IRS

Question 1

How do you select the IRU mode selector from NAV?

Answer 1

• The selector must be pulled out

FCOM, VOL 2; 11.10.10

Question 2

What power supply does the IRU’s use in normal and in backup?

Answer 2

Normal
- AC BUS 3,1,2.
Backup power supply
- DC APU HOT BATTERY BUS

Question 3

What is the function of the ALIGN position of the IRU Mode Selector?

Answer 3

When parked and momentarily selected
• Initiates alignment
• Removes sensor errors when selected from NAV mode.
FCOM, VOL 2; 11.10.10

Question 4

How long does it take for full alignment of the IRS?

Answer 4

• Approximately 10 minutes

FCOM, VOL 2; 11.20.3

Question 5

When is full alignment of the IRS required?

Answer 5

• When the time from the last full alignment to the next expected
arrival time exceeds 18 hours.
FCOM, VOL 2; 11.20.3

Question 6

How do you accomplish a fast alignment of the IRS?

Answer 6

• Airplane must be parked
• Position the selectors to ALIGN
• Enter present position
• Reposition the selectors to NAV
• Takes 30 seconds
• This action removes accumulated track,ground speed, and altitude errors,
  re-levels the system, and updates the present position.
  FCOM, VOL 2; 11.20.3

Question 7

What does the IRS ON Battery (BAT) Light mean, when displayed on the Overhead Maintenance Panel?

Answer 7

• IRS operating on backup electrical power from the APU HOT BATTERY BUS.
FCOM, VOL 2; 11.10.11

Question 8

Explain what happens when alignment of the IRS is lost in flight?

Answer 8

• The navigation mode is inoperative for the remainder of the flight.
• Attitude information can be obtained by moving the selector to ATT.
- IRU enters align mode for 30 seconds. (Straight and level flight)
FCOM VOL 2; 11.20.3

Question 9

What happens if the center IRU is operating on DC power?

Answer 9

• The center IRU operates on DC power for 5 minutes, then shuts down.

FCOM, VOL 2; 11.20.4