(2)
When automatic tuning is selected, station selection is determined by the FMC, using navigation information and station geometry information. In the event that one of the DME interrogators is manually tuned to a station that does not satisfy the range and geometry of the FMC, (or if one of the DME interrogators fail); the FMC will automatically place the remaining DME interrogator in a frequency agility mode, provided automatic tuning has been selected. This remaining DME interrogator will be automatically tuned, (at five-second intervals), between two DME stations. Two DME stations, however, must be available that satisfy the range and geometry criteria of the FMC. Agility tuning allows DME/DME position determination with a single DME.
E. VHF Navigation Receivers
(1) The VHF navigation receivers provide deviation and bearing information to the FMC, through the DAA. When manual tuning is selected on the VHF navigation control panel, a manually selected VHF frequency is tuned. If automatic tuning is selected, the VHF navigation receivers are tuned by signals from the FMC, and station selection is determined by the FMC, using navigation and station geometry information.
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Fuel Quantity
(1)
The fuel summation unit processes and sums signals from individual fuel tank indicators, to determine total fuel. The summation unit provides this total fuel information to the FMC, through the DAA.
Inertial Reference System (IRS)
(1)
The IRS is the primary component on the airplane for attitude measurement, and position determining. The IRS utilizes a ring laser as its means of inertial reference. Each IRS provides present position, heading, attitude, velocity, altitude, ground speed, and vertical speed to the FMC; through an ARINC 429 high-speed Digital Information Transfer System (DITS).
(2)
An output ARINC 429 channel from the FMS allows the user to initialize the IRS on the ground through the CDU by entering the airplane present position latitude and longitude values.
Digital Air Data Computer System (DADC)
(1)
Two DADC interface with the FMC. The DADC system provides altitude, DADC, airspeed, mach, and temperature information to the FMC, through an ARINC 429 low-speed DITS.
Captain's Clock
(1)
The clock provides an output of Greenwich Mean Time (GMT), or GMT and date (if GMT and date clock is installed) to the FMC. This interface is in accordance with ARINC 429 low-speed DITS.
Discrete Signals
(1)
The FMC accepts discrete input signals from wing anti-ice, engine anti-ice, and engine bleed systems. These systems when activated cause an engine thrust reduction. The FMC uses these discrete signals to provide corresponding reductions to calculated performance values.
Autothrottle Computer (A/T)
(1)
An output of the FMC interfaces with the autothrottle computer (A/T), through an ARINC 429 low-speed DITS. This output from the FMC provides the A/T with climb, cruise, and go-around N1 limits. The output also provides the A/T with gross weight and temperature data.
Digital Flight Control System (DFCS)
(1)
The DFCS Mode Control Panel (MCP) provides LNAV and VNAV engage mode logic, altitude select data, and flap position to the FMC, through an ARINC 429 low-speed DITS.
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(2) An output of the FMC interfaces with the DFCS Flight Control Computer (FCC), through an ARINC low-speed DITS. This output from the FMC provides the FCC with target airspeed and mach, target altitude, target vertical speed, and roll command.
M. Horizontal Situation Indicator (HSI)
(1) The FMC provides FMC computed navigation data to the HSI through the DAA. Pilots flight instrument switches allow the HSI to display either FMC computed navigation data, or navigation data from radio navigation systems. The IRS provides heading information to the HSI azimuth card.
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