
 energization of the FMGC, through FD engagement.
 The V/S FPA mode can be engaged through pull action on the
 corresponding FCU selector knob.
 This action will cause synchronization of the V/S FPA window
 on the aircraft parameter which will be used as a reference.
 A preselection of vertical speed or flight path angle is
 possible when you turn the related selector knob.
 This causes the synchronization of the V/S FPA window on the
 aircraft parameter.
 This value can then be modified.
 If the V/S FPA mode is not engaged within the 45 seconds which
 follow the end of the preselection, the latter is lost.
 With the ALT mode active on the AP/FD, the V/S FPA mode can be
 engaged even if the selected altitude has not been modified.
 This means that with this mode it is possible to deviate from
 the level selected on the FCU (in this case, the ALT ACQ mode
 is not armed).
 If the pilot engages the AP while the V/S FPA mode is engaged
 on the F/D alone, the FCU window is synchronized on the
 aircraft parameter.
 Then, even if the pilot has not followed the flight director,
 engagement of the AP does not cause any sharp modification of
 the aircraft flight path.

 NOTE : When the aircraft performances no longer permit to

____ ensure speed or Mach hold considering the great V/S or FPA values selected, the OPEN CLB or OPEN DES mode is engaged automatically (Ref. Para. 2.C.(3)(b)).
Altitude hold in V/S FPA mode
 (Ref. Fig. 021)
 When the pilot selects 00 in the V/S FPA window of the FCU,
 the AP/FD provides a guidance in V/S FPA mode which permits to
 hold the altitude obtained after cancellation of the vertical
 speed.
 This type of guidance is cancelled as soon as the selected
 parameter becomes again different from zero.
 When it is active, the ALT indication appears on the FMA.
 When it is active, and when the DMC CPIP3 is pin programmed,
 the VS=0 or FPA=0 indication appears on the FMA.
 This feature is achieved via a pushing action on the vertical
　
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