FAA ACS on Turbo V-Band couplings

[DVA]

Hi all,

Thought I’d make sure this was front and center, forgive me if this is a repost.

TL;DR
The FAA is requesting input on the inspection and condition of turbocharger v-band couplings (of all types, on all aircraft, and all engine types) due to the continued in-flight failures seen despite the numerous ADs and corrective guidance. If your plane has couplings that look similar this, please be extra vigilant with your inspections. While the ACS speaks mainly about the large turbo-exit exhaust coupling, any of the v-bands can and have failed. Click here for the ACS.

[Zwaustin]

About 350 a pop installed on a tsio360lb and there are two.... must be a really special clamp!

[N201MKTurbo]

Made from the finest stainless steel! The spot welds were done by true artisans. The machine work on the threads is superb. A finer clamp cannot be found Anywhere!  

[carusoam]

This is a multi part challenge...

And not doing it properly can and has ended up poorly.

1) These exhaust clamps are expensive.

2) They Have limitations on being re-used.  (Edit after DVA's input, below...)

3) When they get re-used, they are susceptible to failing and leakage. Leakage at the the turbocharger is similar to having a blow torch operating under the cowling.  This is a set-up for an inflight fire with loss of power.

4) Some mechanics don't know the issue regarding re-use of these clamps.

5) Some other maintenance is aided by first removing the exhaust clamps for better access. This is a set-up for the owner/pilot to not even think the exhaust clamps may have been re-used.

This is a PP thought on what I have learned about exhaust clamps and thinned exhaust tubing over time. Somebody has posted some nice photos around here of their exhaust system issues on their Bravo...

Does Continental use the same V-clamps?

Best regards,

-a-

[DVA]

2) They can't be re-used.
3) When they get re-used, they are susceptible to failing and leaking
Does Continental use the same V-clamps?
Best regards,
-a-

The service bulletin, Lycoming and the OEM sheet says they can torqued twice.

Yes on the Continental.

[carqwik]

This is the May 2016 accident referred to in the ACS:

https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20160516X05929&key=1

Beech A36TC with Continental engine.

[BobAustin]

Yes that accident in Tupelo MS was my neighbor at Kerrville (60TE) Jack Jackson and Gyen his wife along with another couple.  I have encouraged everyone with a Continental turbo to not reuse that clamp over 3 times.  Big discussion on Beechtalk.  The TN conversion has bracket to prevent the part from falling off and starting a fire.

[carusoam]

Additional thoughts...

(1) The first clamps (closer to the engine) are under the most temperature and pressure. A leak at this point will have the highest level of impact as the full pressure and temperature exhaust gasses will be escaping.

(2) The usual grab and tug on the tail pipe is a bit removed from the pipe on the other end of the TC or TN.

(3) reminds me of the space shuttle with a leaky Oring seal with a random blow torch effect....

4) What are the thoughts to identify the issue on departure,  and how to handle the fire (usual shut down in case of Fire routine?)

Keep spreading the word...

Best regards,

-a-

[N201MKTurbo]

Does anybody know how the clamps fail? Does the bolt break, the spot welds fail or the band itself cracks.

[takair]

1 hour ago, N201MKTurbo said:

Does anybody know how the clamps fail? Does the bolt break, the spot welds fail or the band itself cracks.

As I recall, they can start to crack around the inner circumference where they are difficult to detect.  Once the crack progresses and the leaking starts, all bets are off.  I suspect that the metellurgical characteristics are degraded from optimal due to the constant heating and cooling cycles, this likely affects the ability to get safe torque and seating after some amount of reuse.

[DVA]

1 hour ago, N201MKTurbo said:

Does anybody know how the clamps fail? Does the bolt break, the spot welds fail or the band itself cracks.

There are numerous ADs out on these on different aircraft; the Twin Cessna’s have a bunch of them. There are a few ways I’ve seen and heard these fail:

• Improper installation of the V-Band - you just don’t tighten them down and go on. They have a procedure that must be followed, here is the Lycoming SI as an example.
  • If it is improperly installed it can work loose as the heating and cooling cause expansion and contraction.
  • People tend to way over torque these because 70-90 in-lbs “just doesn’t feel right” - that would be a wrong assumption.
• Improper installation of the exhaust headers - there are slip joints that must slip to allow for expansion and contraction of the entire exhaust assembly.
  • Failure to ensure that the entire exhaust assembly is settled naturally in place can cause stiffness and tension resulting in damage
  • Liberal use of Mouse Milk or other penetrating high temp lubricants should be used.
• Failure to safely wire. These must be safety wired so if the bolt breaks or loosens the coupler stays on: see the pic from my M20M below
• Long periods of excessive heat. Temps past 1750dF (not 1650dF) - in other words, improper operation. (the difference between 1600df and 1650 won’t change a thing, but I’m not going to try poke that dog :-)
• Design defects in some models. Old V-bands designs required replacement, here is the NTSB report from a long time ago that is still valid today
• Use of the same coupler more than twice - the SI and other instructions warn against this. Who knows if it has validity.
• Not replacing the equally expansive gasket at the same time as the coupler.
• Then this - failure to identify a looming issue by looking for the signs and symptoms of impending doom.

The failure to properly inspect this area of the engine (and other engine things) on a regular basis - instead waiting for the annual to “find issues”.  I bet (no data, just gut) that the majority of these V-Band failures - save the defective recalled parts - are caused by one of the of the above.

For those who know me I preach owner maintenance. I think every owner should learn to remove and replace the cowling. Even if you don’t have the desire to do oil changes or other authorized owner stuff, you should learn what to look for and inspect the entire engine area often. I do it every 25 hours at the oil change and whenever I see or hear something out of the norm. That’s how I caught the second picture below, well before I could have had a big problem.  Your A&P can show you how to remove and re-install the cowl, and can go over things for you to look for, such as what an exhaust leak looks like, how to use your hands to check for parts that should and should not wiggle, rubbing wires or cables, loose stuff, oil drips, and a host of other neat things.

Doing this one simple thing - inspecting under the cowling - can save you time, money and maybe your butt.

[N201MKTurbo]

3 hours ago, takair said:

As I recall, they can start to crack around the inner circumference where they are difficult to detect.  Once the crack progresses and the leaking starts, all bets are off.  I suspect that the metellurgical characteristics are degraded from optimal due to the constant heating and cooling cycles, this likely affects the ability to get safe torque and seating after some amount of reuse.

Kind of a tough deal. The best way to inspect them would be to take them off, but they are saying that you can't do that. It is hard to imagine that gently removing and replacing the clamp would stress it more than heating it to cherry red and cooling it thousands of times.  

[larryb]

So there is a lot of evidence that this part is a problem. Why can't they design a better one? It really should not be hard to design a clamp that would never fail.

[takair]

4 minutes ago, N201MKTurbo said:

Kind of a tough deal. The best way to inspect them would be to take them off, but they are saying that you can't do that. It is hard to imagine that gently removing and replacing the clamp would stress it more than heating it to cherry red and cooling it thousands of times.  

I agree, but it can be difficult to get it back on exactly as it came off.  The exhaust and flanges warp slightly and the clamp is trying to pull it back together.  If it has the right amount of malleability then it may be ok, but as the clamp becomes embrittled it may be a set up for cracking.  Not a metallurgical engineer......so I could have it all wrong.

[N201MKTurbo]

I just looked on line and clamps for RaJay turbos are available from the racing world for $23. They look identical... Oh well....

[N231BN]

Does anybody know how the clamps fail? Does the bolt break, the spot welds fail or the band itself cracks.

I found a broken clamp on my 231 last year, it was the bolt. Safety wire was all that was holding the tailpipe on.

[Danb]

These are great posts especially for someone like me, while I do my own oil changes with help from my friend who has a Bo and is mechanically inclined I'm not, its another item I can look for, without these quality posts I'd have no clue what I'm looking for/at.

[N231BN]

Weird thing is I didn't notice it until I removed the turbo to replace the #3 cylinder. The safety wire held everything tight so the bolt wouldn't wiggle even though it was sheared.

[DVA]

Weird thing is I didn't notice it until I removed the turbo to replace the #3 cylinder. The safety wire held everything tight so the bolt wouldn't wiggle even though it was sheared.

According to an A&P friend of mine who has been in the biz for nearly 40 years "you should see how many of those vbands that I see with no safety wire."

[N231BN]

According to an A&P friend of mine who has been in the biz for nearly 40 years "you should see how many of those vbands that I see with no safety wire."

I don't remember seeing them safety wired on any of the twin Cessna's I worked on years ago.

[N201MKTurbo]

I just looked some more on line and a company called RaJay parts has the RJ0193 clamp for $78 it is PMA and should work on my installation and on 231s. They have the gaskets too. They are kind of hard to find, I'm down to my last set.

[peevee]

Oh great, another part that should cost ten bucks that can fail and kill me. I'll add it to the list. 

[Emmet]

1 hour ago, N201MKTurbo said:

I just looked some more on line and a company called RaJay parts has the RJ0193 clamp for $78 it is PMA and should work on my installation and on 231s. They have the gaskets too. They are kind of hard to find, I'm down to my last set.

That sounds interesting. I paid 299 each the last time. Where did you find a reference that those are the #633358 equivalent?

[N201MKTurbo]

2 hours ago, Emmet said:

That sounds interesting. I paid 299 each the last time. Where did you find a reference that those are the #633358 equivalent?

I didn't. It is a RaJay turbo and it is the RaJay clamp. I believe it is the specified clamp for my installation. Even though they are the exact same turbo, Continental probably sticks a different part number on it and marks it up 400%.

[thinwing]

These clamps are the reason I do every oil change at 25/30 hrs ..it's a mini annual every time and every slip joint gets painted with mouse milk including these turbo vclamps.Also the wastegate pivot shaft gets it and checked for freedom of movement.All exaust risers/stubs get checked for blowby than every flight its check that aft exaust connection ....