As a mere avionics engineer I'm baffled. If the Inertial reference System loses its position in flight it is seriously unserviceable, so why would you want to realign it?
Remember, the new systems are not using clumsy space-stabilzed" gyro platforms and are bolted to your plane's frame. Back in those golden days 40 years ago, we typed in our coordinates and the system compared sensed values with predicted values for that geo-referenced position in space.
So what makes you think that a "strap down" system doesn't need to know its starting orientation in inertial space? What do you think it does with the coordinates that you type in?
