Originally Posted by
Peter H
My guess would be 10s of seconds from the rejection of the unfrozen pitot to the divergence in readings from the other two pitots leading to the declaration of UAS.
Nope, it's pretty much instantaneous in human terms. The software is checking and cross-checking several times a second - you'd be talking about maybe 2 or 3 seconds from initial icing-over to the systems detecting an extended discrepancy and disconnecting AP.
In the case of AF447 the point is somewhat moot, as the PNF is supposed to monitor ECAM and action things accordingly. The PF started pulling up almost immediately the AP disconnected without first assessing the situation. The cause of AP disconnect was right there in the ECAM - but it seems that the PF's instincts overruled his reason and training, and neither the PNF or the Captain could break through his panic.