AI Plays Dead

[flyboy0681]

On a VFR trip this past weekend the attitude indicator rolled over and played dead for a little while before mysteriously coming back to life.

What brought it to my immediate attention was the plane going into a shallow dive with the KAP-150 set on heading mode only (ALT was not on).

About 12 minutes later the AI started coming back to life and worked perfectly for the rest of the day.

My partner reported this identical situation about three weeks ago and the AI worked fine up until now and we have been watching the situation closely.

I'd like to get some opinions of what the problem may be. Before I get responses about the vacuum pump, be aware that it was replaced about 15 hours ago with a brand new one along with new filters.

 

 

 

[fantom]

Did the old pump fail in flight and leave a pile of carbon residue, and how well were the lines cleaned out before the filters were replaced?

How long since the AI has been overhauled?

[201er]

I've had the same thing happen with my AI. Mech tested vac system since and said it's flawless (no suction gauge on Mooneys to go by). He says I'm going to need the AI overhauled, so looking at about $700 to have that done. I'm trying to hold out till annual cause it takes at least a week. It's been working fine again for a while so keeping fingers crossed. But it would be the instrument I'd trust least if it disagreed.

[John Pleisse]

Quote: flyboy0681

 Before I get responses about the vacuum pump, be aware that it was replaced about 15 hours ago with a brand new one along with new filters.

 

 

 

[Cruiser]

another thing to check is the time since the AI was last overhauled. Failing AIs can show this kind of symptom. The gyro slows down and the indication will tilt. As the gyro slowly comes back up to speed the display will right and work normally. Tempurature in the cabin can effect it as well. Heat sometimes helps.

 

Mike, is yours a KG 258? is so where are you getting OH for $700?

[201er]

Not sure what mine is. My mech checked the model for me and got the quote. It was going to be over 1k for a drop in overhaul replacement so I'd rather wait a week for mine to be overhauled during annual and save $300.

[Cris]

Quote: 201er

I've had the same thing happen with my AI. Mech tested vac system since and said it's flawless (no suction gauge on Mooneys to go by).

[flyboy0681]

I'll collectively answer all your questions. First, the pump was replaced after the first AI failure, which was 2 weeks ago. About two weeks after the first failure the pump made a really weird buzzing noise as I was bringing the power back down to idle. I immediately taxied back to the hangar and called it a day, and our resident A&P, who reported that we needed a new one. The old one lasted about 600 hours.

I seem to recall hearing that the AI was last overhauled shortly before I bought in a year ago and 200 hours on the airframe, but not sure what the hours on it were.

I'm diligent on my checklists and the vacuum gauge is always in the green.

 

[jetdriven]

my Dr has a Ki-256 like yours in a Bonanza and his did that a few times. he flew up to Autopilots Central and told them he wasn't leaving until they fixed it. Turns out a gimbal bearing was bad andit would occasionally bind.  They went all through it, unsure it it was a repair or overhaul, either way.  It was fixed.  The KI-256 is an expensive unit to overhaul. 

[201er]

Quote: Cris

Mike- Don't you have a high/low vac indicator in your annunciator panal? MORE TO THE POINT HAS IT BEEN TESTED? If you have the AI overhauled your mechanic can add at very little cost a simple 1" suction guage to your panal like many of the latter Mooney's. A better idea is a low cost back up http://www.thevacsource.com/svs.php system which includes the warning now that you will be regularly "in the clouds"   

[flyboy0681]

Well folks, after $2100 in repairs the unit is back in the panel.

 

Nuff said.

[201er]

Ouch! Isn't that close to what it's worth brand new?

[pjsny78]

for what its worth i just sent my AI to be overhauled and its all set for me to pick up and installed back in the plane. i owe $1,200 to the avionics shop in CT. they have a great reputation.

[flyboy0681]

Quote: 201er

Ouch! Isn't that close to what it's worth brand new?

[Cruiser]

Mid Continent quoted $2,400 for overhaul of my KG258, local shops were less. The best quote was $1,100. I decided to put that money into my new Aspen install.

Lapeer Aviation did the work and I cannot say enough good things about this shop. The work is first class. We will be calibrating and flight testing today.

[PTK]

Has anyone ever tried Bob Bramble, at Aerolab Aviation Services? My understanding is that he was performing precisely this kind of work at Bendix King and thus intimately familiar with the King AI's and HSI's. Very reasonable too.

 

[flyboy0681]

Quote: allsmiles

Has anyone ever tried Bob Bramble, at Aerolab Aviation Services? My understanding is that he was performing precisely this kind of work at Bendix King and thus intimately familiar with the King AI's and HSI's. Very reasonable too.

 

[jetdriven]

Aircraft quality instruments in Wichita is a good shop.  I have two of their gyros now.