FAA Safety Briefing: Exhaust System and increased fatalities

RyanB

RyanB

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A recent FAA Safety Briefing has been released on the subject of the exhaust systems found in general aviation and the increasing number of injuries and fatalities from their failure.

The article seems to imply the only way to truly determine if your exhaust system is up to par, is to remove it and visually inspect the inside. Is an external inspection really not sufficient in determining the health of the exhaust manifold?

What do we make of this?

Article - https://medium.com/faa/aircraft-mufflers-the-hidden-danger-you-need-to-know-eee7d57f3ef0
 
Years of neglected maintenance, and owners waiting on it to fail before doing anything about it.
 
Since the planes must undergo annual inspection, why is this an owner neglect issue?
 
Doc Holliday said:
Years of neglected maintenance, and owners waiting on it to fail before doing anything about it.
Click to expand...

What maintenance is being neglected? Are there SBs or ADs that specify remove and inspect the exhaust system?

'waiting on it to fail before doing anything about it'... about what? A piece of hardware that is causing no symptoms? Better pull all those jugs every 10 hours because something bad might be afoot!!!

One of the worst things you can do is simply take parts off 'because' as that introduces human factors/MX errors.

I did read about 'scoping the muffler, that may be enough but some mufflers have fairly complex baffle systems that would prohibit detailed inspection.
 
Clip4 said:
Since the planes must undergo annual inspection, why is this an owner neglect issue?
Click to expand...

Removing and inspecting the muffler/exhaust is not part of the Part 43 Appendix D annual.

"(8) Exhaust stacks - for cracks, defects, and improper attachment." this is an external, visual inspection and doesn't cover the muffler.

The FAA is worried about internal issues like obstructions and improper manufacture... things that require taking parts off.

“What we’re finding is wear and damage on the inside of the exhaust system. The muffler may be failing in a way that’s not readily visible to a pilot or a mechanic who’s only looking on the outside,” he explains.
 
pfarber said:
What maintenance is being neglected? Are there SBs or ADs that specify remove and inspect the exhaust system?

'waiting on it to fail before doing anything about it'... about what? A piece of hardware that is causing no symptoms? Better pull all those jugs every 10 hours because something bad might be afoot!!!

One of the worst things you can do is simply take parts off 'because' as that introduces human factors/MX errors.

I did read about 'scoping the muffler, that may be enough but some mufflers have fairly complex baffle systems that would prohibit detailed inspection.
Click to expand...

Swing and a miss. ;)

When owners are seeking out signature sellers to perform the 20 minute annual, nothing gets looked at.

I’ve performed annual inspections on planes I haven’t previously worked on to find loose clamps, broken bolts and exhaust gaskets leaking or partially blown out. I’ve removed muffler shrouds to find holes in the muffler. Yep, supposedly the previous guy checked all of this on his inspections. :rolleyes:

Oh, and how many times have I seen JB Weld used to “patch” a muffler shroud, or better yet, the blue exhaust RTV used on exhaust riser gaskets because the flange was barely there anymore.
 
Defects can develop post Annual.

I’m a firm believer in CO Detectors.

Any better than none.

I check the Exhaust System by pressuring with a Leaf Blower and soapy water at Annuals.

It will detect leaks far better than visual with minimum disassembly.

Suggest Owners do this pre-winter too.

All it takes is one little oops during a mag check to create a killer.
 
Obviously it's important. I think any pilot is foolish not to carry a CO detector in planes with exhaust heaters. It's impossible to predict cracks. One of the club planes set off the co monitor last winter just a couple weeks out of annual, at which time the exhaust was pressure tested. The guy flying said he couldn't smell anything; the co detector was the only indication there was a problem.
 
Since 1990 Canada has had an AD that applies to every airplane that uses the exhaust system as a source of cabin heat. It demands that the heat shroud(called a "muff" by some) be removed and the muffler or exhaust pipe be closely inspected with a magnifier for cracks, pinholes and so on. Any suspect areas are examined more closely, and pressure testing (air provided by a vacuum cleaner outlet sort of air pressure) put on the system and the areas covered with soapy water to look for bubbles. I found enough failing parts like that. Sometimes there was leakage without any visible indication on the surface to suggest it. The shroud itself is checked for soot or exhaust stains.

I did the pressure test every time. It was a much better way of ensuring that the component was safe. And the assertion by some: "One of the worst things you can do is simply take parts off 'because' as that introduces human factors/MX errors" is so bogus it's not funny. Not considering the numerous leaking mufflers and stacks I found in my career. Carbon monoxide in the cabin is just as about deadly as flying into the side of a mountain.

https://tc.canada.ca/en/aviation/re...-civil-aviation-safety-alerts-casa-no-2019-07
 
Doc Holliday said:
Swing and a miss. ;)

When owners are seeking out signature sellers to perform the 20 minute annual, nothing gets looked at.

I’ve performed annual inspections on planes I haven’t previously worked on to find loose clamps, broken bolts and exhaust gaskets leaking or partially blown out. I’ve removed muffler shrouds to find holes in the muffler. Yep, supposedly the previous guy checked all of this on his inspections. :rolleyes:

Oh, and how many times have I seen JB Weld used to “patch” a muffler shroud, or better yet, the blue exhaust RTV used on exhaust riser gaskets because the flange was barely there anymore.
Click to expand...

If an owner installed a brand new exhaust system within the preceding 12, removal for inspection is a waste. So I’ll ask again. What is the time standard before the exhaust needs to be removed for inspection?
 
Clip4 said:
If an owner installed a brand new exhaust system within the preceding 12, removal for inspection is a waste. So I’ll ask again. What is the time standard before the exhaust needs to be removed for inspection?
Click to expand...
I have found exhaust stacks in 172s cracked less than 100 hours after being replaced with new. It happens. The Canadian AD stipulates every year or 150 hours, whichever comes first.

Moreover, if a pilot is doing the runup and inadvertently switches to OFF and then back on again, that big bang puts terrific stress on the muffler and the rest of the exhaust system. It can start cracks. One has to remember that at high power settings that system gets red-hot. It's amazing that it doesn't fail more frequently.

A shop across from us was doing the AD inspection on a Cherokee. The mechanic took the shroud off and found a hole in the muffler he could put his fist into. "No wonder I was getting headaches," the owner said. He had bought the airplane a few months earlier and hadn't used the cabin heat yet. Might not be alive now if he had. When they took the muffler off it fell apart in two pieces. The AD inspection had been signed off as having been done at the previous annual, maybe 40 hours before. Yeah. Right. Sure it was.
 
Clip4 said:
If an owner installed a brand new exhaust system within the preceding 12, removal for inspection is a waste. So I’ll ask again. What is the time standard before the exhaust needs to be removed for inspection?
Click to expand...

Pay attention to the discussion.

Where was it brought up about a new system that was installed in the previous 12 months???

Secondly, do you know the difference between "inspection" and "removal for inspection"? .

Here's an example from a Piper PA28 Archer MM

The entire exhaust system, including heat exchange shroud, muffler, muffler baffles, stacks, and all
exhaust connections must be rigidly inspected at each l00 hour inspection. The possibility of exhaust system
failure increases with time-in-service. Check more carefully as time-in-service on the installed muffler increases.
The system must be checked carefully before winter operation when cabin heat is in use. Refer to Figure 78-1
for the Archer II exhaust system. Figure 78-2 depicts the Archer III exhaust system.
Remove the tail pipe and stacks for muffler baffle inspection. Remove or loosen all exhaust shields, carburetor
and cabin heat muffs, shrouds, heat blankets, etc., as required for complete system inspection. Perform cleaning
operations and inspect all external surfaces for dents, cracks, and missing parts.

Pay particular attention to welds, clamps, supports, support attachment lugs, slip joints, stack flanges, and
gaskets. Inspect internal baffles or diffusers. Any cracks, warpage, or severe oxidation are cause for muffler
replacement.

If any component is inaccessible for visual inspection, do the following:
l. Do submerged pressure check of muffler and exhaust stack at 2 psi air pressure.
2. Ground test using carbon monoxide indicator by heading airplane into wind, warming engine on
ground, advancing throttle to full static rpm with cabin heat valves open, and taking readings of heated
airstream inside cabin at each outlet (including rear seat heat outlet, if installed). If carbon monoxide
concentration exceeds 0.005 percent or if a dangerous reading is on an indicator not calibrated in per-
centages, muffler must be replaced

archer.JPG archer 3.JPG


Also, we have

Appendix D to Part 43 - Scope and Detail of Items (as Applicable to the Particular Aircraft) To Be Included in Annual and 100-Hour Inspections

(d) (8) Exhaust stacks - for cracks, defects, and improper attachment.

(10) All systems - for improper installation, poor general condition, defects, and insecure attachment.
 
As I mentioned in my post, except the Piper SB, I was aware of the SB. Also Pipers are very prone to exhaust damage when the mag is switched off then on during runup. Every hundred hours on a most Cessnas would be absurd.
 
Clip4 said:
As I mentioned in my post, except the Piper SB, I was aware of the SB. Also Pipers are very prone to exhaust damage when the mag is switched off then on during runup. Every hundred hours on a most Cessnas would be absurd.
Click to expand...
That Piper SB is asking for a pretty thorough sort of inspection. That's because that system has a history, not because Piper is a bunch of jerks.

Cessna's inspection sheets call for an inspection of the induction and exhaust systems every 50 hours. That's every oil change. It doesn't involve taking anything apart. You just have a good look with a flashlight and a mirror. Takes a few minutes. I lost track of the times I found cracked risers or muffler bulkheads or carb heat muffs that way. Cessna wants that cabin heat shroud off every 100 hours and the muffler inspected closely. The Canadian AD supersedes that, at 150 hours. A mechanic who is diligent enough to do it properly knows that it's not unreasonable at all. He finds cracks. He knows how dangerous they can be. Some owners/pilots don't understand the risk and resent the time spent on it. It's their skin in the game here, and they die if it it goes bad in flight. The lazy/dishonest mechanic lives to tell the judge why he didn't bother doing the job right.

I did a prepurchase on a 172 that had had an annual maybe 15 hours prior. I found two of the four exhaust stacks cracked two-thirds of the way around, just under their cylinder flanges, both on the right side of the engine. If they had both let go in flight the muffler would have dropped a bit and let flame out to set stuff afire. Those cracks didn't occur in the previous 15 hours. Nobody was looking for them, that's all.

Exhaust failures in an airplane are far more serious than in your car.
 
Some related items:

Assure that all openings through the Firewall are sealed.

If the Muffler is accessible during Preflight whacking the COLD unit with
your hand and noting clanging that would be indicative of internal failure.

Altering the length of the Stack may have 2 effects.
1, Moving the exhaust gas further from the fuselage is beneficial in
in reducing CO in cabin and external staining.
2. On the other hand ; vibration on longer/altered Stacks
seems to lead to more cracking of the Pressure Can.

Most aircraft have Boots on the Steering Rods that can deteriorate and
allow CO to enter cabin.

Internal Baffles WILL distort and break with Heat and time.
This can dramatically reduce power output.
Installation of a Bail or Guard will only postpone power loss until a more
In depth inspection is accomplished.
 
My exhaust system sits behind about 300 screws that I have to remove before I can look at it. Neglected maintenance! Suck my unmentionables. That said I really think @Bill has the right of it. Sensorcon makes really goo CO monitors, my airplane sports one. They're spendy, but they'll give off an alarm if there's increased CO that'll get through airplane noise and headsets and everything.
 
steingar said:
They're spendy,
Click to expand...
I would describe them as cheap... especially compared to what an a&p charges to remove the cowlings, not to mention the exhaust. I think i paid $120 for mine.

Moving down the risk matrix: priceless.
Risk-Matrix-1024x550-1024x550~2.png
 
Clip4 said:
As I mentioned in my post, except the Piper SB, I was aware of the SB. Also Pipers are very prone to exhaust damage when the mag is switched off then on during runup.
Click to expand...

What I posted was not the SB, but directly from the MM detailing a 100 hour/annual inspection.


Clip4 said:
Every hundred hours on a most Cessnas would be absurd.
Click to expand...

Even though the Cessna MM requires it?

Again, are you even aware of what's required to inspect an exhaust system?
 
So last annual my mechanic found a hole in my exhaust by looking at it via a small mirror (something that looked like came from a nearly dentist office lol) and a light. i would guess other A&P do it the same way without taking the entire thing off, though its not that hard to take it off on Archers i would imagine.

I carry CO detector in winter when i use cabin heat, this was summer when they found the hole.
 
WannFly said:
So last annual my mechanic found a hole in my exhaust by looking at it via a small mirror (something that looked like came from a nearly dentist office lol) and a light. i would guess other A&P do it the same way without taking the entire thing off, though its not that hard to take it off on Archers i would imagine.

I carry CO detector in winter when i use cabin heat, this was summer when they found the hole.
Click to expand...

Look at the valve that activates cabin heat. They are not a completely sealed valve, and they usually leak, especially as they age.

Even in the summer, when not selecting cabin heat, and a muffler is leaking you still can get CO leaking through.
 
Doc Holliday said:
Look at the valve that activates cabin heat. They are not a completely sealed valve, and they usually leak, especially as they age.

Even in the summer, when not selecting cabin heat, and a muffler is leaking you still can get CO leaking through.
Click to expand...
good to know. should start packing the CO detector all year
 
WannFly said:
good to know. should start packing the CO detector all year
Click to expand...
I just adjusted mine the other day. It was about 1/2" open when the lever was on "off". I got it down to about 1/8", but better than that would've required removing it and filing down the corners.

I velcroed my sensorcon to the panel. I found out that I get a fair bit of co during slow flight. I need to figure out how slow I can go before it starts coming in, which is another reason to have an actual monitor. Id hate to pass out over Fisk.
 
What was the most recent accident that the FAA/NTSB contributed to an exhaust system, and how about a simple non-turbo charged accident?

Honest inspection is important but true accidents caused by lacking of exhaust system maintenance must be an extremely small number.
 
bnt83 said:
Honest inspection is important but true accidents caused by lacking of exhaust system maintenance must be an extremely small number.
Click to expand...
Yup. Not a big number. But not zero, either. Just one more thing (out of many) that can get you if you're determined to keep getting $200 annuals.
 
Magman said:
2. On the other hand ; vibration on longer/altered Stacks
seems to lead to more cracking of the Pressure Can.
Click to expand...
A friend of a friend died that way. There are now STCs to do it the right way.
 
Jim K said:
I would describe them as cheap... especially compared to what an a&p charges to remove the cowlings, not to mention the exhaust. I think i paid $120 for mine.
Click to expand...

If you did that once it would be cheap. But you'll be doing that every two years. That's how long they last.
 
I was under the impression they could be recalibrated with a life limit of 5 years. I haven't had mine 2 years yet, so i haven't crossed that bridge.
 
bnt83 said:
What was the most recent accident that the FAA/NTSB contributed to an exhaust system, and how about a simple non-turbo charged accident?

Honest inspection is important but true accidents caused by lacking of exhaust system maintenance must be an extremely small number.
Click to expand...
I knew a pilot that died because of exhaust issues. He had a cfi with him as well. I didn’t know the cfi. It was a new exhaust system installed due to a pending sale of the aircraft. I guess the mechanic missed something along the way.
 
There are components that can play a role in Exhaust System failures as well.

QUOTE="Dan Thomas, post: 3106456, member: 4817"]A friend of a friend died that way. There are now STCs to do it the right way.[/QUOTE]

There are folks that believe things are done “ the right way”.

Let’s hope it really is done properly.


The Colt has a brace on the Stack that looks right out of the Parts Manual.

It is secured very well but TO THE ENGINE MOUNT!

So now you have an Engine shaking around being sort of restrained by means

of the Exhaust Stack!!

The same hardware should be used but connect from the vertical Stack to

the horizontal Pipe so all can move together.

Took a bit of arguing to persuade him.

This is not an uncommon situation.

I have a rather pricey Maule Muffler that only lasted 25 hrs since new

for a similar reason.

“ It’s almost new ; do we still have to etc etc “ could be a temptation here.

It wasn’t.

If the moving parts contact fixed components you WILL have a failure.

Aircraft such as Mooneys use a ball/socket arrangement to allow flexing

in the system.

Overtightening the joint hardware would again restrict needed flexing.

These same types have a hanger on the firewall.

Too tight= no flex.

Missing /broken results in a load on the Pressure Can & failure.

The worst I’ve seen sent tonight!!
 
If you have a Power Flow, the ICA require you to remove, disassemble and pressure test the exhaust components at annual. I had a leak in my exhaust, and did that operation. It's no big deal, especially if you do it every year. That hardware get tough to remove after a while.
 
RyanB said:
How did it cause his death?
Click to expand...
The tailpipe extension added weight and inertia and the pipe tore out of the muffler. A fire started in the engine compartment. CO was also a likely factor. Cessna 185.
 
I agree with Dan 100%.

Too common.
 
I’m not a fan of calling the feds when defects are found.

This one was close though.

There are not a lot of folks that are alive because of an engine failure.

At least two pilots are.

Wintertime and a172 splits a cylinder (AD) right over an airport.

Cowl removal revealed an even bigger but insidious concern.

On Lycoming 172s there is a Bumper Pad fastened to the Alternator attachment.

The Pad contacts the Lower Cowl to accept the loads pushing the Cowl back.

IF it was installed .

This aircraft was missing the component.

This allowed the Cowl to be forced back into the Airbox and Muffler.

This action wore several holes in the Pressure Can which would contaminate

the heated air.

IMHO flying in winter over the Appalachians could have been disastrous

if the Cylinder had not failed.

This aircraft was a rental and what really #*);&-# me off was finding the

possibly life saving fresh air vents were taped over on the Wing Inlet.
 
So the bottom line seems more to be that its just a bad idea to heat your cabin with the exhaust system.

I've seen a few of the cabin heat valves, on light GA almost none of them close fully or seal off 100% The inner 'cylinder' always seem to stay open .25in or so.

But the FAA seems to be worried more about internal defects and cracks more than CO2.

I don't think I've ever seen a small GA shop with a dunk tank big enough to submerge a exhaust system to look for bubbles
 
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