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

[201Steve]

+1 for DC and VAC

 

[Fly_M20R]

On 5/19/2021 at 7:53 AM, 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.

 

 

Since you have GPS TRK on your Heading it appears you do have some GPS input to the 275's. Older Aspen's also have GPS input since from what I understand they display TRK. However their software is lacking to keep the whole system running without IAS.

Your incident is likely very unique since Garmin's AHRS software is notorious for passing a torture test that others seem to fail. A friend of mine says they may have rocket scientists doing their software.    The torture test requires eliminating the airspeed (disconnect pitot, cover it up, etc) and then doing one (two?) standard rate coordinated turns and observing if the attitude indicator stays in the bank or goes to level. It would be similar to closing your eyes and having an instructor or other pilot do the same and then ask you what the attitude is. Your inner ear would tell you your are level because the fluid in the vestibular system would have stabilized. Garmin's units stay in the bank. I do believe that they use GPS to aid in the AHRS calculation though.

I posted a video in which I forgot to remove the pitot cover and took off at night. Everything else on the GI 275's continued to work perfectly. However, I showed 0 (zero) in the IAS tape and not a red-x. Your failure may be quite different than that of a pitot cover left on or having the pitot tube ice up, specially having BOTH units end up with the same failure. Here is the link to the video:

https://mooneyspace.com/topic/36739-loss-of-airspeed-indicator-on-dual-gi-275-install-on-a-night-takeoff-in-a-mooney-ovation/

I removed the whole six-pack and vacuum system.

I am curious as to what Garmin will have to say. Could it be an issue with your installer since he has had another customer with the same failure? Extremely unusual to have both units have an airspeed system failure that would red-x both of their IAS tapes. There is likely something else going on that is not apparent in your incident.

Safe flying!

Chris

Edited May 23, 2021 by Fly_M20R

[PT20J]

On 5/20/2021 at 3:30 PM, RobertGary1 said:

How do you feel about Boeing hiring software developers in India with no aviation experience for $12/hr on the 737 MAX?

-Robert

Design and coding are two different  things. Any competent coder can code a solid, well-documented design without any subject matter expertise. My experience with software developers in India is that they tended to produce very high quality code - maybe because they knew all their American counterparts thought they produced crap and this caused them to take code reviews seriously.  

Skip

[PT20J]

On 5/20/2021 at 4:04 PM, Yetti said:

All the steps that Eric outlined work well with coders no mater what they make.  Steps were skipped and tests were not not well designed.  Overall vision was missed.

My United buddy did do a runaway trim in the Sim.   He said it took both of them hauling on the yoke to keep it flying.   Can be done if you were in good shape.   Said it was like hauling a fish in and required good team work to not auger it.

 

The MAX problem, as I understand it, was a faulty assumption that a MCAS failure would be recognized as any other runaway trim failure by the crew and the standard runaway trim procedures would suffice. 

[PT20J]

My original Aspen PFD (not MAX - I’m afraid of anything called MAX) will not keep up with heading smoothly in a 60 deg banked level turn and it goes nuts and takes a couple of minutes S&L to recover if I do a wingover with about 80 KIAS and an 80 deg bank at the top. While it is recovering, it will unflag before it begins to display correct attitude.

Here’s an interesting AC…

AC_20-181.pdf

Skip

 

[Yetti]

3 minutes ago, PT20J said:

The MAX problem, as I understand it, was a faulty assumption that a MCAS failure would be recognized as any other runaway trim failure by the crew and the standard runaway trim procedures would suffice. 

Well like the forgetting to reset the Mooney trim and pouring the coals to 200 or 300 horses he said it was not a trivial thing to be encountered low to the ground.

[carusoam]

New MS feature...

Automatic download and display...

I read Skip’s .pdf file without having to go through any additional effort...

 

Go MS tech team..!

Best regards,

-a-

[PT20J]

2 hours ago, carusoam said:

New MS feature...

Automatic download and display...

I read Skip’s .pdf file without having to go through any additional effort...

 

Go MS tech team..!

Best regards,

-a-

Great!! (Now, if we could just get a good search engine.....)

[carusoam]

The search has improved over the years...

Somebody mentioned something about QQQ.  
 

Later I went to go find that thread again...  but the three letters weren’t enough to go on...

Now I can find how to afford my next Mooney... according to that guy...   

 

We also still need a way to Mark great posts...   the O’tree request...

Maybe one day...

Best regards,

-a-

[Fly_M20R]

On 5/21/2021 at 8:55 AM, GeeBee said:

No, but as you programmers say, "Garbage In, Garbage Out". The software can be just fine, but it's not getting the correct data, like a GPS ground speed which comes from a single source which is going to cause both units to fail....identically.

My point is this, before we blame the software, let's make sure the unit is correctly installed, and correctly configured. We have already discovered as I pointed out at the beginning of this thread, no airspeed input (the big red X was the clue). Now one has to figure out why the GPS ground speed back up did not work and I would look at the data input before the software. (Remember it was data input that kicked off this problem) Software is the last place I would look because it is well tested. There are several iterations of. the GI-275 software that can be loaded, but again that would be configuration error, not software defect.

I commented on this because when I was a kid, I used to work at an auto supply. When an engine was running badly, the first thing people would say is, "must be the carb". Most people would not know an idle tube from a main jet but when at a loss, they blame the thing they don't know or understand.

So let's make sure all the inputs are there and the configuration is correct before we go blaming the coders at Garmin.

 

 

Fully agree with GeeBee. I have posted a video of my taking off at night with the pitot tube covered and losing airspeed input. My dual 275's having replaced the six-pack performed flawlessly and continued to display Attitude, Magnetic Heading, Altitude as well as slip-skid indication. No standard rate turn bugs since had no TAS. 

As I wrote the above, I realized that RobertGary1's failure also did not show magnetic heading. It showed GPS Track instead. Why did it lose MH? There is no reason for the GMU11 to have lost connection. If it were to fail completely then it should have been a red-X everywhere.  I believe along with GeeBee that the culprit is an installation/configuration issue. 

Regarding installation issues, I had an issue with my install initially where the autopilot (KFC150) would not couple with the ILS glideslope. It would couple with an LPV glidepath. It turns out that the CDI output from the 530W remained connected to the KFC150 while also connected to the GI 275 ADAHRs+AP top unit. The autopilot could not resolve the dual commands in an ILS. Once the 530W CDI connection was removed from the KFC150 everything works perfectly. It was caught quickly by the installer. 

The GI275 installation requires significant attention to detail by the installer. 

CK

 

Edited May 25, 2021 by Fly_M20R

[Fly_M20R]

On 5/20/2021 at 6:49 PM, LANCECASPER said:

Although the problems are different, others are having challenges with the GI-275. I imagine that any new product as comprehensive as the GI-275 is going to have teething pains.

https://www.beechtalk.com/forums/viewtopic.php?f=21&t=194355

After reading the post and comments I believe that the issue is with the autopilot or connections to it. When I installed my dual 275's I had the KFC150 checked out by Midcontinent and they found a few bad capacitors and also took it to an "overhaul" status without actually doing a full overhaul. The whole setup works amazingly well now!!

I am reminded of a cartoon I once saw when the IBM 360 came out (quite a while ago!!!) that had a malfunctioning mainframe being checked out by a tech because the scientists using it couldn't figure out the problem. He looked behind the mainframe and pointed to a disconnected power cord from the wall....

[RobertGary1]

12 hours ago, Fly_M20R said:

Fully agree with GeeBee. I have posted a video of my taking off at night with the pitot tube covered and losing airspeed input. My dual 275's having replaced the six-pack performed flawlessly and continued to display Attitude, Magnetic Heading, Altitude as well as slip-skid indication. No standard rate turn bugs since had no TAS. 

As I wrote the above, I realized that RobertGary1's failure also did not show magnetic heading. It showed GPS Track instead. Why did it lose MH? There is no reason for the GMU11 to have lost connection. If it were to fail completely then it should have been a red-X everywhere.  I believe along with GeeBee that the culprit is an installation/configuration issue. 

Regarding installation issues, I had an issue with my install initially where the autopilot (KFC150) would not couple with the ILS glideslope. It would couple with an LPV glidepath. It turns out that the CDI output from the 530W remained connected to the KFC150 while also connected to the GI 275 ADAHRs+AP top unit. The autopilot could not resolve the dual commands in an ILS. Once the 530W CDI connection was removed from the KFC150 everything works perfectly. It was caught quickly by the installer. 

The GI275 installation requires significant attention to detail by the installer. 

CK

 

A loss of AHRS also loses magnetic heading for the same reason your old style hsi also requires a gyro.  

Edited May 25, 2021 by RobertGary1

[RobertGary1]

On 5/20/2021 at 11:17 AM, smwash02 said:

@RobertGary1Thanks for taking us along as you work through this with Garmin.

Your ice story and the flip cover likely have correlation in what the sensor was seeing as @takairsuggested.

We'll have to see what the RCA was, but if it really is a glitch in the airspeed reading that breaks the AHRS system, it wouldn't be far fetched to expect the same code to be shared across all their products. Thus, all would break under the same scenario.

You've 'inspired' me to grab a simple electric AI gyro that isn't Garmin (the rest of my stack is) to protect myself as I finalize my vacuum system removal. An AV-20 or AV-30 probably.

Looking through the docs it appears that the av-20 and 30 also uses pitot and static to correct drift. Not sure if this could happen to them too. I’ve lost pitot before with Garmin and didn’t get this response so it could be vulnerable but not every time. 

[PT20J]

My understanding is that AHRS will drift during acceleration if the Kalman filter doesn't have a velocity input from either GPS or an air data computer (ADC). The most robust system would use both. Garmin ADAHRS includes an ADC and the G5 requires a GPS input, so it could use both, but I don't know if it does.

In the "good old days" you could figure this stuff out from the Theory of Operation section of the repair manuals. But as all the Garmin modules are Line Replaceable Units and not field repairable, this level of detail isn't published since pilots don't care --right?

Skip

[Fly_M20R]

5 hours ago, RobertGary1 said:

A loss of AHRS also loses magnetic heading for the same reason your old style hsi also requires a gyro.  

As per the GI 275 manual you are correct: “Any failure of the AHRS sensors results in loss of attitude and heading information and failure of ADC sensors results in loss of air data information (indicated by red ‘X’ flags over the corresponding flight instruments).”

Question remains as to why loss of AHRS with loss of IAS on BOTH units simultaneously? I am leaning significantly as to the problem being due to an installation/wiring problem.

I am going to do a test flight and video where I cover up the pitot tube and then remove 530W GPS input and thereafter VFR GPS input as well and see what happens to my units. Hopefully can report back within a week.

[Ragsf15e]

3 hours ago, Fly_M20R said:

As per the GI 275 manual you are correct: “Any failure of the AHRS sensors results in loss of attitude and heading information and failure of ADC sensors results in loss of air data information (indicated by red ‘X’ flags over the corresponding flight instruments).”

Question remains as to why loss of AHRS with loss of IAS on BOTH units simultaneously? I am leaning significantly as to the problem being due to an installation/wiring problem.

I am going to do a test flight and video where I cover up the pitot tube and then remove 530W GPS input and thereafter VFR GPS input as well and see what happens to my units. Hopefully can report back within a week.

I’ve been wanting to do that as well but haven’t figured out an acceptable way to “lose” pitot input.

[RobertGary1]

4 hours ago, Fly_M20R said:

As per the GI 275 manual you are correct: “Any failure of the AHRS sensors results in loss of attitude and heading information and failure of ADC sensors results in loss of air data information (indicated by red ‘X’ flags over the corresponding flight instruments).”

Question remains as to why loss of AHRS with loss of IAS on BOTH units simultaneously? I am leaning significantly as to the problem being due to an installation/wiring problem.

I am going to do a test flight and video where I cover up the pitot tube and then remove 530W GPS input and thereafter VFR GPS input as well and see what happens to my units. Hopefully can report back within a week.

I've been flying this system for over a year including with a couple pitot problems. This is the first the failure has caused an AHRS issue. You may have to try a lot of times.

[Fly_M20R]

1 hour ago, Ragsf15e said:

I’ve been wanting to do that as well but haven’t figured out an acceptable way to “lose” pitot input.

I shall report back after my test flight.  May not be able to do it till next week though. 

[Fly_M20R]

1 hour ago, RobertGary1 said:

I've been flying this system for over a year including with a couple pitot problems. This is the first the failure has caused an AHRS issue. You may have to try a lot of times.

Hopefully one thorough flight test will be sufficient.

[carusoam]

Wishing you a Nice sunny day...   

Best regards,

-a-

[RobertGary1]

4 minutes ago, Fly_M20R said:

Hopefully one thorough flight test will be sufficient.

I’m thinking the gusty strong winds May have affected it. If they expect to use gps track to guess air speed. 

[Fly_M20R]

9 hours ago, RobertGary1 said:

I’m thinking the gusty strong winds May have affected it. If they expect to use gps track to guess air speed. 

Interesting thought. May have to do two tests - one w smooth air and the second w turbulence. 

[RobertGary1]

Btw it did come back briefly and went out again.

 

 

Edited May 26, 2021 by RobertGary1

[Ragsf15e]

1 hour ago, RobertGary1 said:

Btw it did come back briefly and went out again.

 

 

It’s awesome that it works in 90 degrees of bank.

[carusoam]

Yikes...

That is head turning!

Gravity on...

-a-

Roberts’s pic...