IRS - Inertial Reference System *** Flashcards
How do you select the IRU mode selector from NAV?
• The selector must be pulled out
What is the function of the ALIGN position of the IRU Mode Selector?
- Initiates alignment
* Removes sensor errors when selected from NAV mode
How long does it take for full alignment of the IRS?
• aprox 10 minutes because is depend of the latitude of the present position
When is full alignment of the IRS required?
• When the time from the last full alignment to the next expected arrival time exceeds 18 hours.
How do you accomplish a fast alignment of the IRS?
• Airplane must be parked • Position the selectors to ALIGN • Enter present position • Reposition the selectors to NAV • Takes 30 seconds • Fast alignment can be accomplished without entering a present position. However, greater navigational accuracy is attained by entering present position
What does the IRS ON Battery (BAT) Light mean, when displayed on the Overhead Maintenance Panel?
• IRS operating on backup electrical power (APU hot battery bus)
Explain what happens when the alignment of the IRS is lost in flight.
- The navigation mode is inoperative for the remainder of the flight.
- Attitude information can be obtained by moving the selector to ATT.
What happens if the center IRU is operating on DC power?
• The center IRU operates on DC power for 5 minutes, then shuts down.
What are the sources of power for the IRSs?
AC power 1,2,3 – Primary, DC power (APU Hot Battery Bus) Backup
How are the IRSs affected in the event of loss of Main AC power?
They revert to DC backup power (via the APU hot battery bus) Center only runs for 5 minutes.
Horn will sound on the landing gear
What are 4 indications on the PFD that are from the IRU
Attitude
Heading
V/S
Green A/S trend Arrow
What bus is the IRU on?
AC 3 - L
AC 1 - C
AC 2 - R
IRS position update priority
Where can it be found
LOC and GPS Loc and DME-DME Loc and colocated VOR/DME LOC GPS DME-DME Colocated VOR/DME
Fcom 2 11.31.8
The FMC changes to LOC updating when
the airplane is less than 6,000’ above the localizer navaid elevation
the airplane is less than 20nm from the front course
or 12nm back course
Can IRS fast alignment be accomplished without entering the present position?
YES, but greater nav accuracy is attained by doing so.
