This answer is reflective to the options we have on the Citation X:
- AHRS is a solid state system that gives you heading and attitude information.
- IRS is a laser ring gyro system with moving parts that give you heading and attitude information AND backup position information.
Both system use GPS as a primary source for position. The IRS has the advantage of having the IRS itself as a backup to the GPS. But both systems can be backed up by traditional VORs for contingency scenarios.
My experience has been that AHRS systems are more reliable and less prone to braking down. Once you have a IRS down you can’t fly RVSM and are stuck until you get that box replaced…which costs a lot of money. And giving up on the position backup that the IRS gives is totally worth it in my opinion. You have two GPS and radio nav as backup and that is more than enough. Happy to hear other opinions on the matter of course.