HI DutchOne
the questions was
"Last time me and my captain where timing for GPS primary to appear after initializing the ADIRSs. It took 7 minutes."
From the Honeywell FMGS manual
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GPS Position
On the aircraft, the GPS position is not actually a pure GPS position, but is a combination of GPS and IRS position (also known as GPIRS or hybrid GPS position).
Using a combination of the highly accurate GPS position and smooth and reliable IRS position ensures the hybrid GPS position that is sent to the FMS is very accurate and stable. If the aircraft is configured for GPS and the FMS determines the hybrid GPS position has the smallest EPE, this GPS position is combined with the mixed IRS position and used for navigation (IRS/GPS). However, the FMS must first validate the hybrid GPS data.
The FMS only uses the hybrid GPS position if the GPS data has integrity and the GPS bias (the difference between the mixed IRS position and the GPS position) is within limits. The GPS bias is compared to a threshold limit that accounts for any differences between the GPS position and mixed IRS position because of the IRS drift since alignment. The integrity of the GPS data is provided by RAIM when using Honeywell ADIRUs and AIME (autonomous integrity monitored extrapolation) when using Litton ADIRUs. When integrity is no longer available because the horizontal integrity limit exceeds the threshold limit (defined by RNP and update integrity limit), and no satellite failure is detected, the FMS uses alternate integrity monitoring (AIM) to extend the use of GPS position.
If GPS position is unavailable, the FMS also applies the GPS bias to the mixed IRS position to increase the navigation accuracy. The FMS continues to use the bias in the position calculation until GPS position is again available or the EPE for the another sensor combination is smaller than the EPE for GPS position.
At any time, the pilot can deselect GPS for navigational use by pushing 5L (DESELECT GPS) on the SELECTED NAVAIDS page.
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