[QUOTE=stilton;11188944]
Of course inertial position data is updated by GPS but, especially in light of recent events those signals can’t always be depended on
To be pedantic, the inertial position is never updated once you've aligned it and selected Nav. GPS updates the FMS position which is the PPOS that your aircraft is using. As the FMS calculates PPOS from the inputs of up to 3 x IRS, Radio aids and GPS the loss of GPS will cause the FMS posn to shift slightly as it's got one less input in the mix. RLG's and solid state accelerometers will always suffer from some small inaccuracies, so integrated over time you're still going to get some IRS drift.
I think the biggest advance in IRS technology in recent years is the ability to realign in the air for some recent equipment, something that used to be impossible.......and still is if you're taking ATPL exams ;-)