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.
11.20.4 D615Z003-TBC
If electrical power is subsequently removed from the airplane and the Battery
switch is switched OFF, the hot battery bus continues to supply electrical power
to the IRS. The ON BAT light illuminates, and the horn in the landing gear wheel
well sounds to alert maintenance personnel that the IRS is on battery power.
IRU Alignment
On initial power–up, the IRUs enter the align mode. The EICAS memo message
IRU ALIGN MODE L+R displays. Attitude or heading/track data is removed
from the PFDs. When the GPS system is operating normally there is no
requirement for the flight crew to enter present position on the CDU POS INIT
page. The POS INIT page displays dashes in the ENTER PRESENT POSITION
line to allow the option of manually entering present position. If the GPS position
is not available during the alignment, the dashes are replaced with boxes and
present position must be entered to complete the alignment. Alignment time is
approximately 7 to 10 minutes at mid latitudes and up to 17 minutes at high
latitudes. The airplane should not move until alignment is complete.
If the latitude/longitude position is not close to the position of the origin airport,
the EICAS advisory message FMC MESSAGE is displayed along with the CDU
help window message INERTIAL/ORIGIN DISAGREE. If the crew–entered
latitude/longitude position does not pass internal IRU comparison tests, the
EICAS advisory message FMC MESSAGE is displayed along with the CDU help
window message ENTER INERTIAL POSITION.
If a new airplane present position entry fails the internal check twice, the EICAS
advisory message FMC MESSAGE is displayed along with the CDU help
window message ALIGNMENT REINITIATED. The system automatically starts
a new alignment cycle.
When the alignment is complete, the IRS changes to the navigate mode and the
airplane can be moved. If the airplane stops for an extended period, the IRS
changes to the automatic realign mode and refines the alignment until the airplane
moves again.
In the automatic realign mode, IRS velocity and acceleration errors are reset to
zero. The inertial position can be manually updated when the IRS is in the
automatic realign mode by entering a new latitude/longitude position on the POS
INIT 1/3 page.
February 15, 2010
To Next Page
Loading...
