Very interesting thread, but a bit to scientific for me as a user.
I only know as a pilot, that the navigation system uses the so called hybrid position:
GPS POSITION
Each IRS computes an hybrid position that is a mix IRS/GPS position called GPIRS. Among these 3 GPIRS hybrid positions received by each FMGC, one is selected according to a figure of merit and a priority. The selection is performed using the following hierarchy :
onside GPIRS position
GPIRS 3
opposite GPIRS position
If the GPIRS data do not comply with an integrity criteria, the GPS mode is rejected and radio position updating is used, "GPS PRIMARY LOST" message is displayed on ND and MCDU scratchpad.
In other words the GPS position could be the most accurate, but if its outside the integrity circle, the system will reject it and revert to the less accurate rad nav, weird isn't it?
As long as GPS primary is in use, all usual required navigation performance are met, that's what the book says.
Another interesting thing is also that (subject to authority approval) having GPS Primary one can shoot a non precision approach even if the ground facility is U/S.
Does anybody know what sort of prove the operator has to provide in order to be allowed to use the vertical profile in managed mode out of the box?
Cheers.
