I doubt the ISIS (3-in-1 Standby Instrument) was fully lost: only the Airspeed part as the Attitude is a separate electric gyro powered by the DC Essential or Hot Battery Bus. ISIS Altitude is raw data from the standby static vents (does not go through Air Data Modules) - While pitot icing is likely I feel it is unlikely that the static vents iced up too. So ISIS attitude and ALT should have been reasonable. At the very least ISIS Attitude should have been good
29 pages before some decent information on Airbus' standby instrument.Putting bomb/fire theories aside,they either:
a)encountered weather phenomenon that was beyond recovery
b)encountered recoverable weather phenomenon but didnt have the tools(attitude reference) to get out of it
c)encountered recoverable weather phenomenon,had attitude/N1 and GPS alt/GS to fly the unreliable airspeed procedure in theory,but failed to achieve it.Is the procedure feasible at max cruise alt?Its drawn up for climb phase(below/above FL 100) with 5 deg as initial target.Unreliable airspeed at max cruise alt,and you descend to improve margins!
Not enough discussion/focus(IMHO) on:
-ISIS;what did they have in the way of basic instrumentation.Can the ACARS messages give a defintive answer on this?
-both PFD's disabled?ACARS messages prove this?In the Adamair crash,the Captain killed everyone simply because he didnt hand over control to his First Officer who had reliable flight instrumentation.
-mechanical gyro versus laser gyro-
-standby instrumentation philosophy;independent,self-contained,standby inverter powered,integral lighting,"old-school" technology(simple mechanical gyro,no interface with ADM)..not one mechanical gyro installed on these high-tech aircraft including B777..does it break the KISS principle?Why not have a third mechanical gyro on center panel for triple redundancy?
-wx radar interpretation..training is woefully inadequate
-this obsession with modern pilots for climbing as high as they can, above opt alt,like its a game or badge of honor..I see it all the time.They set max alt-300/400' into the step clb box and say "We can get above this and save some fuel as well".In turbulence,you generally descend,unless you're already below opt alt(light) and/or PIREPS indicate climb is favorable.
-Interflug's discussion on weight has all but been ignored/dismissed..take off was at max weight..payload calculated on standard weights,not actual..assume overweight condition and treat FMC-generated opt alt with a degree of suspicion..mentally adjust by -1000 and take another 2000'(or more) off when turbulence is en-route.
-Diversion strategies..ie divert early on,dont climb above,once you take a decision dont back down,theres no shame in a fuel stop after diversion.