During recent beta testing of a new TCAS/IVSI gauge, a few questions were raised about PIC airplane system programming.I.e....1. Which AC Elec busses do the IRS's use?2. Does PIC have any HMG's? (Sorry, I'm not sure if I've asked this before)3. In the Rad Alt Failure scenario, do all Rad Alt's fail... or only one/two.... If the Left Rad Alt failed, I would have expected a warning flag on the Captain's Rad Alt Indicator(?).... or did the fail flag fail :-) Also, which busses do the Rad Alts use?4. Why does the Instrument Source Select Switch for the F/D's switch IRU's?5. Should the IVSI operate in IRS ATTitude Mode in the air? (On the real aircraft, the IVSI fail flags disappear when the artificial horizons appear on the EADI's... on the ground, at least).Any/all answers welcome.Thanks.Cheers.Ian.

Ian,Normally the IRS operate on AC power from the left and right electrical systems. The main battery is used as an alternate power source.

"Normally the IRS operate on AC power from the left and right electrical systems."Thanks, Ryno, but I was hoping for a little more info, such as....L IRU on Left Transfer Bus (with the possibility of Hydraulic Motor Generator back-up)C IRU on Autoland/Center AC Bus.R IRU on Right Bus.Some of our aircraft are set up this way.We were discussing what would happen if, say, the Left Main AC Bus completely failed (with no power automatically coming from the Right Main AC Bus).I figured out from wiring schematics that the Center Bus should not operate under these circumstances (Normally this bus is powered by the Left Bus, but can be powered by the Standby Inverter under certain circumstances... but Left Bus failure wasn't one of them).Cheers.Ian.