Honeywell SPZ-8000 - Altitude Preselect (ASEL) and VNAV Altitude Preselect (VASEL)

Honeywell
When the altitude hold
MAINTENANCE
MANUAL
GULFSTREAMIV
mode is engaged, the ALT HOLD + TCS
switch opens and clamps the synchronizer output as the
reference
for the mode. With the aircraft on the desired
altitude, the barometric altitude and integrator signals match
each other at the summation point, and no error signal results.
If the aircraft departs from the desired altitude, the
synchronizer output remains unchanged as a reference. The
change in altitude is detected by the air data computer and
compared with the reference altitude clamped in the
synchronizer.
The difference in signals will generate a displacement error
signal to fly the aircraft back to the selected altitude. The
error signal is summed with washed out pitch attitude. Long
term pitch attitude is washed out, so that the aircraft
will
maintain the pilot desired altitude.
The combined altitude reference and pitch attitude washout
signals are filtered, rate limited and summed with
instantaneous vertical velocity (IVV).
The IVV
signal is a control term that helps to stop the
aircraft from departing the desired altitude, and as it comes
back to the desired altitude, the IVV term controls how quickly
the aircraft comes back to reduce overshoot.
The combined altitude command and IVV signals are then TAS gain
programmed to achieve approximately the same aircraft response,
regardless of the aircraft’s airspeed and altitude. The
altitude command signal is routed to Figure 260, sheet 7 and is
processed as discussed in paragraph 3.B.(8)(i).
3. B.
(8) (f) Altitude Preselect (ASEL) and VNAV Altitude Preselect (VASEL)
Modes (Figure 260, sheet 5.)
The ASEL and VASEL modes are automatically armed when the
aircraft is flying toward the preselected altitude or an
altitude constraint. The preselected altitude is input to the
AZ-81O Digital Air Data Computer via the altitude select knob
on the GP-820 Flight Guidance Controller. The master DADC then
transmits the preselected altitude over ASCB to the FZ-820
Flight Guidance Computer and the SG-884 Symbol Generator for
display. The altitude constraint is entered into the FMS
flight plan and sent over ASCB to the FGC by the NZ-920
Navigation Computer.
VSHOLD, FLCH, PITCH HOLD, or VFLCH can be
used to fly to the selected altitude. The arm modes are
annunciated on the PFD by a white ASEL or VASEL.
When the bracket altitude is reached, the system automatically
switches to altitude capture mode.
When the mode captures,
ASEL or VASEL
in green will be displayed on the PFD. The mode
annunciation will be boxed for 5 seconds to indicate the
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Page 298.115
Apr 15/93
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