Garmin AOA: Installation May be Unsafe

[smccray]

As part of my panel project, I installed a Garmin AOA in the plane. It seems to work well and I was happy with it, but I experienced a problem on a flight on Tuesday that makes me question the safety of the installation.

On take off my door popped open. No big deal- fly the airplane. The issue I have is that the Garmin AOA indicated an imminent stall both on the indicator mounted on the glare shield, and with audio alerts. Wind was crazy, lots of noise, and the AOA made the situation worse. I pulled the breaker, landed, and closed the door. With the door closed, the AOA began working as expected.

Investigating the issue, it appears that the GSU 25 uses three connections to determine Angle of Attack. There are two air connections to a dedicated pitot tube, and a third to the static system. The installation manual prohibits connecting the GSU 25 to the static system of the airplane. Instead, the static connection is placed near the alt static source behind the panel in a Bonanza.

When the door opened on takeoff, I believe it created a low-pressure condition inside the airplane. The low pressure caused the AOA to mis-read the AOA and to direct the pilot to reduce the angle of attack, even though the wing was flying safely. Given that this indication occurs during a critical phase of flight after a common problem with general aviation aircraft, I believe the Garmin AOA can adversely contribute to safety in this condition.

I notified Garmin of this problem yesterday and we're working through the problem. I'm not sure I have any options given the approvals for the system; this failure condition may be a feature rather than a bug. At the very least, pilots should be notified of this potential problem. I believe that the GSU 25 should be connected to the static system of the airplane for this installation to be safe. I’m evaluating options at this point, but my first reaction is to remove the system if it can’t be connected to the static system of the airplane.

[orionflt]

you could always add it's own dedicated static port

[Vno]

5 hours ago, smccray said:

As part of my panel project, I installed a Garmin AOA in the plane. It seems to work well and I was happy with it, but I experienced a problem on a flight on Tuesday that makes me question the safety of the installation.

On take off my door popped open. No big deal- fly the airplane. The issue I have is that the Garmin AOA indicated an imminent stall both on the indicator mounted on the glare shield, and with audio alerts. Wind was crazy, lots of noise, and the AOA made the situation worse. I pulled the breaker, landed, and closed the door. With the door closed, the AOA began working as expected.

Investigating the issue, it appears that the GSU 25 uses three connections to determine Angle of Attack. There are two air connections to a dedicated pitot tube, and a third to the static system. The installation manual prohibits connecting the GSU 25 to the static system of the airplane. Instead, the static connection is placed near the alt static source behind the panel in a Bonanza.

When the door opened on takeoff, I believe it created a low-pressure condition inside the airplane. The low pressure caused the AOA to mis-read the AOA and to direct the pilot to reduce the angle of attack, even though the wing was flying safely. Given that this indication occurs during a critical phase of flight after a common problem with general aviation aircraft, I believe the Garmin AOA can adversely contribute to safety in this condition.

I notified Garmin of this problem yesterday and we're working through the problem. I'm not sure I have any options given the approvals for the system; this failure condition may be a feature rather than a bug. At the very least, pilots should be notified of this potential problem. I believe that the GSU 25 should be connected to the static system of the airplane for this installation to be safe. I’m evaluating options at this point, but my first reaction is to remove the system if it can’t be connected to the static system of the airplane.

I understand why you are not happy with that situation but how often do you fly with the door open? I would not give up all the positives of the AOA system when working normally for the off chance you have a door open and it no longer works correctly. Especially now that you know and can de-power it if the door open again.

Where I fly for work we have a AOA system installed and it has saved us damaging airplanes at least three times that we know of. Probably many more that are not documented. I would not want to operate without it again.

Humble opinion

Brian

[Shadrach]

5 hours ago, Vno said:

I understand why you are not happy with that situation but how often do you fly with the door open? I would not give up all the positives of the AOA system when working normally for the off chance you have a door open and it no longer works correctly. Especially now that you know and can de-power it if the door open again.

Where I fly for work we have a AOA system installed and it has saved us damaging airplanes at least three times that we know of. Probably many more that are not documented. I would not want to operate without it again.

Humble opinion

Brian

If it happened in IMC during departure It could kill someone. Door pops are not as rare as one might think and they don’t care what the weather looks like. We had a Cirrus end up in a neighborhood in Gaithersburg because of a door pop on departure in IMC. Pilot was panicked and disoriented enough to pull the chute rather than just hit the LVL button on the auto pilot.  As an armchair critic I think that was poor airmanship but I wasn’t there.  He is still alive to tell the tale so who cares what I think. I’m pretty sure that a loud and immediate pressure change, lots of wind noise and loose papers flying around the cockpit would be disconcerting just as your getting into your scan. Adding an imminent stall indication and a bitching Betty in the background is no bueno to say the least. I wouldn’t remove the system until I had determined the issue could not be corrected but I sure as sh!t wouldn’t leave it that way either.

Edited March 29, 2019 by Shadrach

[Jim Peace]

you could have Boeing install an MCAS system.....field approval by them being that they police themselves....

 

[smccray]

3 hours ago, Vno said:

I understand why you are not happy with that situation but how often do you fly with the door open? I would not give up all the positives of the AOA system when working normally for the off chance you have a door open and it no longer works correctly. Especially now that you know and can de-power it if the door open again.

Where I fly for work we have a AOA system installed and it has saved us damaging airplanes at least three times that we know of. Probably many more that are not documented. I would not want to operate without it again.

Humble opinion

Brian

I’m not happy about it, but oh well. The bigger issue is that Garmin doesn’t include any information in the manual about this limitation on the system.

It’s non-required equipment and it’s an abnormal flight condition.  That’s the argument Garmin will make. I call BS- it’s a common abnormal flight condition that has a history of causing GA accidents.  The installation causes additional difficulty due to the way it’s installed. And worse- it’s not disclosed in the manual. 

The question here isn’t whether or not AOA is valuable.  It’s whether this AOA is safe.  This was a $1500 part installed with a 6 figure panel job. It’s the only real problem I’ve had with the equipment so I’ll call that a successful install overall.

I have an Alpha Systems kit- I may just pull the Garmin AOA altogether. 

[carusoam]

The post I didn’t finish....

 

Scott,

Nice pirep!

 

Reminds me of a certain Boeing 737 Max challenge...

Sudden failure of an AOAi sensor system, giving off inappropriate guidance to lower the nose...

But, in your plane... it didn’t automatically lower the nose...

Wise choice to disable the AOAi alarms...

[Shadrach]

9 hours ago, smccray said:

I’m not happy about it, but oh well. The bigger issue is that Garmin doesn’t include any information in the manual about this limitation on the system.

It’s non-required equipment and it’s an abnormal flight condition.  That’s the argument Garmin will make. I call BS- it’s a common abnormal flight condition that has a history of causing GA accidents.  The installation causes additional difficulty due to the way it’s installed. And worse- it’s not disclosed in the manual. 

The question here isn’t whether or not AOA is valuable.  It’s whether this AOA is safe.  This was a $1500 part installed with a 6 figure panel job. It’s the only real problem I’ve had with the equipment so I’ll call that a successful install overall.

I have an Alpha Systems kit- I may just pull the Garmin AOA altogether. 

Does anyone else fly your bird? You’ve been through it once and would likely recognize if it again. A partner that has been informed about but hasn’t experienced it is the bigger risk if it happens 4 years from now during a LIFR departure. Same goes for a new owner if you sell the plane.it seems that OrionFlt has made the best and simplest recommendation. A devoted stand alone static port is a relatively simple solution. I would press Garmin about the  rational for prohibiting use of the ship’s static system.

Edited March 29, 2019 by Shadrach

[smccray]

1 hour ago, Shadrach said:

Does anyone else fly your bird? You’ve been through it once and would likely recognize if it again. A partner that has been informed about but hasn’t experienced it is the bigger risk if it happens 4 years from now during a LIFR departure. Same goes for a new owner if you sell the plane.it seems that OrionFlt has made the best and simplest recommendation. A devoted stand alone static port is a relatively simple solution. I would press Garmin about the  rational for prohibiting use of the ship’s static system.

I’m the only pilot. I’m going to resolve this issue one way or another- I’m not going to leave it as is, but I agree with you that I would recognize a problem easily after having experienced it once.  My wife doesn’t understand why I don’t ground the airplane, but that would be crazy for this issue.

I believe the prohibition against connecting the GSU 25 to the static system is the approval. The parts are experimental approved for certified aircraft under NORSEE. The G3X certified uses a GSU 25d as a PMAd part installed under STC.  The AOA isn’t STCd. I’ve asked Garmin for the PMAd part and the STC, but that isn’t feasible apparently.  NORSEE approved equipment can’t be connected to primary aircraft systems including the static system.

[orionflt]

As i said before give it it's own static port that is not tied into the static system. there is nothing saying you cannot do that. infact the Garmin system requires it's own pitot tube just to keep that portion of the system independent from the aircraft system.

[smccray]

On 3/29/2019 at 7:48 AM, orionflt said:

As i said before give it it's own static port that is not tied into the static system. there is nothing saying you cannot do that. infact the Garmin system requires it's own pitot tube just to keep that portion of the system independent from the aircraft system.

I agree. The fix is straight forward. The issue isn’t the fix, it’s that the limitations aren’t disclosed by Garmin. I want anyone who has a Garmin AOA to know about this limitation. I didn’t know about it, and the warning isn’t included in the manual. 

I also believe the installation is unsafe as prescribed by Garmin.  Garmin says place the static line near the alt static source, not to run a separate static port. We can have differing opinions on the safety of the prescribed installation, but the lack of warning by Garmin is unacceptable.

I believe a compliant Garmin AOA could be a contributing factor in a door opening airplane accident.  The FAA lowered the approval threshold for nonrequired safety enhancing equipment. An open door is an abnormal flight condition- I understand that- but it’s also common and easily addressed with the install. 

[Marauder]

As i said before give it it's own static port that is not tied into the static system. there is nothing saying you cannot do that. infact the Garmin system requires it's own pitot tube just to keep that portion of the system independent from the aircraft system.

How do you go about doing that? I’m sure the location of static ports on airplanes is part of the certification process. Is it as simple as you drilling a hole above the existing one and stick a port in?


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[orionflt]

25 minutes ago, smccray said:

I agree. The fix is straight forward. The issue isn’t the fix, it’s that the limitations aren’t disclosed by Garmin. I want anyone who has a Garmin AOA to know about this limitation. I didn’t know about it, and the warning isn’t included in the manual. 

I also believe the installation is unsafe as prescribed by Garmin.  Garmin says place the static line near the alt static source, not to run a separate static port. We can have differing opinions on the safety of the prescribed installation, but the lack of warning by Garmin is unacceptable.

I believe a compliant Garmin AOA could be a contributing factor in a door opening airplane accident.  The FAA lowered the approval threshold for nonrequired safety enhancing equipment. An open door is an abnormal flight condition- I understand that- but it’s also common and easily addressed with the install. 

truth is, that installation may have little to no issues in a 172 or other aircraft but in the Mooney when the door is opened it creates a negative pressure area in the cabin. that neg pressure is what is causing the issue with the AOA. It is hard for companies putting out products to test every situation in every aircraft they are trying to get their equipment installed in, we saw that last year with Avidyne. you found an issue that is a potential safety problem if the pilot just relies on the AOA to fly the aircraft, the information is definitely a distraction and could cause an inappropriate action but the AOA is not a primary flight aid and is not marketed as such. As much as I agree that putting as much of that info out there would be nice, the fact that it is just an advisory instrument is stated in the operation manual notes and system troubleshooting says to pull the breaker if the system is malfunctioning. 

Brian

[carusoam]

If adding another static port... expect to add them in connected pairs... one on each side of the plane...

We have two for a reason... 

Best regards,

-a-

[smccray]

1 hour ago, carusoam said:

If adding another static port... expect to add them in connected pairs... one on each side of the plane...

We have two for a reason... 

Best regards,

-a-

And that’s the concern- do I put holes in the airframe for this product, or do I punt and go with a different solution that doesn’t have this problem... and doesn’t require holes in the airframe. 

[carusoam]

Things to consider... that come to mind of a PP...

1) Does the AOAi work the way you expect it to.

2) Some people have ultra smooth landings with there AOAi.

3) Can you get more out of it... if you have a complete dual pitot-static system because of it.... that’s pretty nice. 

Best regards,

-a-

[smccray]

14 minutes ago, carusoam said:

Things to consider... that come to mind of a PP...

1) Does the AOAi work the way you expect it to.

2) Some people have ultra smooth landings with there AOAi.

3) Can you get more out of it... if you have a complete dual pitot-static system because of it.... that’s pretty nice. 

Best regards,

-a-

4) would I rather go to the Alpha Systems HUD to get rid of the black box and cord on the glare shield. 

I like the idea of the separate ADHARS in the Garmin system- that’s why I went that direction originally. But if I have to put holes in the airframe I don’t love that idea.

[David foord]

The gsu25 aoa port is required to be connected to the static port if an aoa probe isnt connected.. ie both aoa port and static port on the gsu connected together

 

because something changed when the door opened, id suspect the aoa port is just open to the cabin

[McMooney]

just my opinion, but we cannot engineer out every mode of failure?   Just ignore the aoa/disable as you did until you can sort the situation.

well unless you want that aoa to cost 10x as much and 20x as much to install

 

 

[Pinecone]

Considering people crash due to doors opening on take off or in flight without the added confusion of an AoA system giving the pilot erroneous info, I consider this a BIG deal.

It at least needs to be communicated with pilots.

[Pinecone]

8 hours ago, David foord said:

The gsu25 aoa port is required to be connected to the static port if an aoa probe isnt connected.. ie both aoa port and static port on the gsu connected together

because something changed when the door opened, id suspect the aoa port is just open to the cabin

OP stated that the Garmin installation instructions did not allow the GSU25 to be connected to the aircraft static system.

He is flying A36, so Mooney instructions could be different.

[McMooney]

2 hours ago, Pinecone said:

Considering people crash due to doors opening on take off or in flight without the added confusion of an AoA system giving the pilot erroneous info, I consider this a BIG deal.

It at least needs to be communicated with pilots.

I don't quite understand why someone would let an open door distract them to the point of crashing, atleast in a mooney.  you can't really open it, you aren't gonna fall out, it's just noisy.  you should do as you've been taught, fly the plane worry about the door later.   if the door flies off and gets stuck in the elevator,   aoa will be the last of your worries

it's actually happened to me,  so i do get it.

[McMooney]

1 minute ago, McMooney said:

I don't quite understand why someone would let an open door distract them to the point of crashing, atleast in a mooney.  you can't really open it, you aren't gonna fall out, it's just noisy.  you should do as you've been taught, fly the plane worry about the door later.   if the door flies off and gets stuck in the elevator,   aoa will be the last of your worries

it's actually happened to me,  so i do get it.

now that i think about it, I may be completely wrong but doesn't our alternate static work the same way ?

[Pinecone]

Yes, it should be a no big deal, just fly the airplane.  But not everyone reacts that way.

And yes, our alternate static works that way.  So give it a try, in level flight, pull the alt static and see what happens to Altimeter and Airspeed readings.  Pop the door and see how that effects them.  It is pretty eye opening.

[smccray]

Wow- old thread   I’m still around every once in a while.