Flight Management System Flashcards
The left and right GPS positions are displayed on POS REF page 3/3.
When the FMC is using GPS to update its position, it will be
displayed on the ND.
Should the ADIRU fail during flight, an EICAS caution message NAV ADIRU INERTIAL will be displayed along with the master CAUTION light.
In this situation, the FMC will now use
GPS only for navigation.
The Air Data Inertial Reference System (ADIRS) calculates airplane
altitude, airspeed, attitude, heading and position information.
The ADIRS supplies information to the display units,
Flight Management System,
flight controls, and engine controls.

The ADIRU is a fault-tolerant and fully redundant system supplying
the primary flight data, inertial navigation and air data.
Battery bus power is required during ADIRU initial power-up.
Before moving the airplane, a full alignment must be completed.
If electrical power is inadvertently removed from the airplane and the
BATTERY switch has been selected OFF, the ADIRU will still receive power
from
the hot battery bus.
The ON BAT light will illuminate.
Maintenance personnel will be alerted to this situation by the sounding of a
horn, located in the nose wheel well.
If the ADIRU is accidentally turned OFF in flight, system logic prevents the ADIRU from becoming unpowered.
If the ADIRU switch is turned OFF on the ground, it will
remain powered for a few seconds.
The scratchpad message INERTIAL / ORIGIN DISAGREE will display if the latitude / longitude position is not within
6 nm of the origin airport.
If an incorrect latitude / longitude is entered by the crew and the airplane senses
a disagreement to where it thinks it should be, the scratchpad message
ENTER INERTIAL POSITION will display.
The scratchpad message ALIGNMENT REINITIATED will display if a new present position entry fails twice.
This causes
a new alignment cycle to begin.
If the GPS position differs greatly from the entered ADIRU position, the scratchpad message NAV UNABLE RNP will display.
This is a rare occurrence and will rectify itself when the FMC reconciles the difference between the new
ADIRU position and the GPS position.
Each time the airplane is stopped for an extended period of time, the ADIRU will enter an automatic realign mode.
Position alignment will be refined until
the airplane starts to move again.
The ADIRU velocity and acceleration errors will be set to zero.
With the ADIRU in the automatic realign mode, a manual position update can be accomplished.
A new position can be entered on
POS INIT page 1/3.
NOTE: An ADIRU alignment cannot be accomplished in flight.
If the time between alignments is expected to exceed 24 hr, a position update is recommended.
When a ADIRU fault occurs, the SAARU will supply attitude data and will supply backup heading data for
3 min.
The heading is based on ADIRU heading prior to the failure.
After 3 min, heading data will be removed and a SET HDG prompt will be
displayed on the CDU POS INIT page.
The ADIRU and SAARU receive their air data from
the left, center and right pitot and static systems.
Two of these three air data sources must be in agreement before the ADIRU and
SAARU use the data.
There are 2 ADF systems installed on the airplane. Each ADF can be manually
tuned from
the NAV RADIO page on either CDU.
In the event of a dual FMC failure, the ADFs can be tuned using
the CDU ALTN NAV RADIO page.
There are 2 DME systems installed on the airplane. The DMEs, usually
autotuned by the FMC, may also
be tuned manually.
When the VOR portion of a VOR / DME is manually entered on the NAV RADIO page, the DMEs are considered to be tuned manually.
This does not inhibit FMC DME tuning.
Two DMEs are used by the FMC for position updates.
The FMC will tune DMEs as necessary for radio position updates.
This is seen on
POS REF page 2/3 displays the identifiers of the DME stations used for FMC position updates.
The DME / DME updates are usually more accurate than VOR / DME updates.
If the NAVAIDS have been inhibited on the REF NAV DATA page, the FMC
will be unable to tune specific DMEs.
In the event of a dual FMC failure, the VORs can be tuned manually using
the CDU ALTN NAV RADIO page.
Each DME tuned will be displayed on its own CDU.
NOTE: The only exception is if the ND mode selector is set to APP, the DME displayed will be that of the ILS.
The B777 has three ILS receivers which are usually tuned by the FMC.
They may also be manually tuned on the NAV RADIO page.
For ILS autotuning to occur, two conditions must be met.
he two conditions are: An ILS, LOC, back course, LDA (Localizer-type Directional Aid), or SDF (Simplified Directional Facility) approach must have been selected to the active route;
and the airplane must be within 50 nm from the Top of Descent, 150 nm of the landing runway threshold, or the FMC operating in descent mode.
To prevent clutter on the PFD, ILS autotuning is inhibited for
10 min after take-off.
This inhibit does not apply if a new approach is inserted into the active Flight Plan causing the ILS to autotune to the new approach frequency;
or
to subsequent take-offs and landings on the same flight (for example, touch-and-go or stop-and-go landings).
Unless ILS approach tuning inhibit is active, the three ILS receivers can be manually tuned from
the NAV RADIO page.









