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Flight Management System (FMS) for the Agusta AW139/AB139 Helicopter
VFLCH is used by the FMS during all climbs and, unless a path is
defined, during descents. VFLCH is set as the active mode when the
altitude preselector is above or below the current aircraft altitude and
the current flight director mode is not altitude hold. When in other
modes of VNAV, a transition to VFLCH is made by setting the
indicated airspeed (IAS) preselector to other than current altitude
and pushing the FLCH button on the guidance panel.
NOTE:
When VNAV is disengaged while in VALT, the flight
director mode becomes PITCH HOLD, not altitude hold.
VNAV Path (VPATH) -- This mode is vertical path. In this mode, FMS
D
provides guidance along a geometric path. VNAV controls the
aircraft along a geometric path downward to a waypoint altitude
constraint. The path angle is either an FMS computed value,
procedure specified, or pilot--entered. Path descents are identical to
instrument landing system ( ILS) approaches where the glideslope
gives a constant angle descent. VNAV gives the same constant
angle descent using barometric altitude to determine when the
aircraft is on path.
The primary objective during VPATH descents is maintaining the
geometric path. To maintain the geometric path, VNAV computes
the required vertical speed to maintain the path. VNAV then sends
the command to the FGC. The FGC adjusts the pitch of the aircraft
to maintain the requested vertical speed. During VPATH operations,
the aircraft speed increases or decreases to maintain the path.
Vertical Glide Path Mode (VGP) -- The vertical glide path (VGP)
D
mode permits crew management of the altitude preselector during
FMS managed nonprecision approaches. When using standard
VNAV during nonprecision approaches, dialing the altitude
preselector to the minimum descent altitude (MDA) during the final
approach segment is necessary. When a missed approach is
executed, resetting the altitude preselector to the missed approach
altitude is necessary. With the VGP mode, the altitude preselector
is set to the missed approach procedure altitude once the VGP
mode is engaged. The FMS manages the aircraft on a vertical path
to the missed approach point (MAP) regardless of the setting of the
altitude preselector. This is similar in concept to glideslope capture
for ILS approaches.
A28- - 1146- - 181
REV 3 Mar 2009
Honeywell International Inc. Do not copy without express permission of Honeywell.
Flight Plan
7-25
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