A320-FMGS- GPS page indicting ground speed.
 

On the GPS page showing ground speed, is this calculated by pure change of GPS position by elapsed time? If so during ADR mismatch can I pick this ground speed (which will not be affected and be correct) and then compare it to the PFD shown ground speed. If matching with either can I safely assume that the TAS and the IAS shown on that PFD is correct? Thanks for your inputs.

GS and TAS are on the ND, not PFD.

In case of incorrect ADR, the IR is not affected.

Hence the GS displayed by ADIRU on the ND will be correct, always matching the GS readout direct from the GPS Monitor page via MCDU, irrespective of how much the ADR is wrong.

I do not think that this is correct.
The IR us using the TAS from the correlated ADR to calculate the wind speed from the GS. Consequently when the TAS is wrong in case of ADR probe blocked the GS can´t be correct. In order to see the true GS one can only open the GPS monitor page on MCDU as Aquarium said. The "Air France case" showed clearly the problem: TAS jumped from 461 kt to 182 kt and back. W/speed changed from -30 real to 249 and back.

Let,

I think you have that twisted... As ADR probes cannot, ever, measure G/S only IAS/temp etc.

Your example quotes erroneous wind read outs which will occur in an unreliable airspeed event. However G/S (measures by IRS, DME/DME, or GPS) should be correct.

aquarium1

Comparing G/S does not prove that the associated ADR is correct as ADR's do not measure ground speed, other sensors do that as I have highlighted above. Hence correct ADR indications are checked using the more traditional indications (IAS/ALT..)

Cough
Got it.thx