CO leak

[65eTurbo]

Hi all.  I need a little help diagnosing a carbon monoxide leak. I'm showing about 15 PPM While taxiing but as much as 50 PPM in flight. I've blocked off the heater duct at.the firewall so I know it's not coming from a heater leak.  If I open the cabin vent pull on the panel, and put the sensor in the airstream it quickly drops to zero so it's not coming in through the vent system. I found an open gap in the floor panel ahead of the spar and have taped that over with aluminum tape. I also removed the screen on the air exit on top of the fuselage over the baggage compartment with no noticeable difference.  The levels don't seem to vary with the gear up or down. We've buttoned the firewall up tight with RTV on the smallest pin holes. We've also aluminum taped over the hole at the back of the nose wheel well which enters the belly pan area.  The problem seems to have cropped up after the installation of the new interior so I'm likely faced with determining whether there is now inlet leak that's open or I've blocked off the number of exit leaks that kept the levels low.  Thoughts anyone?

[carusoam]

Use the CO monitor and move it around the cabin while in flight…

See where the numbers get higher…

They can be coming from odd places like the cable tray at the back of the cabin…

Any new antenna wires get installed?

 

PP thoughts only…

-a-

[Hank]

Don't forget the openings in the floor at the rudder pedals. How tightly does the door seal?

[Davidv]

Door seal - that’s often the culprit.  Any imperfection creates a vacuum and sucks in exhaust from around the fuselage.  Do a paper test in flight where you move a sheet of paper around the door seal area to see if any part sticks.

[Yetti]

Have you pulled all the old duct tape on the floor and resealed with alum tape?  Takes about a day.   There are lots of holes around the wheel well.

 

[EricJ]

2 hours ago, Yetti said:

Have you pulled all the old duct tape on the floor and resealed with alum tape?  Takes about a day.   There are lots of holes around the wheel well.

 

In mine there are holes in the floor from the footwell all the way back through the baggage compartment.    The potential sources for CO entry are numerous.

 

[Yetti]

3 hours ago, EricJ said:

In mine there are holes in the floor from the footwell all the way back through the baggage compartment.    The potential sources for CO entry are numerous.

 

Yes.   Wing roots and all sorts of holes.   Just thinking the holes next of the exhaust would be more primary suspects.  redo the whole plane

 

[Skates97]

You can also check and see if there is a duct that comes off the top of the right inlet scoop to the back of the avionics stack. My plane had one to cool the avionics in days gone past and I would pick up CO readings from it depending on the phase of flight. With the newer avionics it is no longer needed so I capped it off and haven't seen the readings since then.

[exM20K]

Have you checked your detector? I just sent my 6 year old Tocsin unit in for sensor replacement.  Sensor is good for two-ish years.  Maybe another pilot near you has something you could borrow to check your device.

-dan

[Marauder]

Have you pulled all the old duct tape on the floor and resealed with alum tape?  Takes about a day.   There are lots of holes around the wheel well.
 

Amen brother. My CO meter would always show a low background level. I had already pulled and replaced the duct tape under the rear seat with high quality waterproof 3M aluminum tape.

When I did my rugs, I found a bunch of seams and little holes that were covered with duct tape as well. I spent that day sealing all of those as well.

I now see CO values at 0 in cruise.




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[Marauder]

And BTW, who’s idea was it to use glue to hold down the rug??!!


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[Ragsf15e]

Mine isn’t sealed very well, however I show 0ppm in cruise from my sensorcon.  10-15 is normal on the ground.  Depending on the wind on the ground and my parking in relation to the wind, I have seen 50+.  Turning 90 degrees fixed that, so I know I’ve got leaks.  Here’s my point though… in cruise, the leaks might make a little difference, but they are unlikely to make a huge difference if your exhaust is properly mounted/pointed and all the exhaust connections are solid.  I think I’d look carefully at the exhaust from each cylinder and follow all the way to the pipe.  Make sure it’s pointed exactly as others.  Airflow can do some weird things.

[Yetti]

and the standard remove the scat tube on the muffler shroud and look for signs of leaks.  borescope is your friend here.

[Ragsf15e]

I had an exhaust issue that manifested on the co monitor.  I saw increases both in the air and on the ground, which is why this one is a little weird.  Mine was a completely disconnected exhaust pipe at the cylinder connection… pretty much 3 hours after annual.

Edited July 23, 2021 by Ragsf15e

[Marauder]

and the standard remove the scat tube on the muffler shroud and look for signs of leaks.  borescope is your friend here.

You ain’t living unless you do a nice deep exhaust borescope exam.




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[ShuRugal]

Mine isn’t sealed very well, however I show 0ppm in cruise from my sensorcon.  10-15 is normal on the ground.  Depending on the wind on the ground and my parking in relation to the wind, I have seen 50+.  Turning 90 degrees fixed that, so I know I’ve got leaks.  Here’s my point though… in cruise, the leaks might make a little difference, but they are unlikely to make a huge difference if your exhaust is properly mounted/pointed and all the exhaust connections are solid.  I think I’d look carefully at the exhaust from each cylinder and follow all the way to the pipe.  Make sure it’s pointed exactly as others.  Airflow can do some weird things.

Adding to this... You WANT fresh air to be leaking into the cabin, unless you've somehow got a pressurized Mooney. Need air to breath.

Any unpressurized aircraft is going to see intermittent exhaust ingress on the ground depending on wind angle. If air can get on for you to breath, exhaust can be blown in by the wind.

The important thing is that you get no ingress in flight, any phase, and that when on the ground you can clear the ingress by turning into the wind.



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[Ragsf15e]

2 minutes ago, ShuRugal said:

Adding to this... You WANT fresh air to be leaking into the cabin, unless you've somehow got a pressurized Mooney. Need air to breath.

Any unpressurized aircraft is going to see intermittent exhaust ingress on the ground depending on wind angle. If air can get on for you to breath, exhaust can be blown in by the wind.

The important thing is that you get no ingress in flight, any phase, and that when on the ground you can clear the ingress by turning into the wind.



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I guess it’s nice to have most of that air ingress through locations that minimize the chances of exhaust ingress.  Like air through the side vents is fine, but through the gear wells and floor would be less desirable.  I definitely agree though, she’s not sealed air tight!  

Just for comparison, pressurized airplanes aren’t sealed either.  They all leak - usually around the door.  In fact, there are built in vents to control the leaking.  There’s enough cooled, pressurized bleed air being pumped in to attain the appropriate pressure with excess that is then leaked out to keep the pressure.  I descended through smoke in a PA46T, and I can smell it.

[65eTurbo]

It looks like we finally nailed down the CO issue.  A lot of the aluminum tape inside the cabin had been removed during the new interior install.  The worst leaks were an untaped area in the copilot wing root area that was open to the belly but full of tubes and such and the entire panel separating the tailcone from the cabin.  In particular, holes with wiring and tubing passing through on the pilots sidewall into the tailcone.  Thanks for all the help everyone.

[carusoam]

Great follow-up 65e!

Thanks for sharing the details.

Best regards,

-a-

[65eTurbo]

Hi all.

A further follow up on my CO issue.  I continued to have issues in flight, but low level.  No issue on takeoff, but leveling off in the pattern increased CO and gear down made it worse.  I was also seeing some CO in cruise, but only toward the back of the plane.

I finally found one more culprit.  The Johnson bar boot was a loose fit on the bar, allowing a quarter inch gap which generated quite a breeze of 30-40ppm (sensor in the flow) air.  A zip tie installed very loosely while on the ground then slipped down mid-swing and tightened while gear-up in flight resolved that leak and seemed to knock it down to near zero.  Now I need another long debugging flight to see just how much residual CO I can find.

Another thing I discovered in reading a response technique for CO in the cockpit, and then validated in flight is... go lean of peak!  Lean of peak, CO is zero. So, ever get CO in the cockpit in a single (won't work with a fuel heater on a twin)?  Go lean of peak. I couldn't detect any CO anywhere while lean of peak, even before fixing the Johnson bar boot.  Just one more reason why lean of peak rocks!

Also, I kept scaring myself, wondering how much was too much to test fly. I kept freaking out when seeing 15 ppm on my sensor for a minute.  Turns out, residential sensors only show a non-zero value above 29.   I finally found these guides, which I found credible and indispensible:

https://www.handlebar-online.com/writing-tips/what-is-a-dangerous-level-of-carbon-monoxide-ppm/

https://www.carbonmonoxidekills.com/are-you-at-risk/carbon-monoxide-levels/

0-0.5 = level of CO in clean fresh outdoor air, such as far out at sea or in remote wilderness.
0.1-1 = level of increases in average outdoor CO–within current outdoor ranges of 0-5 ppm– that are associated in over 100 epidemiological studies with significantly increased risks of mortality and morbidity from many cardiovascular and respiratory disorders and, in growing fetuses, with low birth weight and birth defects–even after adjusting for the effects of other pollutants (ozone, SO2, NO2 and particulates) in multi-pollutant analyses.

0-2  = CO level in exhaled breath of healthy non-smokers who do not live with gas ovens, but only if not recently CO poisoned, not acutely stressed, and for women, not in the premenstrual phase of their cycle.

0-3 = range of max 8-hour avg. ambient CO in most US cities.  This range has declined significantly since 1970s when above 9ppm as use of catalytic converters in vehicle exhaust became more common. See EPA graph of ambient CO data.

0-29 = CO range in which consumer CO alarms are allowed to continuously display ZERO but not allowed to display the actual CO level, according to CO alarm standards developed by Underwriters Laboratories (UL2034) in collaboration with the US Consumer Product Safety Commission.  (The display and alarm specifications of UL2034 are matched in a Canadian standard, CSA 6.19-01)

3-15 = CO level in breath of non-smokers with flu, PMS/PMDD, chronic diseases, chronic low-level CO exposure (such as living with gas ovens) or recent more acute CO exposure.

7 mg/m3 = maximum (max) 24-hour avg exposure established by WHO for Europe in 2010.  Although ostensibly meant to allow less total exposure than other WHO CO standards (see below), this standard actually allows more than twice as much total CO exposure as WHO’s max avg 8-hour exposure standard.
9 = max 8-hour avg outdoor ambient CO level allowed by US EPA, unchanged since first adopted in 1971.

9   = max indoor CO level recommended by the American Society of Heating, Refrigeration and Air Conditioning Engineers in a voluntary building industry standard (ASHRAE 62.2).

10 mg/m3   = max 8-hour avg CO level allowed by WHO and the European Commission.

10-30  = CO level in exhaled breath of smokers within one to two hours after they last smoked. Exhaled CO in smokers remains chronically above 5ppm until days after they quit smoking.

25   = max 8-hour avg CO level allowed in occupational settings for an 8-hour workday over a 40-hour workweek by the American Conference of Governmental Industrial Hygienists.

25   = CO level above which Baltimore fire department requires firefighters to put on self-contained breathing apparatus.

30 mg/m3   = max 1-hour avg CO level allowed by WHO.

30 = CO level at and above which consumer CO alarms are allowed (but not required) by
UL2034 to continuously display the actual CO level.
30-50   = lowest CO range in which consumer CO alarms are required by European Norm standards (EN50291) to sound, but only after this level  has been continuously sustained for 2 hours.
30-70 +/-3   = lowest CO range in consumer CO alarms are required by UL2034 to sound, but only after this level  has been continuously sustained  for over 30 days.  This is meant to (and effectively does) insure that consumer CO alarms never provide any warning at CO levels below 70ppm.

30-999+   = CO level exhaled by smokers while smoking and by non-smokers during acute high level CO poisoning.  In any high level CO environment, your exhaled breath CO level will gradually rise but remain lower than the ambient level because you always absorb some of the CO you inhale as long as the level in air is higher than the level in your blood.  As soon as you stop smoking or move to a lower CO environment, you start exhaling.

[PT20J]

10 minutes ago, 65eTurbo said:

Another thing I discovered in reading a response technique for CO in the cockpit, and then validated in flight is... go lean of peak!  Lean of peak, CO is zero. So, ever get CO in the cockpit in a single (won't work with a fuel heater on a twin)?  Go lean of peak.

Perfect combustion of a hydrocarbon yields CO₂ and H₂O. CO is an intermediate product produced by incomplete combustion when there is more fuel than air to complete the conversion. This is why a lot see increased CO during climb (rich mixture) and less when they lean to peak or LOP in cruise.

Skip

[65eTurbo]

7 minutes ago, PT20J said:

Perfect combustion of a hydrocarbon yields CO₂ and H₂O. CO is an intermediate product produced by incomplete combustion when there is more fuel than air to complete the conversion. This is why a lot see increased CO during climb (rich mixture) and less when they lean to peak or LOP in cruise.

Skip

Yep.  Some old fuel injection systems used %CO measured in the exhaust by the mechanic as a means of setting mixture as CO rises predictably as the mixture richens.  My Porsche was set to 1% CO for example.

It had never occurred to me, however, to be sure to be lean of peak if the CO monitor alarmed as it would resolve any CO issue on a single.  Obvious after the fact.

[carusoam]

Combustion efficiency defined and explained!

Great details.

 

Our engines can be CO factories….

CO is best dumped out the end of the tail pipe…

 

Too often, a leak between pipe connections, or a hole in the muffler, allows CO out too early…

The worst is when a hole in the muffler dumps CO into the cabin’s heat system…

 

-a-

[jaylw314]

4 hours ago, 65eTurbo said:

25   = max 8-hour avg CO level allowed in occupational settings for an 8-hour workday over a 40-hour workweek by the American Conference of Governmental Industrial Hygienists.

Industrial Hygienists??  Who came up with that name??