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Flight Management System (FMS) for the Agusta AW139/AB139 Helicopter
APPROACH TO FHAF
After engaging the MOT, the FMS creates and activates a MOT flight
plan. The FMS does not command a climb throughout the MOT
maneuver. Vertically, the FMS constructs a 3 degree descent path from
the HOV waypoint passing through the FHAF and continuing upwards,
as shown in Figure 6--126. The aircraft crosses the FHAF at 250 ft AGL.
Laterally, the FMS computes the optimum lateral trajectory into the
FHAF to minimize the amount of time required to perform the return
maneuver. During the Approach to FHAF phase, the flight director uses
the following FMS control data:
Lateral -- FMS provides lateral guidance by LNAV roll steering
D
commands.
Vertical -- When the aircraft is below the 3 degree descent path and
D
the MOT is initiated, the AFCS and FMS remain in altitude hold
(VALT) and the AFCS flies a radio altitude hold (VRHT) until
intersecting the 3 degree descent path. Prior to intersecting the
3 degree descent path, the FMS and AFCS remain in VALT. After
intersecting the 3 degree descent path, the FMS provides vertical
guidance by way of the vertical speed (VS) commands.
When the aircraft is above the descent path and the MOT is initiated,
the FMS commands a direct--to descent (VNAV) to the FHAF. The
maximum angle for the VNAV to the FHAF is 4 degrees and is
displayed the same way as other VNAV descents are displayed.
Speed -- Speed guidance is by way of the FMS CAS target. The
D
FMS CAS target is initially set to a value of 60 kts plus the wind
speed when current speed is greater than this value. When the
current speed is less than this value, the speed command is set to
the current speed (to avoid speeding up and slowing down later). As
the helicopter is approaching the FHAF, the FMS speed command
is reduced at an appropriate location in the flight plan so the GS at
the FHAF is 60 kts.
After engaging the MOT, the AFCS controls the approach to the FHAF
as follows:
Collective beep sets RHT height
D
Collective FTR does nothing
D
Cyclic beep does nothing
D
Cyclic FTR does nothing.
D
A28- - 1146- - 181
REV 3 Mar 2009
Honeywell International Inc. Do not copy without express permission of Honeywell.
Navigation
6-165
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