LXNAV S100 went bonkers

[David S]

A couple days ago I was checking my pneumatics for leaks using the standard process.  While applying external pressure to the pitot I happened to notice that the S100's wind pointer was spinning like crazy.  Then I checked the other screens, and the AHRS was going nuts.  Sometimes it indicated an inverted attitude, at other times an extreme bank angle, and occasionally flipping 180 degrees quite suddenly.

WTF!

I understand that the S100 vario and HAWK wind might get confused by non-sense inputs (ASI says 50 knots while TE says zero speed), but doesn't the AHRS depend on the gyros exclusively?  Why would crazy pneumatic readings affect the gyros?

And I think this has real-world consequences:  if I get caught in bad weather and the pneumatics fail due to rain or ice, I would sure like to be able to use the AHRS to get down safely.

The AHRS has always been fine in flight, and it worked fine during my leak tests as long as the pitot was open to static pressure.

I am running software version 9.38.  I tried updating to 9.52 today, but it did not go well.  More on that later in a separate thread.

Any thoughts on this?

Other than the AHRS insanity, using the S100's ASI for leak checking is great.  You can spot a small leak as the digital readout goes from 50 knots to 49 knots over 10 or 20 seconds, whereas on a steam gauge you could be wondering if the needle had really moved, and you might wait 2 minutes to be sure.

   ...david

[Morgan Hall]

Unfortunately this wouldn't be the first time that a vendor used multiple inputs aside from the ADHRS sensors.  I believe Dynon also did this on some older glass panels that they produced and it could result in loss of control.  And never forget that Boeing did something along these lines on the 737-Max with MCAS relying on AOA data.  

It is why the ADHRS on an LX is not certified for IFR, but still is probably better than nothing if you screw up bad enough to end up in IMC.  Although I'd venture to guess that most of us are not practiced enough on hand flying off the instruments to stay oriented in the event of inadvertent IMC.  It's a fairly perishable skill and for people that only fly gliders, they may not have ever even practiced it.

Morgan

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[the_gle...@msn.com]

I have nothing to suggest about the problem, but wanted to comment on the AHRS in the LX9000. In the UK glider pilots have always been allowed to fly in IMC and we can have a 'Cloud Flying Rating'. I have used the AH in the LX9000 without problems for planned flight in IMC, either for thermalling up into cloud or for descending from wave through cloud. I now have an S10  with AHRS (and Hawk) as a backup so that I have two independent AHRS devices, one of them with an internal backup battery, for greater confidence that I will not lose Attitude and Heading reference while in IMC.