Right IRS DC Power Supply System (737-400)

[dri737]

Dear 737 drivers,

I was wondering why the Right IRS DC Power Supply System is required to perform a dual channel autopilot approach (as per MEL)?
Is it linked to the bus powering the DC backup system?

Thanks a lot for your replies!

[eckhard]

It’s been a long time but here’s an educated guess:

Both IRSs are required for a dual channel AP approach.
In the event of loss of AC power to the IRSs, the Left IRS has a dedicated supply from the battery bus.
To keep the right IRS going, a separate DC supply would be required.

Sounds reasonable?

[Banana Joe]

Following a loss of AC power source, the right IRS will be powered by a DC power source (can't remember which now) for 5 minutes, then it is shut off to prevent quicker battery discharge.