"I'm having a bit of a problem with the Alternative Nav scenario."
Ooops.... Not surprising ... It looks like I was reading my electrical diagrams incorrectly. I thought the L FMC was being driven by the Captain's Transfer Bus (which is dead when there is only Standby Power available) but is is actually being driven by the APU Stby Bus (assuming your aircraft has one). Although the APU Stby Bus is normally fed by the Captain's Transfer bus, when power is lost from the Main Busses, it is fed by the APU Static Inverter.
I assumed both FMC's would be dead in this scenario.... apparently not
(Good to know)
Sorry to bother you at this time of night.
Have fun in the sim anyway ;-)
Cheers.
Q.