Difference between IRS and AHRS?

[Bpalmer]

IRS/AHRS

The 787 has both IRS and AHRS, so to say that the modern jets have one instead of the other is not quite right.

[FlightPathOBN]

The equipment, and hence the aircraft, knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't ( or where it isn't from where it is, depending on which is greater ), it obtains a difference or deviation.

Jazz, havent noticed too many people use Freud to describe the FMS logic

Actually, it doesnt really know where it is, it knows where it was, and uses this to estimate where it is, the foundation of the EKF, or Extended Kalman Filter.

[FrankCitX]

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.

[hans brinker]

Originally Posted by glum

Interestingly in all the replies, nobody actually defined the acronyms:

AHRS - Attitude Heading Reference System

It gives you the attitude and heading of your aircraft, and nothing more.

IRS - Integrated Reference System

It gives you the attitude and heading of your aircraft, plus navigation information: integrating the reference systems.

Various manufacturers interpret these in their own ways, adding options and using different systems to provide the information as they see fit.

Anything with a compass and horizon ball has an AHRS, even a DC3:

IRS: Inertial reference system

[hans brinker]

Originally Posted by Pvtpilot

Hope this is not a dumb question. I am still working on my ratings and I might be getting ahead of myself but can anyone tell me the difference (in a nut shell) between the two systems? (IRS and AHRS)
Looked on-line but got even more confused than I'm already am.
IRS dependes on flux-valves and AHRS is a computer generated system?
regards

Lots of people have given their version of the truth, here is mine:

IRS: Inertial reference system. Old systems used physical gyros, now replaced with laser ring gyros. After you tell the system were you are, it will keep track of where you go by adding all the the turns and accelerations. Basically only gives you position info, and as time goes on the error will get bigger.
AHRS: Attitude and Heading Reference System, gyroscopic platform that gives you your orientation, what side is up, and what direction am I going.
Lots of airplanes have all these sensors combined in different way, with more sensors, like air data attached, like AB has ADIRUs (Air Data Inertial Reference Unit) that pretty much has all the position, heading speed altitude info.

[stilton]

We had AHRS on some of our MD80s, interestingly these particular aircraft were not authorized to operate into LGA due to potential magnetic interference from the steel pier runway extensions !