IRU

Also from: Inertial reference unit

IRU 1 and 2 have different power sources.

Modes

Power-up	when IRU is energised or reset
Alignment (stationary or alignment-in-motion)	IRU automatically selects the correct alignment mode (takes 5-17 minutes, or 15-30 minutes in AIM)
Auto realign	selected when stationary
Navigation	remains until system is turned off
Attitude (reversionary/erect or alignment-in-motion/attitude)	attitude data available, positional data unavailable
End of flight	after aircraft has been stationary for 5 seconds

IRS 1/2 FAIL - both IRUs fail or suffer loss of power