AHRS love fest?


Apparently a "terse" writer
Staff member
I hate to break it down, but AHRS is the suckiest system on earth. Nothing like being on final approach with calm winds then your map starts shifting, then you have MAP FAIL and have to revert to raw data.


Eclipse Aviation Selects Crossbow AHRS for Eclipse 500 Jet
Thursday January 29, 7:43 pm ET

SAN JOSE, Calif.--(BUSINESS WIRE)--Jan. 29, 2004--Crossbow Technology, Inc., leading manufacturer of MEMS-based sensor systems, today announced that they have signed a long-term contract with Eclipse Aviation Corporation for production and delivery of the AHRS500GA, solid-state Attitude and Heading Reference System (AHRS). The AHRS500GA will provide the Attitude and Heading Information for the Eclipse(TM) Avio(TM) system on the Eclipse 500(TM) jet.
Proven Crossbow AHRS500 Already TSO'd and STC'd on Multiple Aircraft

The Crossbow AHRS500GA is an FAA certified, high performance, solid-state attitude and heading reference system intended for general aviation aircraft. This high reliability inertial system provides attitude and heading measurement for glass cockpit or EFIS displays, as well as for other Avionics applications. The FAA Certification, achieved in early 2003, includes TSO 4 (Bank and Pitch) and TSO 6 (Heading). The AHRS500 Certification also includes an STC to install the AHRS500 for retrofit on over six hundred different aircraft.

Dean Johnson, Vice President for Inertial Systems, says "Crossbow is the first and only company to FAA certify a low-cost, stand-alone AHRS that meets all the FAA TSO certification requirements. Crossbow is pleased to be selected by Eclipse as the AHRS for their revolutionary high performance aircraft. This selection builds on Crossbow's successes in AHRS retrofits of high performance singles and twins."

Key Component of Eclipse 500 Avio Delivering Total Aircraft Integration(TM)

As part of the Eclipse Avio system for the 500 jet, the AHRS500GA will include a certified remote magnetometer as well as additional communication interfaces for ARINC429 and RS-485. The AHRS500GA will aggregate and route data communications for the Air-Data and GPS receivers to the cockpit display.

"Crossbow has the most robust and reliable Solid-State AHRS technology in the industry," said Vern Raburn, president and CEO of Eclipse Aviation. "The fact that the Crossbow AHRS can continue to provide attitude and heading information in the absence of GPS or AirData input is especially impressive."

About Crossbow Technology

Crossbow Technology, Inc. is the leading supplier of low-cost, intelligent digital sensor solutions. Crossbow's sensors integrate silicon micromachined (MEMS) technology with digital signal processing and wireless technology. The sensors incorporate the company's proprietary SoftSensor(TM) embedded firmware, which includes algorithms for stabilization and navigation applications coupled with internal compensation and communication functions. Crossbow designs and manufactures General Aviation inertial products at its FAA approved manufacturing facility located at 41 Daggett Drive, San Jose, CA 95134. Telephone: 408-965-3300. Fax: 408-324-4840. Email: info@xbow.com. Visit Crossbow at www.xbow.com

Eclipse Aviation Corporation, Eclipse, Eclipse 500, Avio and Total Aircraft Integration are trademarks of Eclipse Aviation Corporation.
50% of the time we have HDG flags right up until we get to the hold short lines. The two AHRS systems won't align the heading properly. Or even better, at acceleration altitude, get a HDG flag and master caution when you start the turn since it shifted.
Does your AHRS occasionally get 'lost' go in the D/R (dead reckoning mode) and start doing interesting and creative things with the map profile?
Not really. The only thing it's ever done really out of the ordinary was go out completely on my side for like 10 seconds while flying a visual into MDW, only to come back on and be just fine. We just have variations of the EHSI (rose mode, arc mode, radar mode), so the big thing that is normally effected is the heading alignment.
Out of the 120 -88's and 16 -90's we have, only about 12 -88's still have AHRS.

The newer laser-ring gryo IRS's are phenomenal. Ahh!
very little, if any, XTK error.
`I love the occasional black outs usually on touchdown adding a little distraction for extra degree difficulty points.... 9.5... 9.0....10.0... 8.5... 9.0
Doug I'm confused here. The CRJ would get FMS DR if you forgot to switch back to white needles, and the FMS on the 737 would drift when the GPS coverage was poor, but I have never, ever seen any AHRS problems airborne.

We used to get EFIS COMP FAIL when we were holding short of runway 22 at LGA because of sitting on all that metal but that was it. Is this one of those MD things? I guess not if Matt is getting it in saabs, too.

We are referring to Attitude-Heading Reference System - correct?
If your AHRS system uses GPS to calculate its position it is probably much more reliable than the DME/VOR/ILS based line of sight systems. If the DME/VOR/ILS based AHARS cannot receive valid inputs from the required navaids...the MAP will fail and will, as Doug said, resort to a Dead Rec mode.

A GPS based AHRS sounds much more reliable to me...

I would guess that this would explain the difference in observations between the two systems.
I don't know squat about these systems, but I got a cockpit tour of a Citation X the other day from a friend of mine: cool stuff, I tell you. I think he described the nav system as using a combination of GPS/DME-DME-DME/ and VOR-DME. The computer chooses what it believes to be the best solution of the three calculated locations. He said that typically it uses the GPS solution, but the DME-DME-DME triangulation method is very accurate also.

Gotta love those glass cockpits!
I have never heard of AHRS using GPS. It is supposed to be Gyro based.

In the CRJ and 737 it is used only for the DG and the Attitude Indicator. GPS usage would just throw another monkey in the wrench wouldn't it?
I have never heard of AHRS using GPS. It is supposed to be Gyro based.

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I think you're thinking of INS.

AHRS is more or less a crazy DME receiver that, with a given LAT/LONG triangulates it's position with position circles from VORTAC DME's and ILS-DME antennas. Almost like the way GPS works, but instead of using satellites, it's just ground based DME data.
I think you're thinking of FMS.

AHRS uses sensor data such as pitot-static system, directional gyros, magnetic compass, etc. to align your flight instruments.

At least it does on the jets I flew, which were the CRJ and B737-700.

FMS uses DMEs to triangulate your location in horizontal space.

Now there was a doohickey called IRS on the 737 that used GPS as a starting point and then located the aircraft, but this was for FMS purposes only - Inertial Reference System.
There are differnt model numbers of AHRS and they each use different ways to align themselves.
FMS is more or less the hardware that interprets inputs from an AHRS, GPS, IRU or IRS into navigable information.

AHRS does use gyros just for attitude information for your flight instruments. But for lateral displacement triangulates using DME data from receivable VORTACS and ILS/DME antennae. Honestly, if your unit can't receive DME information, it'll freak out and go into dead reckoning mode. AHRS + an FMS head is little more than a rich man's RNAV.

IRU's use laser-ring gyros that more or less work off of the physics behind accelerations in a particular axis 'bending' the light and translates that into lateral and vertical displacement.

IRS's use physical gyros that translate gyroscopic precession into displacement.

So you can have an FMS head in your aircraft, but it's using gyros for pitch & roll information, but the lateral displacement is determined via GPS.
I think we're arguing about semantics and names

Ok I dug out all my old manuals and what you are calling AHRS and I am calling FMS are actually called the DCUs (2 of them) on the CRJ. Stands for Data Concentrator Units. These collect information from AHRS, DME, GPS and IRS if available. They are then passed on to the various display processors. The FMC controls (and is controlled by) the FMS head and display.

The FD (bars) are controlled by combined inputs from the AHRS and FMC.

Man that's a lot of initials!