Two A320 IRU questions
Hi all,
1. When aligning the IRU's, I've heard a popular theory/technique/procedure that they should be moved to NAV in the order 1-2-3. I've also seen 1-3-2. I couldn't find any specified order written anywhere- neither in my company manuals, nor the Airbus manuals. Is this just urban myth, or is there actually something to the order in which they're powered up?
2. Let's say we're sitting at the gate with the GPU supplying power, and the IRU's aligned, and the GPU gets disconnected. Would it be ok to leave the IRU's in NAV while starting the APU, or would it be better to switch them off until the APU is up? Either way, why?