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4. C. (4) (d) Descent
To descend, the pilot may select flight level change mode.
When FLCH is selected, the autothrottle smoothly reduces the
throttle setting to a minimum thrust
level to allow the
aircraft to achieve a reasonable rate of descent. The AFCS
controls airspeed through the elevator, as in FLCH climb.
Other potential flight guidance modes for descent include
vertical speed and pitch hold. Also, a VNAV path mode is
available for descent where the FMS coordinates with the AFCS
to maintain a programmed path angle. The autothrottle controls
airspeed (within engine limits) in all three of these descent
modes.
(e) Approach
During an instrument landing system (ILS) approach, the AFCS
works with the FMS to track the localizer and glideslope, while
the autothrottle controls airspeed. If the speed selector is
in the automatic (FMS) mode, speed targets are supplied by the
PZ-800 Performance Computer. As the aircraft nears the
destination, the speed target is automatically set to 10 knots
below the limit for 10 degrees of flaps. When the pilot
selects the 10-degree flap position, the speed target is set to
allow 20 degrees of flaps.
As the approach progresses, the
speed target is reduced until it is set to Vref + 10 knots for
final approach. The autothrottle is designed to accurately
control airspeed without excessive throttle activity or
sensitivity to turbulent conditions. The Gulfstream IV
autothrottle was certified for category II weather minimums.
(f) Go-Around
When engaged in any mode, autothrottle go-around can be
initiated by a single push of the takeoff/go-around button.
The autothrottle provides an automatic thrust increase to the
internally-computedmaximum engine rating. Go-around mode is
discontinued when another flight guidance mode is selected by
the pilot.
The AFCS disengages when go-around is initiated and
the flight director provides command bars on the primary flight
display.
22-14-00
Page 298.183
Aug 15/91
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