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AI potentially on the outs....what next


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Hey gang!  I'm a rookie and need some thoughts / expertise from the group.  First the background / current state:  on a recent cross country I noticed my AI indicating about a 5 degree left bank while I was actually wings level.  This persisted for some time and had me strongly considering diverting and landing at a reliable shop, had it been anything other than clear and a million I would have aborted the flight.  The sagging AI continued to sag until I began my decent at which time it corrected itself.  Again on the way home I was lucky enough to have total VFR conditions otherwise I would have flown the airlines.  Since that initial sagging flight it has intermittently sagged again in cruise (she's a VFR only bird right now).

So here's the question for the group: given that I have an AI I don't 100% trust ...what next?  Keep in mind my autopilot is a Century 21.  Thanks for your input!

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Just spray some WD-40 on the AI glass and all your troubles will pass.  

Seriously:  

First, is your vacuum system ok?  If it’s sucking about 5” of Hg that’s not the problem and you need an AI overhaul.  

Second, if you fly actual IMC get a backup Attitude gyro.  They’re cheap now, both used mechanical gyros and newer solid state AHRS units.   

No one flies IMC now with just one AI.   We old guys used to, but we don’t have to any more (me, I have 4 independent AHRS now....)

If you can’t afford a second AI send me a PM and I’ll give you one.  

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Since you currently have a VFR only bird you should only be flying VFR which means you don't have to have the AI. Mine was dying a slow death over the course of about a year. The bearings were noisy on shut down, it would often take 5-10 minutes to stand up, sometimes it would just wobble around for up to 20 minutes. Mine is only a VFR bird as well. I just kept flying her until the AI completely gave up the ghost. Truth be told I took some friends flying for a coastal tour after it was toast and just gyrating and also made a flight from SoCal to Phoenix and back. I did change my typical flight back from AZ where I usually would plan to be over Palm Springs when it is dark to make sure that I was landing in Corona before it got dark because I didn't want to fly at night without it. (Can still legally be done but I have my own requirements).

I would still be flying without it and just placard it but my altimeter decided to start sticking on that flight back from AZ. The AI had to come out to get the altimeter out so I had them both overhauled.

If you want to keep flying it without the AI just placard it inop. 

As Jerry said, if/when you decide to upgrade and turn her into an IFR machine have a backup AI. That is what I will do if/when I go that direction.

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You need the AI for your autopilot, so most of the new solid state AIs are not an option.

The AI has an erecting mechanism which will cure the early onset of a warn out gyro. When the precession exceeds the ability of the erecting mechanism the gyro gets the leans.

Your best option is to get it overhauled.

Your autopilot only requires roll information from the AI. If you can find an AI that has any autopilot output, it should work.

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As someone who lost both AIs in IMC due to a vacuum pump failure, let me tell you its no fun.  I was very fortunate to have a controller really help me one on one to get on the final approach course and land safely at my departure airport.  I immediately put in a G5 and I agree with the others that you need an electronic AI.  A g5 may not drive your legacy autopilot but the Garmin autopilot is probably not too far off.  Does the new Aspen drive your autopilot-  I think it does.  

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Thank you for all the ideas and thoughts.  While new glass units (E5 and G5) are sexy and appealing I don't think they are the right fit for my partners and I given our AP and the necessary add-ons for proper and full functionality.

 

@Jerry 5TJ my first thought was vacuum failure but it turns out not to be the case.  The primary vac is doing its job as is the back up vacuum, both working well and not the culprit.  I'll PM you to discuss further.

@201Mooniac a PM will be headed your way as well.

@jazztheglass The G5 is a great unit.  We kicked around the idea of dual G5's but my understanding is that G5's will not drive the Century 21, could be wrong, but that my current understanding.  Also, your experience of loss of AI's in IMC is harrowing and one I'd rather hear stories about than tell first hand stories about.  I'm glad things worked out well for you and I hope you sent that controller a fine bottle of scotch!

I'll post a panel pic later to show what we're working with.  Thanks again for your thoughts.

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