Vnav Path (Vpath) Mode - Honeywell SPZ-8000 Maintenance Manual

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3. B. (8) (d)
In
the first instance, with the pilot retarding the speed
bug
reference, selected IAS/Mach is compared against actual
IAS/Mach.
The difference is changed to a rate term and then
converted to an altitude rate term.
This signal is routed
through a zero vertical
speed limiter, pitch rate limiter, TAS
gain programmer, and sent to Figure 260, sheet 7 as the FLCH or
VFLCH command. This signal determines what is the aircraft's
commanded vertical
speed as the system maintains the IAS/Mach
reference. As the aircraft flies to the commanded vertical
speed, actual altitude rate is summed against the command to
center the flight director command cue. Actual airspeed or
Mach is routed through a rate taker and is gain changed to act
as a damping term on the command signal.
In the second instance, with the mode engaged and the speed bug
synchronized to existing aircraft speed, the pilot advances the
throttles to maintain the speed reference during the FLCH or
VFLCH maneuver. Initially, the aircraft starts to accelerate.
The increase in TAS and longitudinal acceleration is changed to
a potential speed rate, with normal acceleration added as a
damping term. This potential speed rate is changed to an
altitude rate signal and the commanded vertical speed signal is
processed as previously discussed and is routed to Figure 260,
sheet 7 and is processed as discussed in paragraph 3.B.(8)(i).
The FMS (and air data) information is used from the same side
FMS and DADC as are selected for display on the in-command side
PFD. If FMS is not selected for display, the DAFCS selects the
FMS on the same side as the PFD in-command.
VNAV Path (VPATH) Mode (See Figure 260, sheet 3.)
The VPATH mode is used to descend to a new flight level at a
prescribed angle (1 to 6 degrees). Activation of VPATH mode is
automatic from the coupled FMS. The FMS calculates a top of
descent (TOD) based on the altitude constraints entered into
the FMS flight plan and the desired or calculated path angle.
The VNAV path mode is annunciated on the PFD by a green VPATH.
Commands to maintain the aircraft on the prescribed path are
based on the target vertical speed received from the coupled
FMS over ASCB. Note that this-target is not displayed
GP-820 Flight Guidance Controller. The vertical speed
on the GP-820 will be blanked except in vertical speed
which is discussed in paragraph 3.B.(8)(b).
Prior to mode engagement or use of TCS, altitude rate
on the
display
mode,
information provided by the AZ-81O DADC through ASCB is fed to
a summing point where it is compared to altitude rate. The
signals cancel so that there is no error signal. Upon mode
engagement or release of TCS, the aircraft altitude rate is
compared with the FMS commanded vertical speed. Should a
difference between these signals occur, the difference is TAS
22-14-00
Page 298.113
Aug 15/91
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