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Flight Management System (FMS) for the Agusta AW139/AB139 Helicopter
Speed Protection
The FMS gives two types of speed protection:
1. Automatic transition from VPATH to VFLCH (referred to as speed
reversion).
2. Latched speed.
During path descents, speed control is secondary to path control. When
the path descent is too steep, the aircraft increases speed even at idle
power and the message INCREASED DRAG REQUIRED is displayed.
When the aircraft speed continues to increase, the FMS transitions to
speed reversion function. In this function, the FMS transitions out of
VPATH to VFLCH to enable the FMS to pull off the path and give speed
protection.
The FMS automatically transitions from VPATH to VFLCH for the
following conditions:
V
/M
-- During a VPATH descent when CAS becomes greater
D
MO
MO
than V
+10 kts. The transition is canceled when the airspeed
MO
decreases to V
Speed/Altitude Limit -- During a VPATH descent with autothrottles
D
engaged, the FMS outputs an altitude target equal to the speed limit
altitude when the aircraft speed exceeds the speed constraint (for
example, 250 kts at 10,000 ft) by more than 5 kts. Under these
conditions, the FMS levels the aircraft at the speed limit altitude until
the aircraft speed is 2 kts greater than the speed limit. The FMS then
requests a VFLCH descent down to the altitude preselector.
When autothrottles are not engaged or the aircraft is not equipped with
autothrottles,
the FMS continues the descent
speed/altitude limit. The pilot is responsible for controlling the speed of
the aircraft to meet the speed/altitude limit.
Speed/altitude limit protection is also given during VFLCH descents.
Under these conditions, the FMS slows the aircraft to the speed limit
when approaching the altitude associated with the speed limit.
Landing Gear Or Flap Placard Speed -- During a VPATH descent,
D
the aircraft speed exceeds the landing gear or flap placard speed by
10 kts.
V
-- During a VPATH descent and the aircraft speed is less than
REF
D
V
by 10 kts.
REF
The second speed protection is latched speed mode. The latched
speed mode is entered when a significant difference is between the
actual aircraft speed and the speed command. When the latched speed
mode is entered, LATCHED at 1R is displayed, as shown in
Figure 7--32, on the ACTIVE FLT PLAN page.
Flight Plan
7-54
Honeywell International Inc. Do not copy without express permission of Honeywell.
+2 kts.
MO
through the
A28- - 1146- - 181
REV 3 Mar 2009
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