Attitude Indicator gone bad

[prestonvanloon]

Any ideas why the attitude indicator is showing 10 degrees pitch up and a slight right roll in straight and level flight and on the ground?

Things I have noticed, but may or may not be relevant:

- Attitude indicator takes a long time to "wake up" on the ground.
- During recent avionics install, several dry rotting vacuum lines were replaced behind the panel.
- The suction gauge is indicating around 5.5" of vacuum pressure at cruise. The green arc on this gauge is around 4.5" and 5".
- Directional gyro works better than before the line replacement.
- The attitude indicator responds correctly to pitch and roll movements. It's just not centered in straight and level flight.
- The last AI overhaul was in 2004
- Sigmatek 5000B-20

Besides replacing the AI and DG entirely with electronic instruments, what are the probable causes and solutions to these issues?

Any recommendations for AI overhaul facilities? 

Edited October 23, 2021 by prestonvanloon

[EricJ]

Sounds like it's wearing out.

[OR75]

I d say 17 years between overhaul is a good amount of time 

[prestonvanloon]

I'm wondering if having too much suction could cause such an issue? The attitude indicator is rated for 4.5" +/- 0.5" and the suction at cruise is 5.5".

[EricJ]

42 minutes ago, prestonvanloon said:

I'm wondering if having too much suction could cause such an issue? The attitude indicator is rated for 4.5" +/- 0.5" and the suction at cruise is 5.5".

Unlikely, but adjusting the vacuum regulator is not difficult.   If you really want to know you could have it adjusted back down.   It may wind up being low on the ground then.

 

[prestonvanloon]

Update: the suction regulator has been adjusted to the correct suction and the attitude indicator is still misbehaving.

A&P troubleshooting soon

[jetdriven]

Pull it and send it to Aircraft wuakity instruments of Wichita Kansas.  

[Ragsf15e]

Options:

1. Aircraft Quality Instruments overhaul 

2. Buy a used one online

3. Install a G5 or GI275

#2, I’d probably only do if you only fly vfr as you’ll have an unknown history on the ADI, but it’s cheap.

#3 is likely most reliable, digital ahrs, possibly get rid of the vacuum system.  Most expensive.

#1 middle of the range for quality and price.

[OR75]

12 hours ago, prestonvanloon said:

Update: the suction regulator has been adjusted to the correct suction and the attitude indicator is still misbehaving.

A&P troubleshooting soon

A&P troubleshooting is a waste a time …. Overhaul or replacement is due 

[prestonvanloon]

1 hour ago, OR75 said:

A&P troubleshooting is a waste a time …. Overhaul or replacement is due 

This could help determine that the AI is, in fact, the problem. If we can swap out the AI for a known working one and that behaves properly then we know it's the AI and not further in the vacuum system.

Overhaul seems like the most viable option. Dual G5s would be nice though...

[N201MKTurbo]

Send it out.

you have to cut the instrument shop guys a little slack these days.

I was talking to the owner of the local instrument shop the other day. He said the replacement gyro capsules they are getting these days are all crap. They have to do the overhaul two or three times to get a good one. All the old timers that knew how to build these things are dying or retiring and the new guys don’t know what they are doing. 

[OR75]

2 hours ago, prestonvanloon said:

This could help determine that the AI is, in fact, the problem. If we can swap out the AI for a known working one and that behaves properly then we know it's the AI and not further in the vacuum system.

Overhaul seems like the most viable option. Dual G5s would be nice though...

Vacuum is …. Vacuum and you adjusted it so what else can be wrong with the vacuum ? 
A&P cannot overhaul an AI , so maybe what he/she can do is hit it a bit and see if it straighten it …. but then how confident will you be behind that ? 

[prestonvanloon]

Problem solved! Spoiler: It wasn't the attitude indicator. 

I followed the advice of many here to go forward with an overhaul. I called AQI, ordered an exchange gyro, and told the mechanic to hold off on any troubleshooting until the new gyro arrived. The mechanic was under the panel for about 2 minutes before he said "you gotta see this" (see picture below). The avionics shop that replaced the vacuum lines zip tied the line so tight that it was crushed. We clipped 3 or 4 zip ties off and everything was back to operational. I'll return the instrument back to AQI for a refund since the AI is working properly again. The shop that completed the vacuum line replacement and zip ties was Forge Flightworks (previously known as Carpenter Avionics) at MQY.

We're skeptical that the previous shop used the correct vacuum hose as well. These clear tubes don't look right. Any thoughts?

 

Edited November 16, 2021 by prestonvanloon

[EricJ]

Yeah, there's a lot that doesn't look right about that.       Glad you found it!

 

[Vance Harral]

3 hours ago, prestonvanloon said:

These clear tubes don't look right. Any thoughts?

While Stratoflex may be the gold standard, I'm unaware of any guidance or regulation which prohibits the use of clear polyethylene tubing in the vacuum system.  Almost all the tubing in our vacuum system is clear polyethylene, some of it installed by multiple shops I trust.

That said, polyethylene tubing doesn't turn yellow overnight, and the hoses in your pic look significantly yellowed.  When poly tubing gets old, it both turns yellow, and also gets brittle, possibly introducing debris into the system.  So even though you've solved your original problem, I'd recommend replacing that tubing next time you're in there.  If it were me, I'd just replace it with fresh poly tubing, rather than the more expensive Stratoflex.

[jamesm]

I have one out of  '67C  if interested.

James '67C

[OR75]

when were those vacuum lines  replaced and zip tied by Forge ? looks like work that was done decades ago based on the color of the poly-tubing and the type of zip ties  

[47U]

20 hours ago, prestonvanloon said:

We're skeptical that the previous shop used the correct vacuum hose as well. These clear tubes don't look right. Any thoughts?

Aircraft Spruce has links to the TCDS for both Tygon and Polyurethane tubing.  The 3/8” ID tubing with 1/8” and 3/16” wall thicknesses are rated in the 25-30” vacuum range.  Bend radius is listed, too.  A little cheaper than -193 hose, although I don’t know what the service life is in comparison.  I know traditional vacuum hose can look fine externally and leak like a sieve, but poly tubing, maybe not so much?

Regardless, glad your AI issue wasn’t anything more serious.

[prestonvanloon]

1 hour ago, OR75 said:

when were those vacuum lines  replaced and zip tied by Forge ? looks like work that was done decades ago based on the color of the poly-tubing and the type of zip ties  

17 hours ago, Vance Harral said:

While Stratoflex may be the gold standard, I'm unaware of any guidance or regulation which prohibits the use of clear polyethylene tubing in the vacuum system.  Almost all the tubing in our vacuum system is clear polyethylene, some of it installed by multiple shops I trust.

That said, polyethylene tubing doesn't turn yellow overnight, and the hoses in your pic look significantly yellowed.  When poly tubing gets old, it both turns yellow, and also gets brittle, possibly introducing debris into the system.  So even though you've solved your original problem, I'd recommend replacing that tubing next time you're in there.  If it were me, I'd just replace it with fresh poly tubing, rather than the more expensive Stratoflex.

Yes, I think that Forge replaced the black vacuum line in the back and then zip tied the existing polyethylene tubing.They mentioned lines were dry rotting and debris falling off at the touch. I think the lines they replaced were to the PC wing leveler system. I'm not sure what they did there, but the wing leveler would not turn off and ultimately had to be disconnected. 

I think we'll replace the yellow tubing in next annual. 

[Vance Harral]

2 hours ago, prestonvanloon said:

I'm not sure what they did there, but the wing leveler would not turn off and ultimately had to be disconnected. 

It'd be a shame to not make use of a functioning wing leveler just because the disconnect mechanism isn't working.

When you say the wing leveler "would not turn off", I assume you're talking about the red, yoke-mounted PC defeat switch?  If so, in the mid-70s vintage Mooneys that is an electrical switch which connects to a vacuum solenoid behind the instrument panel, that opens the PC system to ambient air.  It's pretty straightforward to test, might be as simple as a broken wire that just needs to be reconnected.  If the yoke-mounted switch itself is bad, it's not too awful to replace, and it's a standard electrical switch that can be obtained from Mouser, Digikey, etc.  If the vacuum solenoid is bad, replacements are hard to come by, but they can be gray-market overhauled.  Its just a solenoid attached to a Schrader valve.

[OR75]

13 hours ago, prestonvanloon said:

Yes, I think that Forge replaced the black vacuum line in the back and then zip tied the existing polyethylene tubing.They mentioned lines were dry rotting and debris falling off at the touch. I think the lines they replaced were to the PC wing leveler system. I'm not sure what they did there, but the wing leveler would not turn off and ultimately had to be disconnected. 

I think we'll replace the yellow tubing in next annual. 

So they replaced the lines that were rotting with poly tubing that they picked up from the airport dumpster ? Obviously those yellowed polytubing have seen decades of service already 

[Bob Weber]

I would wager the poly tubing is original and whoever tied the collapsed tubing is at fault.

Vacuum flowing thru a gyro relies on volume and those tyraps inhibited the flow.

When the gyro issue began is probably right after they were pulled so tight.

What is that filter mounted to?

 

Bob Weber

WebAirConsulting.com