Originally Posted by
bille1319
You are assuming 2 things; that SatNav gives horizontal speed and ignores vertical speed components and that SatNav is unaffected by environmental aspects such as electrical weather systems. Existing Integrated INS gyros do all this successfully in vehicles such as submarines to space craft.
It is normal these days to integrate the INS and the GPS so that any wander in the INS is corrected and any outage of GPS can be covered by use of INS.
It is not a perfect system but it can provide a pseudo airspeed indication. Had it dropped in when the AF447 ADIRUs lost the plot and they just picked up a generated airspeed instead the FMC could have stayed in normal law with just an ECAM message of the airspeed sensor failure, then when they came back a minute later - the system could have reverted. I believe (someone may confirm) that the 787 has something like this built in.