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A/T SYSTEM - FUNCTIONAL DESCRIPTION - ENGAGE LOGIC
A/T SYSTEM - FUNCTIONAL DESCRIPTION - ENGAGE LOGIC
EFFECTIVITY
SHZ ALL 22-31-00
Page 43
D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-31-00-014
General
The A/T computer receives digital and analog data from
different systems and sensors to determine operational modes.
This data comes into the A/T computer through the input
devices.
The A/T has two primary modes of operation, speed control and
N1 control. These are the only two A/T modes that are
selectable on the MCP. Depending on the flight phase and
mode selected, the A/T can enter these additional modes:
* Arm
* Retard
* Throttle hold
* Go-around
* Test (on the ground).
After the A/T enters a mode, it puts mode selection data on the
general ARINC output bus. These systems use the mode
selection data:
* DEUs to show A/T modes
* FDAU for data download and storage to the FDR
* FCCs for A/T mode status.
The A/T controls power to the ASMs. The A/T removes power
from the ASMs during throttle hold mode operation during
takeoff.
This section discusses each A/T mode of operation.
N1 Mode
The N1 mode is used during these flight phases:
* Takeoff
* Climb
* Maximum thrust go-around.
In N1 mode, the A/T controls thrust to the EEC TRA target,
calculated by the EEC for the equivalent FMC N1 target. The N1
mode can be selected in these four ways:
* Pilot manually selects N1 mode from the MCP
* DFCS requests N1 mode when DFCS is engaged
* TO/GA switch is pushed for takeoff (on ground)
* TO/GA switch is pushed a second time during reduced thrust
go-around (in the air).
When DFCS is engaged in VNAV climb or LVL CHG climb, the
FCCs command the A/T to N1 mode. When the DFCS is not
engaged, the pilot can push the N1 selector switch on the MCP
to manually select the N1 mode.
A/T SYSTEM - FUNCTIONAL DESCRIPTION - MODE SELECTION
EFFECTIVITY
SHZ ALL 22-31-00
Page 44
D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-31-00-015
Throttle Hold Mode
The throttle hold mode is automatic and the A/T goes into this
mode during the takeoff ground roll. In this mode, the A/T
removes power to the ASMs to prevent the A/T from moving the
T/Ls during the takeoff roll and initial climbout. The A/T uses
two separate functions to remove power from the ASMs. One is
a software function and the other is a hardware function. When
both throttle hold functions agree and remove power to the
servos, the A/T mode shows THR HLD on the FMA.
Arm Mode
ARM mode means that no active A/T mode has been selected.
In the ARM mode, the A/T is enabled and ready to receive
commands. The ASMs are powered but the A/T control logic
prevents the servo motors from moving the throttles. The A/T
goes to ARM mode during these conditions:
* On the ground when A/T is armed during preflight
* After THR HOLD mode above 800 feet barometric alt
* During Descent RETARD when T/Ls reach aft stops.
Speed Mode
In the speed mode, the A/T controls engine thrust to control
airplane speed. It does this by comparing the actual computed
airspeed (CAS) from the ADIRU, to the target speed from the
MCP. These are the two A/T Speed modes:
* FMC SPD from the FMC target speed
* MCP SPD from the speed selected on the MCP.
In FMC SPD mode, the A/T controls thrust to control airplane
speed to the FMC flight plan target speed. When the A/T is in
MCP SPD mode, it controls thrust to control airplane speed to
the target speed selected on the MCP.
The A/T Speed mode can be selected automatically or
manually. If the DFCS is engaged, the DFCS selects the A/T
speed mode automatically, either FMC SPD or MCP SPD,
consistent with the active DFCS pitch mode. A/T MCP SPD
mode may also be selected manually by a push of the A/T
speed mode selector switch on the MCP.
Retard Mode
In the RETARD mode, the A/T moves the T/Ls to the aft stops.
These are the two retard modes.
* Descent RETARD
* Flare RETARD.
Descent RETARD occurs during descent from altitude. Flare
RETARD occurs during flare to landing. Both modes show as
RETARD on the FMA on CDS.
A/T SYSTEM - FUNCTIONAL DESCRIPTION - MODE SELECTION
EFFECTIVITY
SHZ ALL 22-31-00
Page 45
D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
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