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

[Will.iam]

Holy cow that guy brushed with death multiple times on that flight i can only imagine the panic and anxiety he was feeling while on that roller coster blind. And then see the track data after the fact, missing mountain peaks by pure positional luck while acrobatic. That would leave me with nightmares. Time to go out and buy a lotto ticket!  Also hit home that I’m in the same situation that i get my checks through my job on advanced glass with multiple backups while doing upset recovery and haven’t practiced  partial panel unusual attitude recovery in years.  Is there a workshop / course available to offer refresher / practice for partial panel unusual att recovery?

[smwash02]

19 hours ago, takair said:

Found this link On Beechtalk….lots of new discussion there  on another event:  

https://www.tsb.gc.ca/eng/rapports-reports/aviation/2021/A21P0001/A21P0001.html

 

Either I have a confusion in my understanding of the 275 product models or there's a disconnect here. Garmin says if you have two ADAHRS units it'll auto-switch the other, like what the pilot said he expected, but TSB CA says this is not correct.

"Primary HSI" seems to be the keyword. I suppose there's a model that's an HSI without the ADAHRS? Further it says a 275 MFI was installed in the incident plane. The Garmin 275 Product Page lists a 'MFD', which is what is maybe what is meant here? I can see the MFD not having ADAHRS, it wouldn't need it.

From: Garmin's GI275 blog

You can count on the reliability of the GI 275, but primary instruments often require backups. With the installation of a GI 275 attitude indicator and GI 275 HSI, you get the benefit of auto-reversionary mode². This mode kicks in and displays attitude and heading data on the remaining HSI or MFD if an outage should occur. If that doesn’t provide enough peace of mind, then consider the GI 275 attitude indicator’s backup battery — it provides up to 60 minutes of power to get you home.

²Both GI 275 units must be ADAHRS versions to support reversionary capability

• •  

From the tsb.gc.ca site:

When a unit is configured as a primary HSI and a fault occurs with an interconnected unit, it will not automatically switch to reversionary operation mode. In addition, the pilot cannot manually select the ADI display page because it is not one of the pages available when the unit is configured as a primary HSI. Pages available for a primary HSI configuration are HSI and HSI Map; pages available for standby ADI and standby HSI include an ADI page.

In July 2020, the occurrence aircraft’s directional gyro was removed and a Garmin GI 275 MFI was installed in accordance with U.S. Federal Aviation Administration Supplemental Type Certificate (STC) SA02658SE.^{Footnote 14} This MFI was configured as a primary HSI. In October 2020, the aircraft’s attitude indicator was removed and a second Garmin GI 275 MFI was installed in accordance with the same STC, but was configured as a primary ADI. Because both of these instruments were configured as primary units, a reversionary switch was not installed, nor was it required to be.

The aircraft’s owner and the occurrence pilot both thought that if a fault was detected in the ADI, the HSI would either automatically enter the reversionary operation mode and display the ADI page, or the pilot would be able to select the ADI page manually. Therefore, their understanding of both the system’s automation and the units’ reversionary capabilities was incorrect.

 

[David Lloyd]

Your confusion is warranted, it is a complicated product.  The report appears to be accurate.  Yes, Primary HSI is the key phrase.  I think any HSI configuration is going to require a heading reference from somewhere.  When referring to the GI-275 generically, Garmin refers to it as a MFI, multi function instrument. MFD or multi function display is more specific.   From the report, it seemed as if the pilot believed the HSI would display an ADI page but it was not configured to do so.

The first GI-275 was installed in June or July as a Primary HSI with an ADAHRS and backup battery.  In this configuration, it is only and will only display an HSI or an HSI with map.  It will not in this configuration revert to an ADI.  

The second GI-275 was installed months later as a Primary ADI with an ADAHRS and backup battery.  In this configuration it is only and will only display a ADI, nothing else.

Since the Primary HSI was not (but could have been) configured as either a Standby ADI/HSI or Standby ADI/MFD, other standby instruments were required and a revisionary switch was not required.

[PT20J]

After reading the BT thread, the lack of reversion seems to be an installation configuration issue. The HSI was installed first. The ADI was installed later. They were configured as two separate instruments. With the installation of the ADI, assuming that standby instruments were removed at that time, the configuration should have been set so that the HSI would revert to an ADI if the ADI failed. 

However, the failure of the ADI is still unexplained.

Skip

[EricJ]

4 minutes ago, PT20J said:

After reading the BT thread, the lack of reversion seems to be an installation configuration issue. The HSI was installed first. The ADI was installed later. They were configured as two separate instruments. With the installation of the ADI, assuming that standby instruments were removed at that time, the configuration should have been set so that the HSI would revert to an ADI if the ADI failed. 

However, the failure of the ADI is still unexplained.

Skip

And apparently it's still not well known how to configure and operate these things, which suggests documentation or training may be insufficient.    There should be easy to ways to induce failures to check reversion behavior, too, I'd think.

 

[carusoam]

6 minutes ago, EricJ said:

And apparently it's still not well known how to configure and operate these things, which suggests documentation or training may be insufficient.    There should be easy to ways to induce failures to check reversion behavior, too, I'd think.

 

Especially for the next unknowing pilot who arrives expecting one identical device to actually back up the other one…

 

Starting to sound like there wasn’t a back-up device that should have been in the panel somewhere?

What was the back up attitude indicator when any of these devices were installed?

Best regards,

-a-

[Warren]

If there are two GI-275's with ADAHRS, the remaining 6-pack gages are not required and can be removed.  This does assume the devices are configured correctly and that may not have been the case in this instance - it is still a little hard to sort through all the mess and figure out what was configured and what really happened.

[Will.iam]

3 hours ago, EricJ said:

And apparently it's still not well known how to configure and operate these things, which suggests documentation or training may be insufficient.    There should be easy to ways to induce failures to check reversion behavior, too, I'd think.

 

Maybe to test just pull the ADI circuit breaker and see if your HSI reverts or not. 
 

[David Lloyd]

Properly installed and configured, Primary ADI and Standby ADI/HSI or Standby ADI/MFD, the Standby would revert to an ADI if the Primary's breaker was pulled, or the mandatory revisionary switch was moved from Auto to ADI.  It could also be done by rotating the big knob one click CCW.

[RobertGary1]

1 hour ago, David Lloyd said:

Properly installed and configured, Primary ADI and Standby ADI/HSI or Standby ADI/MFD, the Standby would revert to an ADI if the Primary's breaker was pulled, or the mandatory revisionary switch was moved from Auto to ADI.  It could also be done by rotating the big knob one click CCW.

That’s how mine works. I know it reverts because I’ve tested it. Also my installer installed a revertion button. But as you say the hsi has 3 modes to switch through one of which is just an adi 

[carusoam]

Looks like a great thing to have on the electronics section of a checklist…

Momentarily check that the back up attitude system is actually there and ready to go to work…

 

Your ship does have an electronics section of the checklist right?   
 

Check back-up AI is working…

setting timers

setting fuel levels

Check subscriptions are current

turn on flight recorder

plug in the WAAS ADSB in device….

Then turn everything off after the flight is over…

Keeps the battery from getting drained…

PP thoughts only, not a CFI

Best regards,

-a-

[Yetti]

On 7/21/2021 at 11:56 PM, Warren said:

If there are two GI-275's with ADAHRS, the remaining 6-pack gages are not required and can be removed.  This does assume the devices are configured correctly and that may not have been the case in this instance - it is still a little hard to sort through all the mess and figure out what was configured and what really happened.

This was the question that has not been answered:  Did the pair fail or were they misconfigured?   If you have two devices with the same code, they will fail the same way.  Thus no backup.   Backup diversity means different devices that can perform the same function.

[PT20J]

59 minutes ago, Yetti said:

This was the question that has not been answered:  Did the pair fail or were they misconfigured?   If you have two devices with the same code, they will fail the same way.  Thus no backup.   Backup diversity means different devices that can perform the same function.

If you are talking about the Canadian incident, the primary AHRS had an alignment issue. It might have self corrected had the pilot maintained a wings level attitude. The HSI was not configured as a backup and, as I now understand  that primary instruments were retained, it was not required to be. The problem was that the pilot apparently believed that it would revert and lost control of the airplane trying to get the GI-275s to display attitude when he would have been better served by setting ip a partial panel scan and getting ATC assistance.

Skip

[Yetti]

19 minutes ago, PT20J said:

If you are talking about the Canadian incident, the primary AHRS had an alignment issue. It might have self corrected had the pilot maintained a wings level attitude. The HSI was not configured as a backup and, as I now understand  that primary instruments were retained, it was not required to be. The problem was that the pilot apparently believed that it would revert and lost control of the airplane trying to get the GI-275s to display attitude when he would have been better served by setting ip a partial panel scan and getting ATC assistance.

Skip

More talking about the RobertGary incident with this thread.    Yes on the primary instruments for the Canadian or flying up to clear air to sort things out.

[alexz]

24 minutes ago, PT20J said:

If you are talking about the Canadian incident, the primary AHRS had an alignment issue. It might have self corrected had the pilot maintained a wings level attitude. The HSI was not configured as a backup and, as I now understand  that primary instruments were retained, it was not required to be. The problem was that the pilot apparently believed that it would revert and lost control of the airplane trying to get the GI-275s to display attitude when he would have been better served by setting ip a partial panel scan and getting ATC assistance.

Skip

Big question is WHY it had an alignment issue? For mems based devices I can only see exceeding sensor limitations(super severe turbulence) or some external sensor badly lying to the system. 

[David Lloyd]

37 minutes ago, PT20J said:

If you are talking about the Canadian incident, the primary AHRS had an alignment issue. It might have self corrected had the pilot maintained a wings level attitude. The HSI was not configured as a backup and, as I now understand  that primary instruments were retained, it was not required to be. The problem was that the pilot apparently believed that it would revert and lost control of the airplane trying to get the GI-275s to display attitude when he would have been better served by setting ip a partial panel scan and getting ATC assistance.

Skip

You probably meant to say the primary instruments were required to be retained.

12 minutes ago, alexz said:

Big question is WHY it had an alignment issue? For mems based devices I can only see exceeding sensor limitations(super severe turbulence) or some external sensor badly lying to the system. 

The report did not have an answer, it seemed that Garmin did not respond to that question.  Canada, January, mixed rain and frozen precip on the ground, clouds at 15,000'.  Could something freezing be a factor?  Not just the pitot tube, moisture in lines?

[RobertGary1]

18 hours ago, David Lloyd said:

You probably meant to say the primary instruments were required to be retained.

The report did not have an answer, it seemed that Garmin did not respond to that question.  Canada, January, mixed rain and frozen precip on the ground, clouds at 15,000'.  Could something freezing be a factor?  Not just the pitot tube, moisture in lines?

In my case it’s almost certain that the AHRS failure was caused by a blocked pitot tube. But why it did not successfully revert to using gps track is something Garmin has been looking into. Logs show strong 3D gps signal in my case. 

[David Lloyd]

Robert,

Yes, your blocked pitot certainly was the first link in the chain of realignment.  Your picture did show gps TRK.  Pitot, heading, altitude, track, each should back up the other, but didn't.  I told my shop the airspeed, altimeter and turn coordinator  (Stec 60-2) would be staying in the my panel for at least a year. Garmin has sold a pile of these things.  Looks like they would be a little more eager to share information.  

19 hours ago, alexz said:

Big question is WHY it had an alignment issue? For mems based devices I can only see exceeding sensor limitations(super severe turbulence) or some external sensor badly lying to the system. 

Dynon Skyview has a limit of 150 degrees per second limitation of combined pitch, roll and yaw.  In the RV, a simple aileron roll or loop would not exceed that.  A split S or Cuban could sometimes get ahead of the AHRS.  The AI would just lag behind some.  Garmin does not publish such a limitation, just says to turn it off before aerobatics.

[201Mooniac]

Looks like Garmin is addressing the issue for dual GI-275 systems without another backup attitude system:

GI 275 Multi-Function Instrument Software Version v2.41 Update

September 24, 2021

• Service Document Notifications

PRODUCTS AFFECTED:

Aircraft modified with the GI 275 Multi-Function Instrument AML STC SA02658SE, MDL Revision 12 or earlier with a single pitot-static system that are equipped with dual GI 275 ADAHRS (Air Data & Attitude Heading Reference System) products [011-04489-10, 011-04489-20] installed as the only means to determine aircraft attitude.

CERTIFICATION AUTHORIZATION:

STC SA02658SE MDL Revision 13

COMPLIANCE:

Mandatory: This STC Service Bulletin must be incorporated for affected installations. This service bulletin is recommended for all other installations.

WARRANTY INFORMATION:

This modification is only warranty reimbursable for installations described in the Products Affected section.
Warranty reimbursement deadline is February 28, 2022.
Note: Installations completed after September 24, 2021 are not eligible for warranty reimbursement.

PURPOSE:

This STC Service Bulletin provides notification of STC SA02658SE Master Drawing List Revision 13 update which includes GI 275 Expansion Board Software improvement to provide additional robustness for the GI 275 ADAHRS solution.