NAVIGATION AND
COMMUNICATION
AIRPLANE
OPERATIONS
MANUAL
2-18-35
Page
4
Code
01
REVISION 28
FMS OPERATING MODES
FMS FUNCTIONS
NAVIGATION
The navigation function computes the airplane position and velocity for
all phases of flight. The navigation priority modes, based on sensor
accuracy, are as follows:
− GPS
− DME/DME
− VOR/DME
− IRS (if installed)
The GPS is the most accurate sensor. When the GPS is in use, the
other sensors are still monitored for position differences, but they do
not contribute to FMS position, unless the GPS becomes inaccurate,
unavailable or is manually deselected. In this case, the FMS
automatically tunes the DME/DME in order to provide position. When
DME/DME is not accurate, the VOR/DME is selected.
On airplanes equipped with dual Inertial Reference System (IRS),
replacing the AHRS, the IRS is used as a primary navigation sensor
when other navaid are not available.
If all position sensors and radios are lost, the FMS shifts to Degrade
Mode (DGRAD) and in approximately 2 minutes it enters the Dead
Reckoning Mode (DR). In this mode, the position is calculated using
the last known airplane position. The ground speed and track are
estimated with AHRS/IRS heading, ADC TAS and the last known wind
data.
The dual FMS configuration (NZ5.2 software version and on) may
operate with dual IRS and dual GPS providing four long-range
navigation sensors. The sensors status may be accessed in the NAV
INDEX 1/2 page.
In this configuration, on-side FMS outputs and flight plan information
are available to the opposite-side FMS through an interconnecting bus.
The automatic tuning is made through the RMU for computing an
optimum position. The FMS also includes a radio-tuning page on which
the pilot can manually select VHF NAV, COM, ADF and transponder
frequencies. The NZ5.2 software version and on has the capability of
tuning communication frequencies in the 8.33 kHz channel spacing.
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