Originally Posted by
RR_NDB
"The proposed airspeed monitoring system would compare changes in measured airspeed over a short period of time with changes in ground speed as computed by the accelerometers and gyros in the aircraft's air data and inertial reference unit (ADIRU)."
From the published US patent application
[0007] Generally, aircrafts comprise systems comparing between them the information provided by different sensors. Thus, if most of the sensors provide a similar value, such a value could be considered as true. However, in some cases, being actually very rare, such sensors could be, either all or most of them, submitted to a similar frost phenomenon, so that the systems of the aircraft and the pilots can be without any reliable indication about speed or be unable to eliminate the erroneous speed(s).
The incorporated French patent submitted Sep 23, 2009