GPS updating of IRSs
Spooky,
My current type, the A320 uses the blended position referencing to the most accurate position, usually the GPS. I used to fly the 747-400 which did something very similar, but just different enough to differentiate the types. I've also previously flown a 747 Classic which used a Marconi FMS900 fed by receivers various and a Litton IRS (Type unknown). The Litton was position updated by the FMS, usually the GPS position. Also, I've flown a military large type which had a military FMS800 (can't remember the manufacturer) fed by what was known as an EGI. Embedded GPS IRS which did update the IRS position from the GPS constantly and was the most accurate system of all.