FlightPathOBN
ahhh..I see, I was thinking the 37's NG, which have a GPS updated IRU...
Honeywell Inertial Ref system is standard on many Airbus and Boeing models...
"Three Air Data Inertial Reference Units (ADIRUs) each comprise three ring l@ser gyros and three quartz accelerometers to accurately sense aircraft position and attitude. By integrating data from the inertial sensors and Global Positioning System (GPS), ADIRS provides automatic initialization, faster align times and 100 percent availability of Required Navigation Performance approaches."
Air Data Inertial Reference Unit - Wikipedia, the free encyclopedia
I can't speak for the Airbus but like Denti says I don't believe the GPS does update the IRS position, at least not on the 737NG, it does however update the FMC position. I can only add to the anecdotal evidence in that while I've seen the FMC and GPS position to be pretty much on top of the a/c position, you often see the left and right IRS wandering off in different directions and on long flights easily 3-4nm off the FMC computed and GPS positions.
The reference above to GPS used with the ADIRS is only referring to the initialising and alignment where the GPS position is manually inputted into the IRS system for the initial alignment.
I'm struggling to find an explicite statement to that affect that the GPS doesn't update the IRS for the 737 but I'm likewise not able to find anything that aludes to the contrary which I would think there would be if that was the case. There is however quite a bit about the GPS, Radio and IRS independently updating the FMC.
Vol 2 refers to the IRS and GPS systems as being independent systems. It talks about the FMC position being derived from a mathematical combination of the positions determined by the IRS, GPS and navigation radios and being updated from those sources with the GPS having highest priority. Mr Buffler also talks about the bias changing from almost all GPS to a mixture of GPS, IRS and Radio if the GPS doesn't have good satellite geometry.
Using these as independent sources with the bias changing depending on the quality of the position data each is providing would seem to go against the idea that one source is updating the other leading to potentially bad GPS data throwing the IRS even further off with both lots of bad data now being fed to the FMC.