jcarlosgon:
Latest S/Ns have this:
"A backup speed scale and a backup altitude scale replace simultaneously the normal speed and altitude scales when all the three ADRs are switched OFF.
Yes, you are right. All late aircraft are delivered with standard new BUSS (Back Up Speed Scale). A380, future A350, got it also, and it could be retrofited to older aircraft as well. The pilots from Air France asked for it for their long haul fleet following the numerous speed issues (but the retrofiting is very expensive also).
There is a paper from Joelle Barthe talking about it (at the end):
http://aviationtroubleshooting.*****...le-barthe.html
S~
Olivier