Honeywell SPZ-8000 Maintenance Manual page 636

4. C. (2) Autothrottle Function
(a)
Introduction
The functions which the autothrottle is capable of providing
vary depending on the phase of flight and operating modes of
other systems which interface with the autothrottle (i.e.,
navigation computer, flight guidance computer (FGC)). The
autothrottle has four basic modes of operation: takeoff,
go-around, flight level change (FLCH) mode, and speed hold.
When engaged and operating in the FLCH mode (FLCH mode is set
by the flight guidance computer) the autothrottle commands the
energy required by the flight guidance computer to accomplish
the FLCH climb or descent.
When engaged and operating in speed mode, the autothrottle
adjusts engine thrust via separate throttle servos (one servo
for each engine) to control aircraft speed to the target speed
which is displayed in the cockpit. The target speed may be
manually input or slaved to a speed determined by the
performance function depending on performance mode and pilot
selection.
Other autothrottle functions such as maximum operating speed
(VN~MO) protection, flap placard protection, extended landing
gear ~lmits, engine limit protection, and minimum thrust
control are performed in parallel with the basic modes.
The
autothrottle also provides engine low-rotor speed (%N1) or
high-rotor speed (%N2) synchronization in speed-hold mode as a
function of pilot selection.
The only valid bleed configurations for autothrottle operation
are: (1) cowl and wing anti-ice off, (2) cowl anti-ice on, (3)
cowl and wing anti-ice on. The environmental control system
(ECS) is assumed to be on and the isolation valve closed at all
times. If an invalid aircraft bleed configuration is sensed,
the autothrottle disconnects and an appropriate advisory
message is displayed. An appropriate delay is provided when
changing bleed configurations to prevent nuisance disconnects.
The autothrottle performance limits are listed in Table 208 and
the advisory messages which appear on the EICAS display are
listed in Table 209.
22-14-00
Page 298.174
Aug 15/91
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