Speedbird715
This is what we're being taught in flight school right now:
IRS / INS / IRU are essentially different names for stable platforms which provide
1.) pitch, bank and yaw information by using whatever fancy gyro / l@ser technology suits the budget
2.) position information by mathematically integrating data which was received from accelerometers strapped to the platform
In modern airlines there are ADIRU units which couple IRUs with an air data computer to feed the complete flight data package directly to the EFIS.
I would have to aruge it's close but not quite right. As has already been pointed out, a INS will navigate while a IRS won't. The IRS/ADIRU provides information to the FMC and the FMC then used the "refined" position it calculates to navigate. That information is then used in the ND.
411A
The original Litton INS units demonstrated a maximum guaranteed radial error limit of 2 NM per hour of operation.
I never heard that figure. I always remembered 3 + 3T was the limit. With T being the time the INS has been in NAV.