Should Vac System Stay Or Go?

Buck Rizvi

Buck Rizvi

Pre-takeoff checklist
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BoulderBuck
I'm installing dual Garmin G5's (AI + DG/HSI) in my Cherokee Six, which I plan to use regularly for IFR flight plans.

I'm also installing an Avidyne IFD550 GPS/Nav/Com with AHRS.

Since the G5's don't require vacuum, each have a 4 hour battery backup, and can serve as AI backups for each other...

...should I keep my OLD AI as a backup (along with the engine-driven vacuum pump)?

Keeping the old AI would involve moving it to replace one of two old CDI's (the one without glideslope).

Keeping the old AI seemed like a "no brainer," but more than one person has told me that vacuum pump failure is common. In fact, the vacuum pump failed just prior to the plane's pre-buy inspection.

Do I really need the vacuum-driven AI as a "4th" backup to the second G5 and the IFD550?

I'd love to have one less mechanical achilles heel to be concerned about.

panel.png
 
I kept mine. Of course, I have had an EFIS roll inverted on takeoff about 50 AGL in IMC.
 
What is the cost difference between replacing your toasted vac pump/moving the AI or installing a stand-alone electric backup AI such as a Castleberry or a third stand-alone ahrs like a Sandia or Dynon backup system?

I would value having an additional backup, but I don't trust vacuum systems at all. Ever.
 
I have an electric-spinny-AI backup, but the previous owner didn't get the battery option(MidContinent) so I'm keeping an eye out on ebay to find one with a battery and that will be my backup. Then all the vacuum is going to go when I upgrade and since I already have a full electric backup vacuum pump it should save me quite a bit of weight.
 
Your're doing it wrong in your pic. Don't move the AI to the CDI location, move it to replace the electric TC. Now you're compliant with AC 91-75, as long as the G5s have a slip skid indicator. Otherwise, buy a stand alone ball and stick it in the panel. Done. You're welcome.

I don't like relying on software-calculated attitude presentations, of which all of these MEMS-sensor type AIs rely on. Too consumer grade for my taste. As such, I'll never fly IMC without a mechanical backup (as they actually provide direct attitude indications), since I cannot afford a Ring Laser Gyro in my toy. To each their own.
 
I kept mine after installing the G5. I will keep it after installing the second as well. It was cheap to move the old AI and I had a spot for it (looks like you do as well). Vacuum pumps aren't overly expensive and I like backups. Not sure if anyone in inclement weather has ever said, geez...I have too many backup options. :)

That being said, I can understand why people choose remove their vacuum system with the new technology available.

*Disclaimer: I have to keep my vacuum pumps anyway because they operate my de-ice boots.
 
I am.keeping mine, but I need the AI to drive the AP... but when and if I ever replace the AP , I will probably keep the vacuum system

Sent from my SM-G935V using Tapatalk
 
WannFly said:
I am.keeping mine, but I need the AI to drive the AP... but when and if I ever replace the AP , I will probably keep the vacuum system
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Just get the Garmin G500 TXi and the GAD 43e I mean $20000 is a small price to pay to get rid of a vacuum system.
 
I've heard it said that vacuum sucks.

Dump it if you can.
 
chartbundle said:
Just get the Garmin G500 TXi and the GAD 43e I mean $20000 is a small price to pay to get rid of a vacuum system.
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Yupp, that's my plan.. as soon as I find someone to fund it

Sent from my SM-G935V using Tapatalk
 
hindsight2020 said:
Your're doing it wrong in your pic. Don't move the AI to the CDI location, move it to replace the electric TC. Now you're compliant with AC 91-75, as long as the G5s have a slip skid indicator. Otherwise, buy a stand alone ball and stick it in the panel. Done. You're welcome.

I don't like relying on software-calculated attitude presentations, of which all of these MEMS-sensor type AIs rely on. Too consumer grade for my taste. As such, I'll never fly IMC without a mechanical backup (as they actually provide direct attitude indications), since I cannot afford a Ring Laser Gyro in my toy. To each their own.
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Thanks for the feedback on the pic!

Are you saying I should replace the electric turn coordinator because it keeps the standby AI within the 6-pack and in the pilot’s “field of view?” That’s the only bit I could glean by reading AC 91-75, which makes no mention of CDI’s.

The Garmin G5 AI does indeed have a slip skid indicator.
 
Buck Rizvi said:
Thanks for the feedback on the pic!

Are you saying I should replace the electric turn coordinator because it keeps the standby AI within the 6-pack and in the pilot’s “field of view?” That’s the only bit I could glean by reading AC 91-75, which makes no mention of CDI’s.

The Garmin G5 AI does indeed have a slip skid indicator.
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No, you're missing the point of AC 91-75. The point of that AC is that it allows you to replace a TC with a second AI outright. Otherwise you couldn't get rid of the TC.

My point to you is that since you're doing that [adding a second AI] already via the G5 retrofit, might as well jump on that AC and get rid of the TC and stick your mechanical gyro there. The ball requirement is per the AC, but the G5 has it so you're good to go. In the end, this allows you to not lose a second CDI indicator, which has a much higher panel and avionics value. It is unnecessary for you to lose a second CDI capability because of this swap, again thanks to the allowance this AC affords you.

Congrats on the upgrade. Cherokee six is a simple yet versatile platform. I'd love to have that cabin in my Arrow...actually they call that a Lance lol.
 
hindsight2020 said:
No, you're missing the point of AC 91-75. The point of that AC is that it allows you to replace a TC with a second AI outright. Otherwise you couldn't get rid of the TC.

My point to you is that since you're doing that [adding a second AI] already via the G5 retrofit, might as well jump on that AC and get rid of the TC and stick your mechanical gyro there. The ball requirement is per the AC, but the G5 has it so you're good to go. In the end, this allows you to not lose a second CDI indicator, which has a much higher panel and avionics value. It is unnecessary for you to lose a second CDI capability because of this swap, again thanks to the allowance this AC affords you.

Congrats on the upgrade. Cherokee six is a simple yet versatile platform. I'd love to have that cabin in my Arrow...actually they call that a Lance lol.
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depending on the cofig, OP might not be able to keep the 2nd CDI. I am doing the same install, plane in shop rt now, with GAD 29B and i have to get rid of the mechanical CDI
 
WannFly said:
depending on the cofig, OP might not be able to keep the 2nd CDI. I am doing the same install, plane in shop rt now, with GAD 29B and i have to get rid of the mechanical CDI
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why?
 
hindsight2020 said:
No, you're missing the point of AC 91-75. The point of that AC is that it allows you to replace a TC with a second AI outright. Otherwise you couldn't get rid of the TC.

My point to you is that since you're doing that [adding a second AI] already via the G5 retrofit, might as well jump on that AC and get rid of the TC and stick your mechanical gyro there. The ball requirement is per the AC, but the G5 has it so you're good to go. In the end, this allows you to not lose a second CDI indicator, which has a much higher panel and avionics value. It is unnecessary for you to lose a second CDI capability because of this swap, again thanks to the allowance this AC affords you.

Congrats on the upgrade. Cherokee six is a simple yet versatile platform. I'd love to have that cabin in my Arrow...actually they call that a Lance lol.
Click to expand...

by the way the G5 ADI can either be a replacement for AI (unless it runs AP) OR TC (unless it runs AP), not both with 1 unit. the mechanical AI can be moved to TC location only if it doesn't have flight director (and you are installing the G5 ADI as a replacement for the TC)
 
hindsight2020 said:
My point to you is that since you're doing that [adding a second AI] already via the G5 retrofit, might as well jump on that AC and get rid of the TC and stick your mechanical gyro there. The ball requirement is per the AC, but the G5 has it so you're good to go. In the end, this allows you to not lose a second CDI indicator, which has a much higher panel and avionics value. It is unnecessary for you to lose a second CDI capability because of this swap, again thanks to the allowance this AC affords you.
Click to expand...

That makes a lot of sense. Thanks for your guidance! :)
 
WannFly said:
by the way the G5 ADI can either be a replacement for AI (unless it runs AP) OR TC (unless it runs AP), not both with 1 unit. the mechanical AI can be moved to TC location only if it doesn't have flight director (and you are installing the G5 ADI as a replacement for the TC)
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I'm looking at the service manual for my old AutoControl III autopilot and there's no input from the turn coordinator, just the AI.

AC91-75 only mentions keeping the turn coordinator if it's connected to the autopilot, which mine isn't.

Since I'm installing 2 G5's, the 2nd G5 DG/HSI serves as a backup AI & turn coordinator for the first.

Is there another Garmin or Federal doc dictates the flight director / ap limitation of removing the existing TC? Thanks!
 
Radar Contact said:
I kept mine after installing the G5. I will keep it after installing the second as well. It was cheap to move the old AI and I had a spot for it (looks like you do as well). Vacuum pumps aren't overly expensive and I like backups. Not sure if anyone in inclement weather has ever said, geez...I have too many backup options. :)

That being said, I can understand why people choose remove their vacuum system with the new technology available.

*Disclaimer: I have to keep my vacuum pumps anyway because they operate my de-ice boots.
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This is my situation too. I need it for the boots, but even if I didn't have de-ice I would keep the dual pump vacuum system. But if I owned a single I would dump the vacuum system completely.

To the OP, either keep the electric TC, or replace it with an electric AI. The latter will give you triple redundant attitude with independent AHRS/gyros in each. However, if your Autopilot III is still working you'll probably have to keep the vacuum AI.
 
gasfiltered said:
What is the cost difference between replacing your toasted vac pump/moving the AI or installing a stand-alone electric backup AI such as a Castleberry or a third stand-alone ahrs like a Sandia or Dynon backup system?

I would value having an additional backup, but I don't trust vacuum systems at all. Ever.
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Good point. The vacuum pump was fixed before I purchased the plane, so I assume it's good for a few hundred hours (crossing fingers). The shop has agreed to move the old AI at no additional cost as part of the G5 upgrade. Looks like certified electric AI's are $3K. May be the better long term solution.
 
GRG55 said:
To the OP, either keep the electric TC, or replace it with an electric AI. The latter will give you triple redundant attitude with independent AHRS/gyros in each. However, if your Autopilot III is still working you'll probably have to keep the vacuum AI.
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I do have a working AutoControl III that's driven by the old vacuum AI. I think that's what might force my hand into keeping the vacuum solution as a backup rather than go electric. Will talk all of this over with the shop. Thanks for your help!
 
Buck Rizvi said:
I'm looking at the service manual for my old AutoControl III autopilot and there's no input from the turn coordinator, just the AI.

AC91-75 only mentions keeping the turn coordinator if it's connected to the autopilot, which mine isn't.

Since I'm installing 2 G5's, the 2nd G5 DG/HSI serves as a backup AI & turn coordinator for the first.

Is there another Garmin or Federal doc dictates the flight director / ap limitation of removing the existing TC? Thanks!
Click to expand...
If ur TC is not driving the AP (my set up with century 2000) , replacing the TC with the G5 is ur option and move the vacuum AI to TC location. Install manual available on Garmin website had all possible combination listed. The AI can only move to TC position if it doesn't have flight director. I had initially planned to keep the TC as well, but decided not to. With dual G5 and vacuum system there are 3 AI, 2 TC and I am keeping the DG in case the G5 HSI decides to quit. My Gps also has a HSI page.

Sent from my SM-G935V using Tapatalk
 
WannFly said:
If ur TC is not driving the AP (my set up with century 2000) , replacing the TC with the G5 is ur option and move the vacuum AI to TC location. Install manual available on Garmin website had all possible combination listed. The AI can only move to TC position if it doesn't have flight director. I had initially planned to keep the TC as well, but decided not to. With dual G5 and vacuum system there are 3 AI, 2 TC and I am keeping the DG in case the G5 HSI decides to quit. My Gps also has a HSI page.
Click to expand...

Thanks for bringing this to my attention!

I looked up the relevant section of the G5 installation manual and here are the parts that pertain to my situation:

The installation of the G5 requires the retention of the mechanical airspeed indicator, altimeter, and vertical speed indicator.
...
• For installations in aircraft approved for IFR operations:
• If the G5 is installed as the primary attitude indicator, the existing rate of turn indicator must be retained.​
...
• The G5 cannot replace a primary attitude indicator that includes a flight director or is part of an autopilot system (an existing attitude indicator in the primary location that is part of an autopilot but without flight director may be moved to the turn coordinator location and a G5 installed in the primary location)

--------

In my case, my existing AI IS part of the autopilot system (Century III) but does not have a flight director.

That said, it looks like the IFR operations requirements governs here (that's mentioned first), which says I need to keep the existing rate of turn indicator.

Looks like I need to give Garmin a call and go over my options in detail before we execute. Want this to be a "by the book" install!

Thanks! :)
 
You read your last bolded in blue wrong. Since the AP-driving mechanical AI does not have a flight director, it can be moved into the TC position. The part you missed was this: Just because you moved it, does NOT mean the mechanical AI ceased to be your PRIMARY AI.

Get it? You're merely moving your primary-AI to the TC hole and putting your backup-AI in the top center position. Big whoop. It still complies with both the G5 STC (the G5 is NOT your primary, thence you can get rid of the TC) and also complies with the AC in that you have a second AI, which allows the substitution of the TC. Done.
 
hindsight2020 said:
You read your last bolded in blue wrong. Since the AP-driving mechanical AI does not have a flight director, it can be moved into the TC position. The part you missed was this: Just because you moved it, does NOT mean the mechanical AI ceased to be your PRIMARY AI.

Get it? You're merely moving your primary-AI to the TC hole and putting your backup-AI in the top center position. Big whoop. It still complies with both the G5 STC (the G5 is NOT your primary, thence you can get rid of the TC) and also complies with the AC in that you have a second AI, which allows the substitution of the TC. Done.
Click to expand...

Got it. Sometimes I get a little thick in the skull! Thanks for pointing that out! :)
 
I think you're on the right track now keeping your Vacuum AI. I think you now understand you need it to drive you Autocontrol 3, in conjunction with the input from your DG, if it works the same as my Autocontrol 3B in my Archer.
My Aspen drives the DG input for me now, but the G5 with the GAD### interface will work for your AP, but as others have indicated, a G5 cannot be used for the attitude input. Too bad for you and for me with the Aspen.

I relocated my vacuum AI to my top cdi/GS spot and dropped that down to my #2 cdi. I kept my electric TC anyway, not so much as a redundancy, which it was, but because I had years using it for standard rate IFR turns, and of course the ball for coordination.

And look, it's not all bad having separate systems to keep you upright.
 
MajorTurbulence said:
I think you're on the right track now keeping your Vacuum AI. I think you now understand you need it to drive you Autocontrol 3, in conjunction with the input from your DG, if it works the same as my Autocontrol 3B in my Archer.
My Aspen drives the DG input for me now, but the G5 with the GAD### interface will work for your AP, but as others have indicated, a G5 cannot be used for the attitude input. Too bad for you and for me with the Aspen.

I relocated my vacuum AI to my top cdi/GS spot and dropped that down to my #2 cdi. I kept my electric TC anyway, not so much as a redundancy, which it was, but because I had years using it for standard rate IFR turns, and of course the ball for coordination.

And look, it's not all bad having separate systems to keep you upright.
Click to expand...

Thank you! Since the G5 has slip/skid and turn rate (as I’m sure is the same for the Aspen), I think I’m ok with losing the trusty old ball. AC 91-75 says I should know my plane’s appropriate bank angle for a standard rate turn, so it’s the slip-skid info I’ll be missing in the lower left. I agree that it’s tough to beat the ball for that!

I’m curious what all this means if I want to upgrade eventually to the Garmin GFC 500 autopilot? Will check...
 
There is no question that your Autocontrol 3 is long in tooth. However, if it is still working, once you couple the IFD550 to it, if it behaves anything like my Garmin 430w and Aspen to my Autocontrol 3B, the GPSS will amazingly transform your legacy autopilot flying approaches, holds and whatever flight plans programmed.

No doubt the GFC500 autopilot is great, and probably has altitude hold/capture capability, which I believe yours does not. It's cost, and install cost can buy an awful lot of fuel.
 
MajorTurbulence said:
However, if it is still working, once you couple the IFD550 to it, if it behaves anything like my Garmin 430w and Aspen to my Autocontrol 3B, the GPSS will amazingly transform your legacy autopilot flying approaches, holds and whatever flight plans programmed.
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Excellent! I can't wait to put it through its paces!
 
Buck Rizvi said:
Thank you! Since the G5 has slip/skid and turn rate (as I’m sure is the same for the Aspen), I think I’m ok with losing the trusty old ball. AC 91-75 says I should know my plane’s appropriate bank angle for a standard rate turn, so it’s the slip-skid info I’ll be missing in the lower left. I agree that it’s tough to beat the ball for that!

I’m curious what all this means if I want to upgrade eventually to the Garmin GFC 500 autopilot? Will check...
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GFC 500 will work just fine, don't even need the GAD29B adapter that u are installing (I am too)

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Bank angle means very little, possible zero, in an uncoordinated turn.

Your heading in theory could actually be going the opposite direction of bank.
 
WannFly said:
GFC 500 will work just fine, don't even need the GAD29B adapter that u are installing (I am too)
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That’s good to hear. Just listened to aviation news podcast’s coverage of the gfc 500 and I gotta have it! :)
 
Yep, I saw this thread and immediately thought "I bet he needs to keep his vacuum to drive his old ADI which is driving his old AP." And yep, that's what appears to be going on here if I'm reading correctly.

I'm in the same boat. Until an electronic ADI is introduced which a) will drive a Century III AP and b) is allowed to be used as either a primary ADI or backup to the G5, I'm stuck with my vacuum system as are many other owners. You'd think someone would come out with an ADI which has pickoffs for and works with the old attitude-based APs. I'd certainly snap one up just to get rid of my vacuum system.

Now I have two pumps and all kinds of plumbing just to drive one "backup" attitude indicator. Of course in terms of what's legal, it's my primary and my G5 is a backup. Whatever.

When I install my G5s I'm going to remove my second vacuum powered ADI from the right side of the panel. Slowly but surely, old style instruments are going away.
 
Ryan F. said:
I'm in the same boat. Until an electronic ADI is introduced which a) will drive a Century III AP and b) is allowed to be used as either a primary ADI or backup to the G5, I'm stuck with my vacuum system as are many other owners. You'd think someone would come out with an ADI which has pickoffs for and works with the old attitude-based APs. I'd certainly snap one up just to get rid of my vacuum system.
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Misery loves company! ;-)
 
Quick update: Talked it over with my shop. Based on the suggestions here, I'm:

1. Moving the existing AI to the existing Turn Coordinator position. The old AI will remain "primary" and continue to supply attitude reference signal to my AutoControl III autopilot.

2. The Garmin GAD29B will forward nav signal from the Avidyne IFD550 to the old autopilot. The shop says my Piper AutoControl III is essentially a Century II, so the wiring should all work.

3. Will keep both old CDI's (yay). In addition to the Avidyne IFD550, I'm keeping one of my old King KX (with a Mac 1700 front end) nav/com radios for nav/com 2.

4. My shop said they would have an FAA Field Rep sign off on everything, just to make sure we have it right. That's comforting!

Another Cherokee Six Owner recommended the Garmin GFC 500 as an AP upgrade (darn him!). After I digest this upgrade, I think that will be next.

Thanks for all of your help!
 
Buck Rizvi said:
...Another Cherokee Six Owner recommended the Garmin GFC 500 as an AP upgrade (darn him!). After I digest this upgrade, I think that will be next.

Thanks for all of your help!
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Your Cherokee Six owner friend seems anxious to spend your money. ;)
Garmin, on the other hand, is playing hard to get, and thus reluctant to take it. :(

The GFC 500 currently approved for selected models of the 172 and 182 only. Garmin is "working on" supporting installations in the fixed gear, four-cylinder Cherokees only. Only announced plan for the PA-23 is the 301T Turbo-Saratoga it would appear.


https://buy.garmin.com/en-CA/CA/p/604257#additional
 
GRG55 said:
Your Cherokee Six owner friend seems anxious to spend your money. ;)
Garmin, on the other hand, is playing hard to get, and thus reluctant to take it. :(

The GFC 500 currently approved for selected models of the 172 and 182 only. Garmin is "working on" supporting installations in the fixed gear, four-cylinder Cherokees only. Only announced plan for the PA-23 is the 301T Turbo-Saratoga it would appear.


https://buy.garmin.com/en-CA/CA/p/604257#additional
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Scuttlebutt has it...PA 28 181 is very very close

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GRG55 said:
Garmin, on the other hand, is playing hard to get, and thus reluctant to take it.
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I emailed Garmin today and this is what they wrote back:

Hi Buck,

Thank you for reaching out. At this time we do not have any announcements regarding the timeline of upcoming autopilot certifications for the PA-32-300. Your request has been received and we will use this information to evaluate the marketplace for future certification efforts.

For now, I have logged your information into our autopilot interest log and appreciate your note. We do not have a firm schedule at this time. If you sign up for the Garmin Aviation Newsletter (look for “Stay Informed” on the middle-right side of this web page: https://fly.garmin.com/fly-garmin/), you will get pro-active communications on our most recent announcements and plans. Again, we greatly appreciate your direct feedback. If you might have any other questions, please let me know. Thank you!

---

Should I hire a Russian bot-net to swamp them with PA-32-300 requests? ;-)
 
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