http://news.yahoo.com/s/ap/20090807/...ed_malfunction

On at least a dozen recent flights by U.S. jetliners, malfunctioning equipment made it impossible for pilots to know how fast they were flying, federal investigators have discovered. A similar breakdown is believed to have played a role in the Air France crash into the Atlantic that killed all 228 people aboard in June.
The discovery suggests the equipment problems are more widespread than previously believed. And it gives new urgency to airlines already scrambling to replace air sensors and figure out how the errors went undetected despite safety systems.