A little excitement on one of the flights today

[Al Downs]

Student and instructor flying today. They had flown earlier and came down after noticing an exhaust smell and seeing the CO indicator turning colors. They said it was only when using cabin heat. We called our mechanic and made arrangements to go to them to check it out. They were available in about 2 hours so the instructor and student said they would go up again and not use cabin heat. Everything was fine, no smell so they continued. They did a few landings and then on final while at idle the engine ran away going up to 3900 rpm and running very rough and shaking. They had the airport made so they shut the engine down and deadsticked it in. No body hurt and no damage.

 

We removed the top cowl and found the throttle cable on the left side broken allowing that carb to go full throttle. There is nothing within at least one inch of the cable in this area and certainly nothing sharp to cause this damage. I really don't understand why it broke. I was able to use a piece of wire to secure throttle linkage in the idle position so we could idle it back to the hangar.

 

There is a picture attached.

 

Anyone have an idea what would cause this?

[ralarcon]

Student and instructor flying today. They had flown earlier and came down after noticing an exhaust smell and seeing the CO indicator turning colors. They said it was only when using cabin heat. We called our mechanic and made arrangements to go to them to check it out. They were available in about 2 hours so the instructor and student said they would go up again and not use cabin heat. Everything was fine, no smell so they continued. They did a few landings and then on final while at idle the engine ran away going up to 3900 rpm and running very rough and shaking. They had the airport made so they shut the engine down and deadsticked it in. No body hurt and no damage.

 

We removed the top cowl and found the throttle cable on the left side broken allowing that carb to go full throttle. There is nothing within at least one inch of the cable in this area and certainly nothing sharp to cause this damage. I really don't understand why it broke. I was able to use a piece of wire to secure throttle linkage in the idle position so we could idle it back to the hangar.

 

There is a picture attached.

 

Anyone have an idea what would cause this?

Thanks for the PIREP, have never seen or heard of that happening , but I will surely check my throttle cables.

Thanks ! Glad everything turned out Ok !

 

Cheers

[Roger Lee]

Mutant termites.

[Anticept]

That looks like a place where the cable frayed at the edge of the bowden cable sleeve for part throttle settings. Make sure there are no burrs.

 

As a side note (not related to this, but something that people should be looking for): if the cable is adjusted a lot, the pinching action wears on them where you cinch down with the retaining screw and sleeve. In addition, the retaining screw and sleeve should freely spin in the arm, and if they don't, it causes work hardening. Apply bearing grease and try to make sure the cable and screw move freely so it is not bending the cable.

 

I'm still looking into it, but I've thought about using a shrink tube around the area that the retaining screw cinches down on to help decrease wear and serve to relieve some of the stress. However, I've had second thoughts about it because it makes inspection a lot more difficult.

[IrishAl]

Did you find the source of the carbon monoxide?

[Al Downs]

No not yet. Will be looking at that today and will post results.

[Jim Meade]

I was not there and it's both easy and dangerous to pontificate from afar, but I think if I were the instructor in this case, I would not have taken the airplane up again without at least a close visual inspection, using lights and mirrors and other tools as appropriate, focusing on the exhaust system, and including the cabin heat connection.

 

I'm not sniping and looking for an excuse to find fault. Here are my reasons for making this statement.

 

As a CFI, this is a teaching opportunity. The student would be shown that a reasonable person would at least inspect the engine before flying again. The CFI would reinforce that CO is insidious and doesn't necessarily depend on exhaust gas smells to indicate it's presence.

 

Each of us can be expected to decowl an airplane to look at it for any reason at all. It doesn't take long and it isn't difficult. The Student gets the idea that perhaps especially when it's easy to make an inspection, it is reasonable to do so.

 

I can't think of how I'd explain to the FAA or anyone's parents/spouse if something happened that was so easy to check out for obvious defects.

 

It was not said if another CO detector was taken up on the second flight. It would seem to be a good idea if the flight was made at all.

 

I'm as human as the next person, perhaps more so. I operate farm machinery that is probably not as safe as it could be sometimes. The purpose of this post is only to suggest there may be opportunities to make a teaching point that the student would undoubtedly take to heart and learn from.

 

I, too, would like to learn what was determined as to the cause of the CO. Yes, I do, at least partially due to the encouragement of a pilot friend, have a good, current CO detector in my CTSW. I don't have one in the Champ and I guess I should. I think I will skip on in my glider.

 

Edit: I've been thinking about this a little and have to say it is my opinion that the airplane was unairworthy and should not have been flown the second time.

[Tom Baker]

For the cable, I wonder if someone has clamped the cable with something during maintenance for some reason and damaged the cable.

[herrdrpepper]

Greetings,

I am a student LS pilot and have enjoyed and benefitted from lurking on this forum .

I think what Jim Meade said about the airworthiness of the plane after there was ANY concern about carbon monoxide is really important.  The notion that CO is detectable in exhaust odors has resulted in death.  CO is totally odorless.  Detectors in the cockpit make great sense.

Also his point regarding the student’s education in dealing with these issues is valuable.

Thanks for a great forum,

Tom

[FastEddieB]

My guidance would be:

 

Any time the word "probably" sneaks into one's thought process, a little warning should go off in one's head.

 

"That tire looks a little low, but it'll probably be fine for this flight"

 

"I would have thought I'd have more fuel left at this point, but I probably have enough to make it all the way."

 

"I don't feel 100% this morning, but I'll probably be fine."

 

"My destination currently has a much lower ceiling than forecast, but it will probably improve."

 

"That's a pretty strong and gusty crosswind, but I can probably handle it."

 

And finally...

 

"I think I smelled exhaust, but we'll probably be OK for one flight."

 

Saying a successful outcome is probable, is to admit that a less successful one is at least possible. And this ties into "Most Conservative Action".

 

We're all familiar with wishful thinking. But that kind of thinking is often the first link in a chain that can lead pilots to tragic results.

 

Just sayin'!

[Mick]

RiGHT ON 

[FastEddieB]

And no one's perfect...

 

Scenario: day after Christmas with my family and Tiger in Hartford, CT. Plane used to FL heat and it was freakin' COLD up north.

 

Preflighting to head home, noticed a small puddle of brake fluid under the right brake. Thought, "Not used to the cold - it will probably be fine and I'll troubleshoot when we get home."

 

And guess what - it was fine for the trip home.

 

But...

 

After starting up, the engine felt noticeably rougher than normal while taxiing. I thought, "Not used to the cold - it will probably smooth out eventually".

 

And it did. Runup and departure went fine and we were level at 6,000' over Long Island Sound.

 

Then all h•ll broke loose and the engine started shaking hard and backfiring. No combination of mags and mixture and carb heat and throttle made any difference. Declared an emergency and with partial power headed to the nearest airport on Long Island. Trucks were waiting as I circled down to a successful landing.

 

Exited the plane with the family and immediately saw oil all over the nosewheel fairing. Sinking feeling as I wondered if I had left the oil cap off. But opening the cowling, the problem became all too obvious:

 

 

A frozen exhaust valve gives the pushrod nowhere to go and the exhaust gasses nowhere to go except back out the intake. Not good. And the oil was escaping from the end of the hammered pushrod tube*.

 

Anyway, "morning sickness" is a common symptom that precedes a frozen valve in a Lycoming O-360. The engine tried to warn me, but I wouldn't listen.

 

Live and learn!

 

 

*I still have the bent pushrod and tube, kept as a reminder of my fallibility.

[Anticept]

YIKES glad it didn't start a fire, the exhaust gasses could have caused a backfire (NOT an afterfire, learn the difference ).

[FastEddieB]

I actually considered using the correct term, but thought it too pedantic...

 

...even for me!

[Anticept]

I actually considered using the correct term, but thought it too pedantic...

 

...even for me!

 

Just be sure to be clear with your mechanic if you ever bring it up, or they will spend time looking in the wrong place!

[Doug G.]

I would add to this conversation that the little button CO detectors are not particularly sensitive. By the time you get an indication there is a lot of CO in the cabin.

[FastEddieB]

Just be sure to be clear with your mechanic if you ever bring it up, or they will spend time looking in the wrong place!

Wait.

 

It's not like I can't easily slip into pedantic mode...

 

It was a long time ago, but I remember "popping" sounds.

 

Visualizing the Otto Cycle:

 

 

If the exhaust valve was stuck closed, the exhaust gas would have to wait until the intake valve opened to escape out of it into the intake manifold.

 

So, it would likely not have been traditional afterfiring (mixture burning in the exhaust/muffler) or backfiring (mixture burning in the intake manifold/carb) unless that unexpected pressure in the manifold really screwed up something somewhere.

 

As an aside, the repair was done without removing the cylinder - the valve was pushed into the cylinder, the guide reamed, and then the valve was fished back out with fishing line and patience. And then new pushrod, tube and seals, of course.

[Anticept]

If the exhaust valve was stuck closed, the exhaust gas would have to wait until the intake valve opened to escape out of it into the intake manifold.

 

So, it would likely not have been traditional afterfiring (mixture burning in the exhaust/muffler) or backfiring (mixture burning in the intake manifold/carb) unless that unexpected pressure in the manifold really screwed up something somewhere.

 

As an aside, the repair was done without removing the cylinder - the valve was pushed into the cylinder, the guide reamed, and then the valve was fished back out with fishing line and patience. And then new pushrod, tube and seals, of course.

 

Exhaust gasses are way above the autoignition point, and probably did start a fire in the intake manifold if they escaped through the intake (backfire), however it would have been sucked right back into the engine as the piston lowered. Subsequent leaks back into the intake wouldn't be as bad, because the constant action of the spent charge being pushed out and pulled back in would exclude fresh fuel and air, and I imagine that cylinder would start to act like a low compression cylinder at that point.

 

As a side note, If you ever have a carb fire, the solution is to close the fuel valve and keep cranking to suck the fire into the engine.

[WmInce]

Scenario: day after Christmas with my family and Tiger in Hartford, CT. Plane used to FL heat and it was freakin' COLD up north.

 

Preflighting to head home, noticed a small puddle of brake fluid under the right brake. Thought, "Not used to the cold - it will probably be fine and I'll troubleshoot when we get home."

 

And guess what - it was fine for the trip home.

 

But...

 

After starting up, the engine felt noticeably rougher than normal while taxiing. I thought, "Not used to the cold - it will probably smooth out eventually".

 

And it did. Runup and departure went fine and we were level at 6,000' over Long Island Sound.

 

Then all h•ll broke loose and the engine started shaking hard and backfiring. No combination of mags and mixture and carb heat and throttle made any difference. Declared an emergency and with partial power headed to the nearest airport on Long Island. Trucks were waiting as I circled down to a successful landing.

 

Exited the plane with the family and immediately saw oil all over the nosewheel fairing. Sinking feeling as I wondered if I had left the oil cap off. But opening the cowling, the problem became all too obvious:

 

A frozen exhaust valve gives the pushrod nowhere to go and the exhaust gasses nowhere to go except back out the intake. Not good. And the oil was escaping from the end of the hammered pushrod tube*.

 

Anyway, "morning sickness" is a common symptom that precedes a frozen valve in a Lycoming O-360. The engine tried to warn me, but I wouldn't listen.

 

Live and learn!

 

 

*I still have the bent pushrod and tube, kept as a reminder of my fallibility.

Great story and lesson for all of us Eddie.

Concur with your thoughts regarding "complacency," totally.

Thanks for sharing.

[Doug G.]

There is a Mike Busch article in the latest EAA Sport Pilot which says the chemical button CO detectors are basically worthless. It is worth a read.

[FlyingMonkey]

There is a Mike Busch article in the latest EAA Sport Pilot which says the chemical button CO detectors are basically worthless. It is worth a read.

 

I always assumed these are more of a "feel good" solution than a really useful CO detector.  I have a friend in the EAA chapter with a very good (and pricey) digital CO monitor that I'm planning to borrow to get a baseline in my CT.

[Al Downs]

Update on the excitement we had a few days ago.

 

The latest round of repairs seems to have gone without a hitch. The initial repair was the broken throttle cable experienced by our instructor Matt and student Matt, forcing a dead stick landing. No idea how the cable broke but when this does happen, it goes full throttle. In this case we had one carb at idle and one at full throttle. Plane Safe Maintenance from Waukesha came to Racine to make the repairs. 

 

A small antifreeze leak was also fixed by replacing a small hose and hose clamps. We also addressed a smell of exhaust occasionally while using the cabin heat. We found a small hole starting to develop underneath the heater shroud. The muffler was sent to a FAA certified repair shop. Unfortunately every time they tried to weld the bad area, it would just get worse. New muffler needed ($1200 from Rotax). Unfortunately they couldn't get it to me until March. Flight Design had one in stock ($1900) it was a little different but they said it should work. 

 

A few calls around the country and one was found a Lockwood Aero in Florida. Still not simple as it was a kit with all the parts to make it identical. $130 to overnight it to Lawley Aviation in Burlington to assemble to make it match the bad one. Picked it up at 8:00 Tuesday morning and after a couple of hours of work it is as good as new. 

 

There is 1400 hours on the muffler when it went.  It might be worth  checking the availability of a muffler prior to needing it if you have a bunch of hours on yours. Unless you can wait 3 months.

 

One more more noticeable and maybe appreciable problem is the nagging problem we have been having is no heat. With the muffler out it was time to see if the heat could be fixed. Ever since an earlier repair 3 years ago we did not have heat. The problem was obvious now that it could be seen. The door for the heater was not opening and closing. At the last 100 hour inspection, we found the cable wrapped around a hose clamp and fixed that. It was warmer back then and it seemed to be fixed. Colder weather proved it was not quite right. 

 

Turns out that the cable was routed incorrect on an earlier repair and could not open and close the gate valve at all. No wonder it was so hot in the summer. Rerouted the cable and now the door opens and closes the way it should. I didn't fly it today because of the wind but I did taxi around and it was nice and warm. 

 

All the issues big and small have now been addressed and everything is in good shape. I will now tackle the weather and see if it can be fixed. 

 

 

 

 

[Marco01]

My muffler got a cracked of almost 10 cm long after 800 hours! I started to look for replacement, but a friend of mine said he can repair it since his working for Areva (Nuclear manufacturer) and using special soldering technics. They have done the job, and control it with X-ray: after now 200 additional hours of flight, no issues! i really thanks them for this excellent work done! I will post a picture of the repair later on... You now need to find somebody who could do the same, and got the right tools...

[Roger Lee]

Rotax exhaust are stainless and yes they do break occasionally. A lot of that depends on the original weld not being stress relieved correctly and or from being held under pressure from poor alignment while in use. This can be fixed by welding. Usually if a pipe cracks it does so all the way across. I have seen about a dozen over the many years and most just had them welded and have been fine ever since.

[FastEddieB]

Al said:

 

The initial repair was the broken throttle cable experienced by our instructor Matt and student Matt, forcing a dead stick landing. No idea how the cable broke but when this does happen, it goes full throttle. In this case we had one carb at idle and one at full throttle.

 

Good time to remind that if the engine gets rough at anything less than full power, going to full power at least has a chance of smoothing it back out.

 

Similarly if you've been cruising along at full power and it gets rough when you decrease power, go back to full power. Broken cable at full power would not be obvious until power was reduced.

 

In either case, a broken throttle cable should not necessitate an off-airport forced landing. Just cruise at full power to midfield downwind at the long runway of choice, kill the engine with the ignition and land.

 

Did the two Matt's do that?