(a) The dot-bar matrix in the APP switch/light lights when the MCP receives APPROACH MODE ARM/OPER from the FCCs. Once the approach mode is engaged, it can be disabled when the following modes are selected: HDG HOLD, HDG SELECT, or LNAV.
(15)
The IAS/MACH display has four valid states.
(a)
OFF
(b)
Airspeed being displayed: Airspeed (IAS) display is entered automatically when MCP power is turned on or when the SPD knob is pressed. Airspeed is also displayed if the SEL switch is pressed when MACH is being displayed, or if the display is blank when SPD or FL CH modes are initiated. If the reference airspeed from the FCC is invalid, the display shows 200 knots.
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(c)
MACH being displayed: this state is entered if the SEL switch is pressed when airspeed is being displayed and the airplane's speed is between 0.400 and 0.950 Mach.
(d)
Speed display blank: this state is entered from either IAS or MACH display states if the VNAV mode is initiated or the SPD knob is pressed with the AFDS not in the FL CH, SPD, or T/O modes. (These are airspeed-being-displayed only modes.)
(16) The DISENGAGE bar provides total disengagement of all three FCCs. The switch assembly consists of three DPDT toggle switches (one for each FCC) tied together with a bar. When the bar is up, the servos may be engaged; when down, 28 Vdc is removed from the servos, preventing engagement. When the bar is down, a dayglow orange strip is visable, annunciating the disengaged position of the switch.
4. Airplane Sensors and Interfacing Components (Figure 3)___________________________________________
A. Critical sensors are those which provide raw data inputs during Autoland. Each FCC receives a dedicated input from a critical sensor. Autoland critical sensors are the Instrument Landing System (ILS) receiver, Inertial Reference Unit (IRU), Radio Altimeter (RA), Bus Control Unit (BCU), Speed Brake RVDT, and the Flap Control Unit (FCU).
B. Non-critical sensors are those which do not provide essential raw data during autoland. The FCCs receive non-critical sensor inputs through instrument switching or common data links. Non-critical sensors are the Flight Management Computer System (FMCS), Air Data System (ADS), and the Proximity Switch Electronic Unit (PSEU).
C. The following is a list of the airplane sensors and interfacing
components and the type of information each provides.
(1) MCP digital inputs to FCC
Mode status
Mode request
Altitude selected
Heading selected
Mach selected
MCP maintenance data
Airspeed selected
Test word
Vertical speed command
Vertical speed selected
FMC airspeed reference Mach
Selected runway heading
Speed brake handle position
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(2)
FCC digital inputs to MCP Mode status Computed airspeed Elevator speed command Flap position FMC airspeed reference Mach Selected runway heading Speed brake handle position Stabilizer position Test word Vertical speed
(3)
Control wheel analog discrete to FCC A/P disengage
(4)
Control aisle stand analog discrete to FCC Go-Around
(5)
ILS digital inputs to FCC Glideslope deviation Localizer deviation ILS frequency Selected runway heading
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