Whatever happened to using DME to find your groundspeed?
Which DME signals would they be picking up in the middle of the ocean?
GPS and IRS.
The solution for what happened is fly a "that's about right" pitch attitude with a "that's about right" power setting and accept deviations from planned speed and altitude until such time you regain reliable instrument indication.
Throw in a thunderstorm, bells and chimes, warning messages, autoflight kicking off, a stall recovery technique inappropriate for the conditions of the airplanes control software and light shined intona big black hole overlooked by the training/experience of the crewmembers sitting there web this all happened and you have an accident.
They didn't do really anything right. The French (and Brazilian) way if doing things says point fingers and lay blame. Well that's on Air France and this crew.
The bigger question is "why?". And bigger yet "how do we prevent it?"