Rob Logan writes:
<<the more expensive Crossbow 500 which is purely inertial
the 500 uses both gps and airdata for aiding. this was added
in CFS v4.1 and refined in CFS v5.0 early 2004. CFS spent
quite abit of time at xbow, on CFS expense to refine this
aiding. its a long story. you can see the hole aiding packet
received via 232 in the xbow manual on page 30
http://xbow.com/Support/Support_pdf_files/AHRS500GA_Operators_Manual.pdf
this reduced acceleration errors, commonly seen as a tilt on landing.
>>

Rob's post piqued my curiosity which sent me to the Xbow site to download a 420 users manual. In the introduction section I found:

<< The integration of a GPS receiver provides more information for the extended Kalman filter, allowing it to provide better corrections for attitude determination, as well as the ability to correct for sensor errors. >>

That "ability to correct for sensor errors"  part got me thinking,  along with the talk from Xbow about having the "right" GPS antenna, what happens to a 42x in flight if the GPS signal fails and you lose the ability to "correct for sensor errors"? If the GPS is not needed then why have it? What happen if you are flying along and the system resets and the AHRS comes up before you have a GPS lock? GPS availability is very good but anyone that has flown for a while has experienced GPS outages or bad reception. 

If I had a 42x I would want to know what happens to my attitude display if I lose GPS. This could be tested by disconnecting the antenna while flying (or before a flight).

Why didn't they use airdata aiding (proven to work on the 500)?

Could the "spinning like Patty Wagstaf" reported problem be caused (all or in part) by GPS integrity failure?

I have never heard a concise explanation for the 42x problem / fix. What was broke and how was it fixed and tested to confirm it was fixed?

Anybody know?????

Regards
Brent Regan