What is the power source for the ISIS? Does the loss of ISIS along with the ADIRU fault and the reversion to ALT Law indicate a total loss of electrics?
(yes, I know the process is Normal to Alternate to Direct and then with all loss the THS, rudder and FADEC engines. And yes, I understand we are talking loss of both eng generators, no APU, a failure with the RAT and loss of battery power)
Most standby inst packages I have flown were independently powered.
Cause unknown but are we talking about an electrical fire that quickly took out all instruments as well as flight control computers? We saw in Swissair 111 and ValuJet that inflight fires can evolve VERY quickly offering little time for a solution and rapidly diminishing control.