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trim. This lesson describing system operation is intended to help
maintenance personnel understand DFCS operation. The DFCS
operation is divided into two parts: normal operation and supplemental
normal operations. The normal operation includes a typical normal
flight from takeoff to landing. The supplemental normal operation
includes pitch control and roll control by using CWS (control wheel
steering), approach by using a single A/P, and go-around by using F/D
only.
[2] Figure 38-1 shows the component location of DFCS. The DFCS
mode control panel (MCP) is located on the glareshield (P7). An
autoflight status annunciator is located on each pilot's panel (P1, P3).
An EADI is located on each pilot's panel (P1 and P3). The flight mode
annunciator (FMA) function is contained on EADI. The takeoff
go-around switches and autothrottle disconnect switches are located on
the thrust levers. An autopilot disconnect switch is located on the
outboard side of each pilots control wheel. A yaw damper ON/OFF
switch is located on the flight control module.
Figure 38-1 DFCS Component Locations
Three caution annunciators are located on the flight control module on
the overhead panel. These annunciators are SPEED TRIM fail and YAW
DAMPER fail. A single STAB out of trim annunciator is located on the
captain's panel. An altitude warning annunciator is located on each
pilot's panel. The aural warning signal, generated from the FCC, is sent
to the Audio Distribution System. A thrust mode annunciator is located
on the center instrument panel (P2).
[3] Figure 38-2 illustrates the DFCS mode control panel (MCP). The
MCP provides the primary interface between the pilots and the DFCS.
The MCP contains engagement control, mode selection control and
parameters selection control.
1. Engagement control
Two A/P engage switches are solenoid-held in OFF, CWS, and
CMD positions. If proper logic is made, the solenoid releases the
switch allowing movement from the OFF position. If engage logic is
satisfied, then the switch will hold in CWS or CMD position. The A/T
ARM switch is a solenoid-held switch for arming the autothrottle. On
the ground the FMCS must be engaged in TO before the autothrottle can
be armed. Two flight director ON/OFF switches provides control of the
flight director command output to the EADI.
2. Mode selection control
Mode selection is made with momentary pushbuttons. The
pushbutton modes are HDG SEL, VOR/LOC, APP, LNAV, VNAV, ALT
HOLD, V/S, LVL CHG, (A/T)SPEED, and (A/T) N1. CWS mode is
the only A/P mode available with engage switch in CWS. In CMD
position, CWS is the applicable mode when a pushbutton mode is not
selected. When on the selected altitude and in altitude hold the ALT
HOLD light is off indicating that ALT HOLD cannot be de-selected
using the ALT HOLD PB switch.
3. Parameters selection control
The knobs on the MCP are used for selection of IAS/MACH,
altitude, heading and courses. These knobs are connected to encoders
whose output signals drives the displays. V/S selection is accomplished
by a wheel rather than a knob. The V/S selects vertical speeds between
-7900 and +6000 feet per minute. The vertical speed control wheel
provides increments of 50 feet per minute from 0 to 1000 feet and 100
feet per minute above 1000 feet. The altitude knob changes the selected
altitude in 100 feet increments. One complete rotation of knob changes
the altitude by 6400 feet. The selectable range is between 0 and
+50,000
Fig. 38-2 DFCS Mode Control Panel
feet. IAS/MACH selection is from 110 to 340 and 0.6 to 0.82 in
increments of 1kt or 0.01 M. IAS/MACH display is limited to the
existing VMO/MMO. The bank angle selector permits selection of
maximum bank angle (10 to 30 degrees) in increments of 5 degrees in
some roll modes. Liquid Crystal Displays provide a digital readout of
preset heading, IAS/MACH, altitude, vertical speed, and separate
captain's and first officer's preset course selections. Additionally, the
IAS/MACH LCD has flashing warning flags for underspeed and
overspeed in the left most position. Undersped (A) is displayed if the
airplane speed is decreased to the minimum speed except in TO or GA.
The A remains until the speed has been increased to 15 knots above the
minimum speed. Overspeed is displayed when the airplane speed is
greater than the VMO/MMO limit or speed is within 2 knots of the flap
or gear placard or while in VNAV mode in descent below 10,000 feet
and airspeed great than 255 knot.
[4] Figure 38-3 illustrates the autoflight status annunciator. This
annunciator indicates the fail/warn status of the A/P, A/T, and FMC. The
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