IRS

Question 1

Function of ALIGN position of the IRU Mode Selector?

Answer 1

• Initiates IRS FAST alignment

- Removes sensor errors w/selected from NAV mode

Question 2

How long does full alignment of IRS take?

Answer 2

10 minutes

Question 3

When is full alignment of IRS required?

Answer 3

When time from last full alignment to the next expected arrival time exceeds 18 hours.

Question 4

How is IRS Fast Alignment accomplished?

Answer 4

• A/C Parked
• Selectors to ALIGN
• Enter present POS on POS INIT/SET IRS POS page
• Repositions selectors to NAV
• Alignment takes approx 30 seconds

Question 5

Can IRS fast alignment be accomplished without entering present position?

Answer 5

YES, but greater nav accuracy is attained by doing so.

Question 6

What does IRS ON BAT mean?

Answer 6

IRS operating on backup DC electrical power (APU HOT BUS)

*Center IRU will shutdown after 5 mins.

Question 7

What happens when align of IRS is lost in flight?

Answer 7

• NAV mode is inop for rest of flight.

- ATT information obtained by moving selector to ATT

Question 8

With regard to IRS, the primary mode of navigation is?

Answer 8

GPS Updating

Question 9

What is some of IRS calculated information?

Answer 9

• Position
• Accel
• Track
• VS
• T/M HDG
• Wind
• ATT
• GS

Question 10

IRS normally powered by?

Answer 10

AC PWR
L - AC 3
C - AC 1
R - AC 2

Question 11

IRS backup power source?

Answer 11

DC PWR via APU HOT BATTERY BUS

Question 12

IRS alignment determines A/C relationship to?

Answer 12

True North

Question 13

Why must A/C remain stationary for IRS alignment?

Answer 13

Ensures only motion detected is by Earth’s rotation

Question 14

How is the IRS alignment process accomplished on the ground?

Answer 14

IRS switches are moved from OFF to NAV and crew enters IRS POS in FMC.

Question 15

With regard to the IRS, what does it mean when FMC LAST POS changes to the new PRES POS on INIT PAGE?

Answer 15

The first IRU has entered navigation mode.

Question 16

How do you know if all 3 IRUs have entered navigation mode?

Answer 16

• SET IRS POS disappears in FMC
• Memo message disappears on EICAS
• Appearance of HDG and ATT info on PFD

Question 17

Most common reason to perform IRS fast realignment?

Answer 17

Remove ATT, groundspeed, and track errors. It has no effect on true heading calculations.

Question 18

When IRU ATT mode switch is selected, what must A/C do while IRU attitude alignment is detected?

Answer 18

Fly straight and level for 30 seconds.

Question 19

When in IRU ATT mode, the system will not supply heading information until?

Answer 19

Current heading entered on FMC POS INIT page

Question 20

What will IRS do if motion is detected during init?

Answer 20

Stops. Alignment continues and completes in approx 10 mins after motion has stopped.

Question 21

When does IRS enter SPLIT IRS OPERATIONS?

Answer 21

When aircraft passes north of 84N or south of 84S

Question 22

How long does a high latitude (POLAR) alignment take?

Answer 22

17 minutes