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the FMC light on the autoflight status annunciators when the
FMC fails or when there is a message that makes flight crew
awareness and subsequent action necessary.
FMCS - FMC FUNCTIONAL DESCRIPTION - INTRODUCTION
EFFECTIVITY
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FMCS - FMC FUNCTIONAL DESCRIPTION - INTRODUCTION
FMCS - FMC FUNCTIONAL DESCRIPTION - INTRODUCTION
EFFECTIVITY
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General
The FMCS navigation sub-function calculates this data:
* Lateral position
* Vertical position
* Actual navigation performance (ANP).
The primary data source for the lateral and vertical position
calculations is the ADIRU. Because the ADIRU data drifts over
time, the FMC navigation function uses data from other sensors
to correct the ADIRU data that it receives.
The FMC uses independent measurements from the navigation
sensors filtered with ADIRU position, heading and velocity data
to produce an accurate calculation of the airplane’s position in
the horizontal plane.
NOTE: The ADIRU must be in the NAV mode to provide valid
data to the FMC.
The FMC will select only one navigation update mode at a time.
The navigation update mode with the least amount of position
uncertainty will be used.
These are the sensors used to calculate/update the FMC
position and their selection priority:
* ADIRU/GPS
* ADIRU/DME/DME
* ADIRU/DME/VOR
* ADIRU/DME/LOC
* ADIRU ONLY.
The first priority for FMC position updating is GPS data from the
GPS receiver in the MMRs.
The next priority is a pair of DME stations that have the best
range and geometry. The maximum range for DME/DME
updating is nominally 200 nautical miles (NM) but the FMC
will always use those stations that are nearest the airplane
position. The FMC will also always tune two DMEs that are not
within 30 degrees of each other or not greater than 150 degrees
apart (90 degrees being the optimum angle).
If there are not two DME stations within range or that do not
have the necessary geometry, the FMC uses DME distance and
VOR bearing from a co-located VOR/DME station. The
maximum range for VOR/DME update is 25 nautical miles.
NOTE: The FMC will autotune the DME interrogators but VOR
must be manually tuned by the flight crew.
In an airport terminal area when the airplane is on a localizer
approach, the FMC uses localizer deviation and DME distance
to update the FMC position. The maximum range for LOC/DME
update is 20 nautical miles and the airplane altitude must not be
greater than 6000 feet above the localizer station elevation.
Also, the airplane track must be within 45 degrees of the
localizer inbound course and localizer deviation must be less
than 1.25 dots for at least 5 seconds.
FMCS - FMC FUNCTIONAL DESCRIPTION - NAVIGATION SUB-FUNCTION
EFFECTIVITY
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With all VHF NAV radio updates, the FMC will correct the DME
slant range distance for airplane altitude.
If GPS data and NAV radio data are not available or become
invalid, the FMC uses ADIRU data only corrected by a fixed
error bias calculated by the FMC.
The FMCS can use GPS data on the ground to update the FMC
position if the GPS data is valid. VHF NAV radio update is not
enabled on the ground.
The navigation sub-function also calculates the following nav
data:
* Airplane position (latitude, longitude and altitude)
* Groundspeed
* Flight path angle
* Drift angle
* Track angle
* Wind velocity and direction
* Horizontal position accuracy (actual navigation
performance).
The FMC uses the following inputs to calculate these
parameters:
* Inertial position (latitude, longitude and inertially smoothed
altitude)
* Vertical speed (inertially smoothed)
* Groundspeed components (N-S, E-W velocity vectors)
* Heading (magnetic and true)
* Pressure altitude (uncorrected and baro-corrected)
* True airspeed
* GPS data
* DME slant range
* VOR bearing
* ILS LOC deviation.
Lateral Position
This function calculates latitude and longitude.
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