787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Flight Management, Navigation -
Navigation Systems Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 11.20.3
Air Data Reference System (ADRS)
The ADRS provides airplane altitude and airspeed for the displays, flight
management system, flight controls, engine controls, and other systems.
Air Data and Attitude Sources
The ADRS receives air data from the left, center, and right pitot and static systems,
and sends trusted voted air data to the PFDs. The ADRS is completely
independent of the IRS.
When voted ADRS air data is invalid and the AIR DATA/ATT switch is in the
AUTO position, backup airspeed (AOA SPD) and/or backup altitude (GPS ALT)
are automatically provided by the IRS and GPS systems. (Refer to Instrument
Source Select Panels in Chapter 10, Section 10, for additional information.)
The air data modules are remote sensors that convert the sensed analog pressures
to digital values for the air data functions within the ADRS. In addition, the ADRS
receives data from two angle of attack vanes, an airframe mounted dual element
total air temperature probe, and engine TAT sensors.
The integrated standby flight display (ISFD) receives data from the center pitot
static system. Altitude, attitude, and airspeed are independent of IRU and AHRU
values.
In the event both voted and backup air data is unavailable, ISFD altitude (ISFD
ALT) and ISFD airspeed (ISFD SPD) are displayed on the PFDs.
Inertial System
Inertial Reference System (IRS)
The IRS calculates airplane altitude, airspeed, attitude, heading, and position data
for the displays, flight management system, flight controls, engine controls, and
other systems. The major components of IRS are the inertial reference units
(IRUs), and attitude and heading reference units (AHRUs).
Inertial Reference Unit (IRU)
The IRU combines inertial reference functions with GPS position information to
provide hybrid GPS-inertial position outputs.
IRU Power
Initial power–up requires battery bus power and the IRS switches to be ON. If the
IRSs are switched off, they must complete a full realignment cycle before the
airplane can be moved.
August 14, 2009
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