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If I have two AHRS can I get rid of my vacuum system?


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Just now, RobertGary1 said:

Now everyone can laugh at me for keeping my vacuum system. :)

Wow.  That was in flight?  Did it recover?  I’m sure Garmin will want to know about that...as you alluded to...lots of folks are relying on those guys as primary and backup!

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Posted (edited)
24 minutes ago, takair said:

Wow.  That was in flight?  Did it recover?  I’m sure Garmin will want to know about that...as you alluded to...lots of folks are relying on those guys as primary and backup!

Yes In flight. It came back for a bit, both did the slow roll of death and went back to black. 

Edited by RobertGary1
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Ha!  That’s awesome. 
It is nice to have a backup.  My stec 30 and my GTX345 ahrs are mine... the stec 30 is a reasonable backup since it’s rate based.  At least it’ll keep the wings level until you can find vmc.

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5 hours ago, RobertGary1 said:

Me today. Actually I have 3 Garmin AHRS on two displays. But they share the same software. 

7179D6B9-B3A8-417E-A963-FA079F8F1143.jpeg

Question, is your oil temp normally that high with that low of cylinder head temp? Or is your cylinder head temp inop?

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It looks like you have the "Aspen Fail". That is a failure of airspeed input leads to AHRS failure. I bet you do not have GPS input into these units. Newer or updated Aspens as well as all Garmins with GPS input will use GPS speed as a backup and keep working. You should have your avionics shop tie these into the GPS.

 

 

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1 hour ago, GeeBee said:

It looks like you have the "Aspen Fail". That is a failure of airspeed input leads to AHRS failure. I bet you do not have GPS input into these units. Newer or updated Aspens as well as all Garmins with GPS input will use GPS speed as a backup and keep working. You should have your avionics shop tie these into the GPS.

 

 

They’ve got gps trk on the heading at the bottom.  They seem to be tied into gps.  Actually, that’s probably an installation requirement like it is for the G5s, although they continue to work without it.

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I hope you can share more information as you have this looked at. The situation is a bit odd -- both instruments should have their own AHRS and pitot/static connections making them fully independent.

It is possible, as you mentioned software, that with both running the same something could trigger a bug that would affect both in the same way.

A test I would've liked to have seen would be pulling the breaker on one of them to see if it's the cross-communication that caused them to freak out. A situation I can see is where they both thought the other had failed and were arguing about what to do about it. Lacking a 3rd to establish quorum they gave up.

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4 hours ago, smwash02 said:

I hope you can share more information as you have this looked at. The situation is a bit odd -- both instruments should have their own AHRS and pitot/static connections making them fully independent.

It is possible, as you mentioned software, that with both running the same something could trigger a bug that would affect both in the same way.

A test I would've liked to have seen would be pulling the breaker on one of them to see if it's the cross-communication that caused them to freak out. A situation I can see is where they both thought the other had failed and were arguing about what to do about it. Lacking a 3rd to establish quorum they gave up.

I agree, however, do you think pulling the breaker would cut their communication? They both have battery backup.

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Wow - as far as I know, the GI 275 attitude isn't dependent on airspeed input like the pre-MAX Aspen was?   This is a distinct software glitch maybe? Curious what Garmin would have to say about it.

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52 minutes ago, Ragsf15e said:

I agree, however, do you think pulling the breaker would cut their communication? They both have battery backup.

That's a good point. Mine are on the schedule to be installed, so I unfortunately don't have the capability to test yet. Hopefully you can tell it to turn itself off? If it thinks it has no airspeed, perhaps it'll turn off thinking you're not in flight?

I'll be running a few of these scenarios. The unknowns of what could happen if they blow up in the soup would not be pleasant.

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7 minutes ago, smwash02 said:

That's a good point. Mine are on the schedule to be installed, so I unfortunately don't have the capability to test yet. Hopefully you can tell it to turn itself off? If it thinks it has no airspeed, perhaps it'll turn off thinking you're not in flight?

I'll be running a few of these scenarios. The unknowns of what could happen if they blow up in the soup would not be pleasant.

My guess is that pitot is required for the AHRS correction and shutting one down wouldn’t help. My shop said another customer had this happen when they encountered pitot icing. In the soup pitot ices up and you loss airspeed then you lose attitude. Bad day. 

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20 minutes ago, RobertGary1 said:

My guess is that pitot is required for the AHRS correction and shutting one down wouldn’t help. My shop said another customer had this happen when they encountered pitot icing. In the soup pitot ices up and you loss airspeed then you lose attitude. Bad day. 

AHRS is Attitude and Heading Reference System.

ADAHRS is Air Data, Attitude, and Heading Reference System that it would be a part of.

If you lose airspeed, it should X out the airspeed, but not the attitude.

There's another thread here about a guy who had a problem with his airspeed not working (I think it was the pitot cover was on?) and he had attitude information, which enough evidence for me to say "if the pitot/static stops working, attitude will continue on"... unless there is software issue that causes the attitude to fail if the airspeed sensor does. In your case, the chances of both having hardware failures at the same time is possible, but pretty unlikely.

Edit:

Here is the link where the video is that shows the twin 275s not having airspeed due to pitot/static cover and the devices remain functional for attitude.

Edited by smwash02
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33 minutes ago, RobertGary1 said:

My guess is that pitot is required for the AHRS correction and shutting one down wouldn’t help. My shop said another customer had this happen when they encountered pitot icing. In the soup pitot ices up and you loss airspeed then you lose attitude. Bad day. 

That was the case with old Aspen models.  Not the case with newer ones or the garmins.

The G5s use gps for Ahrs correction but continue in a “degraded” mode if it’s lost.  I have turned off my gps in flight and flew around with no noticeable degradation.

Edited by Ragsf15e
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3 minutes ago, Mark89114 said:

Except for maybe in this case???  

Maybe, but I suspect it’s some kind of software issue.  Be nice to hear from Garmin on this.

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1 hour ago, smwash02 said:

AHRS is Attitude and Heading Reference System.

ADAHRS is Air Data, Attitude, and Heading Reference System that it would be a part of.

If you lose airspeed, it should X out the airspeed, but not the attitude.

There's another thread here about a guy who had a problem with his airspeed not working (I think it was the pitot cover was on?) and he had attitude information, which enough evidence for me to say "if the pitot/static stops working, attitude will continue on"... unless there is software issue that causes the attitude to fail if the airspeed sensor does. In your case, the chances of both having hardware failures at the same time is possible, but pretty unlikely.

Edit:

Here is the link where the video is that shows the twin 275s not having airspeed due to pitot/static cover and the devices remain functional for attitude.

I've also lost airspeed and not have the attitude die. So it doesn't happen 100% of the time. 

-Robert

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46 minutes ago, Ragsf15e said:

Maybe, but I suspect it’s some kind of software issue.  Be nice to hear from Garmin on this.

Not sure if its a coincidence or not but I got my "Battery Capacity Test Required" on both units as its their 1 year anniversary.  Maybe some software tickle.

-Robert

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Called my shop. They've seen this on a G-5 before after pitot ice. So they tried running a G500, G5, and GI-275 up and down in airspeed on their test equipment. It took a little work but they were able to get the attitude to fail on all 3. So they all clearly are using airspeed in the calculations.

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Thanks for letting us know, but...

May I suggest letting the NTSB know? Ref NTSB 830, required reports.

I'm serious.... this is more than a support ticket for someone who does elect to drink the punch and remove their vaccum system, thinking two of these devcies provides sufficient redundancy for safe instrument flight

https://www.law.cornell.edu/cfr/text/49/830.5

 

(9) A complete loss of information, excluding flickering, from more than 50 percent of an aircraft's cockpit displays known as:

(i) Electronic Flight Instrument System (EFIS) displays;

(ii) Engine Indication and Crew Alerting System (EICAS) displays;

(iii) Electronic Centralized Aircraft Monitor (ECAM) displays; or

(iv) Other displays of this type, which generally include a primary flight display (PFD), primary navigation display (PND), and other integrated displays;

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