Greetings,
I see that you are located in Qatar so your aircrafts are equipped with the Thales FMS2, they should have given a pilots guide....
We have to understand why Airbus decided to Hybrid both signals, ie IRS, GPS.
Because for short term the IRS is extemely precise, whereas for long term the GPS is more precise. So hybridation gives the best compromise.
As far as drift is concerned, forget about it.
Basically, positions a compared along with the HIL FOM from the GPS reciever and these values enables tne FMS to elaborate what is the IRS drift and noise.
But as a pilot I dont think you need to go into that level of details.
