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Flight Management System (FMS) for the Agusta AW139/AB139 Helicopter
VNAV PATH DESCENT (VPATH)
The elements of a VNAV path descent profile are shown in Figure 7--24.
A VNAV path descent is flown from VALT at any time when the altitude
preselector has been dialed down before the TOD point is reached. The
VNAV path descent mode is used to descend to a new flight level at a
calculated or prescribed angle (between 1_ and 6_). The following
steps apply:
An altitude constraint is entered at a waypoint (1). The FMS
D
calculates an angle and TOD (2) for the path descent.
At the TOD, the flight guidance computer switches from VALT to
D
VPATH and begins a descent (2).
The altitude preselector is set to the ATC cleared altitude (3).
D
One minute before reaching the TOD, the vertical deviation scale is
D
displayed on the EFIS. When the altitude preselector is not at a
lower altitude, the message RESET ALT SEL? is displayed.
The VNAV angle is always displayed on MCDU for path descents. The
path is always followed except when the aircraft speed approaches the
following:
V
/M
D
MO
MO
VNAV tries to satisfy both the altitude preselector and the waypoint
constraint altitude. However, VNAV never flies through the altitude
preselector.
Flight Plan
7-44
Honeywell International Inc. Do not copy without express permission of Honeywell.
Figure 7- -24
VNAV Path Descent Profile
A28- - 1146- - 181
REV 3 Mar 2009
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