http://en.wikipedia....stem_malfunctions
Blocked static port
A blocked static port is a more serious situation because it affects all pitot-static instruments.[6] One of the most common causes of a blocked static port is airframe icing. A blocked static port will cause the altimeter to freeze at a constant value, the altitude at which the static port became blocked. The vertical speed indicator will become frozen at zero and will not change at all, even if vertical airspeed increases or decreases. The airspeed indicator will reverse the error that occurs with a clogged pitot tube and cause the airspeed be read less than it actually is as the aircraft climbs. When the aircraft is descending, the airspeed will be over-reported. In most aircraft with unpressurized cabins, an alternative static source is available and can be toggled from within the cockpit of the airplane.[6]
:-(
But it sounds like the ADIRU might have been at least part of the issue ... http://en.wikipedia....al_Reference_Unit
Cheers,
Scott.