FLIGHT GUIDANCE CONTROL SYSTEM.
The MD-80 digital flight guidance system is a dual, autopilot, flight director
and autothrottle system with fail passive autoland capability. It is designed for
guidance throughout the full flight regimes, from takeoff through climb, cruise,
descent and landing included the roll-out.
Two fully independent Digital Flight Guidance Computers (DFGC) perform the
necessary calculations based on inputs from various sensors, and provide outputs
to drive the flight director command bars in the two Primary Flight Displays (PFD).
When the autopilot is engaged, one of the two DFGC (pilot selectable) provides
command signals to the duplex servo actuators controlling roll, pitch, yaw and
pitch-trim surfaces. The DFGC, not in use receives and processes the same input in
parallel and acts as a hot spare, ready to take over by pilot command, if the DFGC
in use should fail.
When autothrottle is engaged, the selected DFGC provides commands to the
duplex throttle servo controlling the power levers.
FLIGHT GUIDANCE CONTROL PANEL FGCP.
The flight guidance system is controlled from a glare shield mounted control
panel. The FGCP serves as the control center for the flight guidance system. On
the FGCP are controls for selection of Flight Director/Autopilot operational
modes and Autothrottle operational modes located. Autopilot engage and DFGC 1/2
selector switches as well as switches for removal of the flight director command
bares from the PFD are also part of the FGCP.
FGCP speed.
- Flight director switch.
- FD - Engages the left pilot flight director. Flight director steering
commands are displayed by the crossbars on the left pilot PFD.
- OFF - The flight director is off and the crossbars will be removed from
the PFD.
- FMS OVRD
- Engages the FMS override mode in which the FMS target speed can be
modified through the use of the SPD/MACH select knob while the DFGS remains
under FMS VNAV control.
- SPD SEL autothrottle mode button.
- Engages speed select mode. The autothrottle will control engine thrust
to achieve and maintain the selected IAS.
- MACH SEL autothrottle mode button.
- Engages Mach select mode. The autothrottle will control engine thrust to
achieve and maintain the selected Mach No.
- EPR LIM autothrottle mode button.
- Engages EPR limit mode. The autothrottle will control engine thrust to
achieve and maintain the thrust rating selected on the TRP (Thrust Rating
Panel).
- Autothrottle SPD/MACH readout.
- Digital readout of preselected IAS or Mach number. If VNAV button is pressed,
FMS target speed will be displayed in IAS regardless of altitude.
- Autothrottle SPD/MACH select knob.
- The knob has three push positions spring loaded to normal.
- Normal position selects IAS/Mach at a low rate of change.
- Pressing to the mid position increases the turn rate of change.
- Pressing fully in alternatively changes between SPD and Mach and stores
data in DFGC.
- AOTO THROT (AT) switch.
- Engages the autothrottle.
FGCP lateral and vertical navigation.
The two white knobs, below the Pitch Control Wheel adjusts the intensity of
the mode buttons and the edge lightning.
- NAV mode button (roll mode).
- Arms the FGS to capture and track a course given by the Flight Management
System.
- VOR LOC mode button (roll mode).
- Arms the FGS to capture and track a selected VOR or Localizer beam. FD
roll command bar will display roll commands and the autopilot will fly the
aircraft to capture and track the selected beam.
- ILS mode button.
- Arms the FGS to capture and track a selected localizer course and glideslope.
FD command bars will display roll and pitch commands and AP will fly the aircraft
to capture and track localizer and glideslope.
- AUTOLAND mode button.
- Arms the autopilot to engage autoland mode after localizer and glideslope
capture. After both localizer and glideslope are being tracked and AUT LND is
annunciated in both the roll and pitch displays of the TARP, all other control
modes are inhibited (except go-around).
- Heading (HDG) select knob. A four position push/pull knob spring
loaded to normal position.
- Normal position provides fine heading select.
- Pushing to first detent provides fast heading select.
- Pushing fully in cancels any armed roll mode, engages heading hold mode
and the aircraft will hold existing heading.
- Pulling the knob engages the heading select mode.
- In either mode the FD roll command bar will display commands and the autopilot
will fly the aircraft to maintain the heading.
- Bank angle selector. Inside the black HDG knob.
- The knob selects the maximum bank angle. It has five detents from 10°
to 30° and limits the bank angle in all modes except VOR TRK, LOC and NAV.
- HEADING readout. Above HDG knob.
- Digital readout of selected heading.
- Pitch control wheel (PCW).
- Permits control of vertical speed, IAS/Mach or pitch attitude depending
on engaged pitch mode.
- Manually rotating the PCW toward AND (Aircraft Nose Down) or ANU (Aircraft
Nose Up) will cause pitch profile readout display to change. When in FD, the
pitch bar in the PFD will indicate pitch commands. When autopilot is engaged,
the aircraft will maneuver to maintain the pitch reference set by the PCW.
Rotating the PCW to center detent (less than 100 ft/min) will engage the altitude
hold mode.
- When operating in IAS or Mach hold mode, the IAS or Mach reference value
can be adjusted by use of the PCW. The new reference value together with S or
M will be displayed in pitch profile readout.
- When in turbulence mode, the pitch attitude can be adjusted by use of the
PCW. The new value will be displayed on the pitch profile readout.
- Pitch profile readout. Above the PCW.
- The first window displays the operating mode:
- Vor vertical speed.
- M for Mach.
- S for IAS.
- Por turbulence (Pitch).
- The second window displays pitch reference:
- Plus (+) for climb
- Minus (-) for descent.
- The remaining windows display appropriate numerical values.
- VERT SPD mode button.
- Selects vertical speed mode. Vertical speed can be adjusted by the PCW.
FD pitch command bar displays pitch commands to maintain selected vertical speed
and autopilot, if engaged, will maintain selected vertical speed by pitch control.
- IAS MACH mode button.
- Above 27 000 ft selects existing Mach number, can be adjusted by the PCW.
If desired, the IAS mode can be selected by pressing the button a second time.
- Below 27 000 ft selects existing airspeed for IAS control mode. If desired
Mach mode can be selected by pressing the button a second time.
- FD pitch command bar displays pitch commands to maintain selected Mach or IAS.
Autopilot, if engaged, will adjust pitch attitude to maintain selected Mach or IAS.
- VNAV mode button.
- Selects FMS data for FD or autopilot pitch control and autothrottle
thrust control.
FGCP altitude preselect..
- ALT HOLD mode button.
- Selects existing altitude for flight guidance system altitude hold mode.
FD pitch command displays pitch commands to maintain altitude and the autopilot
will hold existing altitude by pitch control.
- AP ON switch.
- Engages the autopilot.
- 1-2 switch.
- Selects flight guidance computer No. 1 or 2 to perform all DFGS functions.
- Altitude preselect readout.
- Digital readout of preselected altitude in the range 000 to 50 000 ft.
- ALT set knob.
- Approximately one second after a new altitude is selected, the FGS automatically
arms for capture of the preselected altitude.
- The knob has three push-pull positions, spring-loaded to center.
- In center position, turning the knob provides altitude adjustments in
1 000 ft increments.
- In the pushed position, turning the knob provides altitude adjustments in
100 ft increments.
- Pulling the knob provides instant arming for capture of preselected altitude.
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