IRS transfer switch on the 737 NG
My question is:
Loss of both Engine driven Generators, you are only on standby power and only the first officer`s primary attitude display is failed. The checklist says:
IRS Transfer switsch ..... Both on Left
What does this help?
As I understand, the left IRS is normally powered by the AC stby bus and the right IRS from the AC transfer bus 2. If AC power is lost, either or both systems automatically switch to backup DC power from the switched hot battery bus.The right IRS loses it DC power if AC power is not restored within 5 minutes.
So the left one should remain on DC power. So what does this checklist step actually do?
anyone any ideas?