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On 11/9/2018 at 2:21 PM, N201MKTurbo said:

BTW,

You don't need the muffler overhauled. Any A&P is legal to weld it. I would find an an aviation welder and just have him fix the crack. As an A&P I would just find a good TIG welder and supervise him doing it. Shouldn't be more than $100 or so, or a few beers if you know them well enough...

I thought all repair on aircraft pats/components required an approved procedure to follow. Usually issued by the manufacturer of the part/component. Without the proper procedure to follow how can an A&P do the work?

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22 hours ago, Cruiser said:

I thought all repair on aircraft pats/components required an approved procedure to follow. Usually issued by the manufacturer of the part/component. Without the proper procedure to follow how can an A&P do the work?

An A&P can weld a muffler if they are qualified to do so. An owner can provide an A&P with an owner produced part as long as it meets the specs of the original part (and is documented as such).  I spent some time in my youth trading flight time for work at a repair station in the mid-west. Owner produced parts were more common than you might think. In that part of the country almost every male born before about 1985 had some exposure to Ag work and if they had a public school education, had used an arc welder, an Oxyacetylene weld/cutting torch and done some basic sand casting of simple parts in metal shop.  This certainly did not make them capable of producing aircraft parts but it seems to have made them comfortable and competent at finding folks that could assist them in doing so. 

A good and fairly recent read: https://www.aopa.org/news-and-media/all-news/2016/june/pilot/is-repair-a-lost-art

Sending a perfectly repairable muffler out for overhaul is about passing the liability on to someone else, not ensuring a safe, reliable and legal repair. I don't judge an A&P/IA for doing so, the world is a tough place and liability plaintiff lawyers are not concerned with finding truth, they're concerned with assigning and attaching blame to the deepest pockets they can.

Edited by Shadrach
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ALL A&Ps used to be taught how to weld to aviation standards as part of their training. We had to pass a welding test to graduate. A&Ps used to weld items all the time ages ago. Tube structures, exhaust stacks, heat muffs, etc. Most won't do it today. We now have "specialty" shops for tube frame airplanes and mufflers. It was basic A&P work back when. Many airports now have "rules" that say you can't weld in the hangar. Old time A&Ps are turning over in their graves watching this stuff.

Welding used to be done all the time just like doing cylinder work in the hangar with a Sioux valve grinder. We even honed cylinders with portable equipment. Many shops had valve grinders in the shop for cylinder work.

A&Ps also always did magneto repairs right in the shop. They knew how to set egap and point gaps correctly. They could put in condensers and points and coils. It ain't rocket science. Mags have been around since the internal combustion engine was invented. I still do mine and I've had no problems with my mag work on my airplane. Even did dual mags for years and never had any problems. Bendix even published a wall chart on how and what to do for mag repairs. Lots of colorful pictures and directions for A&Ps in the shop. Had one on my wall. Wish I still had it. 

YUP. Old time A&Ps are rolling over in their graves 

Another thing pilots need to,learn is the difference between an A&P and an A&P with an IA authorization. Or- what does an IA authorization allow an A&P to do? But that is for another thread. 

 

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2 hours ago, Shadrach said:

Are you suggesting that an AI is not legally able to determine that a weld has been performed IAW standards acceptable to the administrator?  It's a genuine question. By certified do you mean FAA certified? I don't know of any reg that requires an "aerospace welder", but there's a lot of regs I am unfamiliar with and or interpret differently than some of the more conservative IAs.  I know it's an airplane part, but were talking about a steel can that needs to be cleaned inspected and repaired. The affected area appears to need no more than a 3" bead.  A good MIG guy with a pencil grinder could knock that out in minutes not hours.

Ross, I think Clarence was more referring to safety, than legality.

Scud-running is legal, but not necessarily safe.  Or, more to the point, I'm an IA who hasn't welded anything in about 15 years.  Trust me, you don't want me to weld your muffler, legal or not.

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6 minutes ago, Andy95W said:

Are you suggesting that an AI is not legally able to determine that a weld has been performed IAW standards acceptable to the administrator?

Its classed as a MINOR repair. An IA is not required. Only an A&P and a log book sign off. 

You don't want me to weld it either even though, at one time , I was pretty good at it. 

Its a lose-able skill. Just like flying, use it or lose it. 

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15 minutes ago, Andy95W said:

Ross, I think Clarence was more referring to safety, than legality.

Scud-running is legal, but not necessarily safe.  Or, more to the point, I'm an IA who hasn't welded anything in about 15 years.  Trust me, you don't want me to weld your muffler, legal or not.

No, I don't want someone who is not well practiced and competent welding anything. However, being a competent welder and being competent at determining that a weld has been done IAW 43.13 is not the same thing.  I would most certainly trust you to make that determination.  

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4 minutes ago, cliffy said:

Its classed as a MINOR repair. An IA is not required. Only an A&P and a log book sign off. 

You don't want me to weld it either even though, at one time , I was pretty good at it. 

Its a lose-able skill. Just like flying, use it or lose it. 

The truth is a reputable, local machine shop is likely as able to handle a muffler weld as anyone. Many would likely choose to pass on fear of liability. 

Things get more complicated with more complex turbo exhaust systems.

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4 minutes ago, Shadrach said:

he truth is a reputable, local machine shop is likely as able to handle a muffler weld as anyone. Many would likely choose to pass on fear of liability. 

Things get more complicated with more complex turbo exhaust systems.

Yes to the above. 

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3 hours ago, Cruiser said:

I thought all repair on aircraft pats/components required an approved procedure to follow. Usually issued by the manufacturer of the part/component. Without the proper procedure to follow how can an A&P do the work?

AC 43-13.1b has a whole chapter on weld repairs. It is accepted as an acceptable method.

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The crack, as posted by the OP and a second one that I posted, may just be the  tip of the iceberg.  In my case the flame tubes were also gone. Now, this is an even more controversial discussion.  Is a muffler airworthy once the flame tubes are gone?  I am told that the flame tubes are there to control inconsistent heating of the case which causes warping and cracking.  So, while the crack could rather easily be welded, the question becomes how soon the next one starts?  Do you knowingly put the muffler back on with burned flame tubes?  I’ve been trying to get a reasonable answer on this for a while, but not much luck.  I even thought that one shop was building a muffler without the tube, but could not find them.  Another consideration is that the back of the weld can not be cleaned prior to welding.  This leads to potential contamination which leaves a poor weld that can then just cause the crack to reopen or migrate.  I think it amounts to a judgement call on the overall condition of the exhaust.  If it is low time and most components look good, including the flame tubes, it is likely worth welding.  If you have over 500 hours....or 1000 hours, you may be on borrowed time.  If you are paying to have the exhaust removed and installed, consider the overall cost of pulling it again in a few hundred hours.  Unfortunately, when you send the system out, the sandblasting also thins the metal and usually reveals issues with the risers and tailpipe as well.  

With the number of CO incidents each year, I can understand why IAs take the more cautious route and push for an overhaul.  I feel better about my exhaust, knowing I don’t have to worry about the next crack for a few years...or so I hope.  In the meantime....I’m going to research the damned flame tubes some more.

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9 hours ago, Shadrach said:

Are you suggesting that an AI is not legally able to determine that a weld has been performed IAW standards acceptable to the administrator?  It's a genuine question. By certified do you mean FAA certified? I don't know of any reg that requires an "aerospace welder", but there's a lot of regs I am unfamiliar with and or interpret differently than some of the more conservative IAs.  I know it's an airplane part, but were talking about a steel can that needs to be cleaned inspected and repaired. The affected area appears to need no more than a 3" bead.  A good MIG guy with a pencil grinder could knock that out in minutes not hours.

My comment was to the poster who wanted to know why the shop doing his annual didn’t do the weld themselves(if I read it correctly)

With the number of cases of CO poisoning caused by failure of mufflers, I would send it someone that does this for a living, has the skills, knowledge and training to do it.  No disrespect meant to IA’s out there.

In Canada aviation welding is a specialty and must be completed by a Transport Canada (AMO) Approved Maintenance Organization with a rating for welding.  

Clarence

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15 minutes ago, takair said:

The crack, as posted by the OP and a second one that I posted, may just be the  tip of the iceberg.  In my case the flame tubes were also gone. Now, this is an even more controversial discussion.  Is a muffler airworthy once the flame tubes are gone?  I am told that the flame tubes are there to control inconsistent heating of the case which causes warping and cracking.  So, while the crack could rather easily be welded, the question becomes how soon the next one starts?  Do you knowingly put the muffler back on with burned flame tubes?  I’ve been trying to get a reasonable answer on this for a while, but not much luck.  I even thought that one shop was building a muffler without the tube, but could not find them.  Another consideration is that the back of the weld can not be cleaned prior to welding.  This leads to potential contamination which leaves a poor weld that can then just cause the crack to reopen or migrate.  I think it amounts to a judgement call on the overall condition of the exhaust.  If it is low time and most components look good, including the flame tubes, it is likely worth welding.  If you have over 500 hours....or 1000 hours, you may be on borrowed time.  If you are paying to have the exhaust removed and installed, consider the overall cost of pulling it again in a few hundred hours.  Unfortunately, when you send the system out, the sandblasting also thins the metal and usually reveals issues with the risers and tailpipe as well.  

With the number of CO incidents each year, I can understand why IAs take the more cautious route and push for an overhaul.  I feel better about my exhaust, knowing I don’t have to worry about the next crack for a few years...or so I hope.  In the meantime....I’m going to research the damned flame tubes some more.

If the muffler is designed to have a flame tube and I find it missing during an annual inspection it is getting a repair, overhaul or replacement.  The manufacturer wouldn’t have put it in the design if it wasn’t required, so unless someone has an approval to remove it it’s required.

Clarence

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32 minutes ago, M20Doc said:

My comment was to the poster who wanted to know why the shop doing his annual didn’t do the weld themselves(if I read it correctly)

With the number of cases of CO poisoning caused by failure of mufflers, I would send it someone that does this for a living, has the skills, knowledge and training to do it.  No disrespect meant to IA’s out there.

In Canada aviation welding is a specialty and must be completed by a Transport Canada (AMO) Approved Maintenance Organization with a rating for welding.  

Clarence

Thanks for clarifying Clarence.  So the difference is that in CA th facility performing the weld must be certified as well as the installer as opposed to here where the installer alone has the latitude to make the determination that a repair was done to regulatory standards. 

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I wouldn’t suggest just welding the crack if the rest of the muffler was falling apart. But the origional poster didn’t indicate that there was anything else wrong with the muffler. You need to remove the muffler to weld it. When it is off it is easy to look down the flame tubes and see if thery are falling apart. Also the crack shown didn’t indicate there was any unusual stress on the muffler that would require it to be jigged when welded. 

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3 hours ago, takair said:

The crack, as posted by the OP and a second one that I posted, may just be the  tip of the iceberg.  In my case the flame tubes were also gone. Now, this is an even more controversial discussion.  Is a muffler airworthy once the flame tubes are gone?  I am told that the flame tubes are there to control inconsistent heating of the case which causes warping and cracking.  So, while the crack could rather easily be welded, the question becomes how soon the next one starts?  Do you knowingly put the muffler back on with burned flame tubes?  I’ve been trying to get a reasonable answer on this for a while, but not much luck.  I even thought that one shop was building a muffler without the tube, but could not find them.  Another consideration is that the back of the weld can not be cleaned prior to welding.  This leads to potential contamination which leaves a poor weld that can then just cause the crack to reopen or migrate.  I think it amounts to a judgement call on the overall condition of the exhaust.  If it is low time and most components look good, including the flame tubes, it is likely worth welding.  If you have over 500 hours....or 1000 hours, you may be on borrowed time.  If you are paying to have the exhaust removed and installed, consider the overall cost of pulling it again in a few hundred hours.  Unfortunately, when you send the system out, the sandblasting also thins the metal and usually reveals issues with the risers and tailpipe as well.  

With the number of CO incidents each year, I can understand why IAs take the more cautious route and push for an overhaul.  I feel better about my exhaust, knowing I don’t have to worry about the next crack for a few years...or so I hope.  In the meantime....I’m going to research the damned flame tubes some more.

Reinstalling a muffler with a missing flame tube would not meet the requirement to comply with 43.13. 

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Yves,

I may barely recall this one...

Flame tube... the inside part of the muffler where the hot exhaust first enters... has perforations for airflow (exhaust) distribution...

At about 40years and 5,000 hours my M20C had shed a few parts...the flame tube was one of them...

It probably glows red from the heat each flight for most of the flight... (steel begins to glow above 500°F, EGTs are well above that)

If the tube is broken, exhaust may flow out the break in higher volumes.... giving a blow-torch effect in some direction... if that direction is aimed at the can wall... a hot spot will occur, followed by cooling and heating each flight... call it abnormal uneven heating and cooling... that would stress the can and weaken it at the same time...

It was inspected at each annual.

I don’t recall what the fix was for it...

I was blissfully happy flying with the notion that if you can smell the exhaust, you know you have a CO challenge...

Knowing what we know today... I think I would have gone with the PFS at that point... to go with any CO monitor that was available...

Best regards,

-a-

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Anthony has a pretty good recollection, but I think that most traditional mufflers that have a flame tube, have them at the exit. Power flow has a flame tube at the collector that runs into the input side of the muffler, but I think that is unique to their design. In any case, it acts as a diffuser and helps distribute heat more evenly. Hard to get images because it’s an internal piece.. It is expected to die a slow death. Some aircraft mufflers have had design revisions and are no longer made with flame tubes. However, with regard to this discussion, any muffler returned to service needs to meet its original design specs unless it is being overhauled to new specs with data supporting the changes. There are muffler ADs that require design changes at OH.

Edit: I misread what Anthony was saying. The flame tubes are located where the exhaust exits the downtube and enters the muffler.  I should not post after midnight.

Edited by Shadrach
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7 hours ago, yvesg said:

What is a frickin flame tube? Picture?

Yves

Typical aircraft mufflers are a stainless steel can with 2 smaller metal tubes which pass through the muffler from the exhaust stacks on opposite sides of the engine.  Cylinders 1&2 share one and cylinders 2&4 share one.  These tubes have numerous holes around the circumference and are welded to each end of the muffler.  The holes allow exhaust gasses to pass into the muffler and exit the tail pipe.

Over time these tubes distort from heat and eventually fail, in some cases the failed tube can block the exit port to the tail pipe.  Failure of the flame tubes compromises the strength of the muffler can.  Piper Cherokees have metal hoops on the tail pipe to prevent blockage.

If you look up the tail pipe with a borescope you can see the tubes.

Clarence

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9 hours ago, Bob_Belville said:

I don't think the PFS has flame tubes. If I am correct in that it is a significant factor in the life of a muffler.  

Any PFS that I’ve seen don’t have a muffler and hence no flame tubes.  Cabin heat comes from a shroud wrapped around a collection of tubes before the tail pipe.

Clarence

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1 hour ago, M20Doc said:

Any PFS that I’ve seen don’t have a muffler and hence no flame tubes.  Cabin heat comes from a shroud wrapped around a collection of tubes before the tail pipe.

Clarence

Certainly not a muffler in the traditional sense. What Powerflow calls a muffler (their words not mine) is downstream of the heat exchanger and may or may not have a perforated tube. I have an early PFS muffler for a C177 on a shelf in my hangar and IIRC it is a straight through with no internal baffle of any kind. The current Powerflow exhausts have a replaceable insert (perhaps they are optional) that consists of a wrapped, perforated tube that runs from the collector to the tip of the exhaust.

 

 

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On ‎11‎/‎7‎/‎2018 at 2:43 PM, Oldguy said:

@Jim Peace

Here is the info on the CO detector Dan now uses.

Everyone,

The folks at Sensorcon are willing to pass along a 20% discount to pilots on all of their products.  At checkout use the code below.  

http://sensorcon.com/collections/carbon-monoxide-meters

Discount code: aircraft2017

I'm building a device with CO2 detection plus other functions but after reading this I might just buy one so to be still alive and complete my project!

Do you guys have the basic model ($159)?

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