[Piper J3]

I flew this morning to two outlying airports. Beautiful day… 75F. I flew solo with min fuel so airplane was light and responsive. I did full-stall landing on hard surface runways at each airport and discovered Carbon Monoxide detector registered ~10ppm after rollout. Taxi, takeoff, and cruise are 0 ppm. The CO detector registered on each of the two landings.

Here is what I think is happening…. I landed full-stall, very nose-high, and greased the main wheels on. I held the nose up until speed decayed and front wheel lowered to the ground. The nose-high attitude rolling on the ground compresses the air under the airplane and causes air flow (exhaust) on right side of airplane to raise up and enter the open cabin vent.
-

 

[PilotjohnS]

Co working?

I always wonder if my CO is working or not because it always reads zero.

Then one day, I was sitting behind a cessna 172 from a local flight school, and lo and behold, I got a reading of 6. So old Cessnas are not only slow, but they put out……..

But now I know my CO is working

 

[jneves]

I see the same thing on slower nose high landings. It drops back to zero very quickly. Great way to test the monitor for function. I have the same unit and it's great. Added one to the motorhome as well to be extra safe.

 

[coffeeguy]

I sometimes see 8-10 ppm on my Cherokee when I'm on takeoff climb and the vents are open. As soon as I drop the nose it goes to 0. Looks like the same CO detector.

 

[RicoB]

Mine also reads anywhere from 3-9 on runups at times and 5-7 on take off.It clears out after few min. I need to borrow a different one and use both at the sometime to compare and see what I get.

 

[Desert Rat]

That's the problem with instrumentation having gotten so precise. We used to be blissfully ignorant of stuff like that.

I've flown a couple of planes now that have had the CO detector show something either during taxi with a specific wind component, or on climb out.

note- strange how the mind works; as I was typing this, I had a random memory of driving a tractor when I was a kid. That thing had a straight pipe that stuck up just a couple of feet in front of the driver and smelled like exhaust all the time.

 

[Marlonyoung]

CO

I have noticed in high Alpha slow flight and stall practice the reading goes up, but acceptable range

 

[storm_pilot]

I have the same unit in my Super Cub and it will read about 10-15 ppm during mixture rich + high AOA operations (takeoff and landing). Leaning helps a lot as does increased speed.

FWIW, I was a hazmat tech in a previous life and I wouldn't worry too much about readings below 50 ppm. The OSHA time weighted exposure limit is 50 ppm/hour, for 8 hours.

I like that you have a replacement date placarded on the unit because the sensors do go bad over time. They typically start reading high when they do.

 

[Ethanol1]

I have the same unit in my Super Cub and it will read about 10-15 ppm during mixture rich + high AOA operations (takeoff and landing). Leaning helps a lot as does increased speed.

FWIW, I was a hazmat tech in a previous life and I wouldn't worry too much about readings below 50 ppm. The OSHA time weighted exposure limit is 50 ppm/hour, for 8 hours.

I like that you have a replacement date placarded on the unit because the sensors do go bad over time. They typically start reading high when they do.

I think this is bad advice. CO has a cumulative affect in your blood. See this video link.

https://www.youtube.com/watch?v=ONNtA4mCi8Y

 

[storm_pilot]

I think this is bad advice. CO has a cumulative affect in your blood. See this video link.

https://www.youtube.com/watch?v=ONNtA4mCi8Y

Yup. CO has a cumulative effect. Thats why OSHA set the "safe" threshold at 50 PPM. Your body can expel it as fast as it is absorbed for an 8 hour period at 50 PPM.

https://www.osha.gov/sites/default/files/publications/carbonmonoxide-factsheet.pdf

I wasn't looking to start an argument. Zero PPM is also safe but often quite difficult to attain and usually well outside of the margin of error for the affordable sensors that we carry around with us.

Personally I use that monitor as a trend device. If I were to suddenly be getting readings in the 20s or 30s then I would investigate further as to what changed.

 

[rcarsey]

I have the optional Aithre module installed in my 12iS. Its installed in behind the PFD; and the two fans keep a fresh supply of cabin air flowing to it..

Without wing root seals, I would frequently see up to 4 PPM during climbs.. but once the seals were installed, I can't say I've ever seen anything other than 0 PPM. The module itself does a self-test on power-up; which verifies that the wires from it to the G3X are still connected OK (you'll see 255 PPM for about 10 seconds, then it goes back down to 0).. but I guess that doesn't mean the CO sensor itself is actually doing its CO detecting thing.

I did notice a constant 1-2 PPM at one point and at the next oil change I noticed an exhaust spring had broke..

 

[Brantel]

I have the optional Aithre module installed in my 12iS. Its installed in behind the PFD; and the two fans keep a fresh supply of cabin air flowing to it..

Without wing root seals, I would frequently see up to 4 PPM during climbs.. but once the seals were installed, I can't say I've ever seen anything other than 0 PPM. The module itself does a self-test on power-up; which verifies that the wires from it to the G3X are still connected OK (you'll see 255 PPM for about 10 seconds, then it goes back down to 0).. but I guess that doesn't mean the CO sensor itself is actually doing its CO detecting thing.

I did notice a constant 1-2 PPM at one point and at the next oil change I noticed an exhaust spring had broke..

Can you tell me which model Aithre you have?

 

[subpar_bucker]

I don't want to put words in Rob's mouth, but I'm pretty sure he used the one called out in this service letter:

https://www.vansaircraft.com/wp-content/uploads/2020/05/SL-00010.pdf

 

[rcarsey]

Yes.. I followed SL-00010 and ordered the optional kit (the RETRO kit in my case, since my wiring harness was pre-2020) through Van's.

The EX 3.0 is a CO detector, oxygen bottle pressure sensor, and SPO2 sensor -- it requires power, and 3 analog inputs into the Garmin GEA24 (engine monitoring box on the firewall). The EX 2.0 is CO Detector-only.. but with Van's pricing.. for $400, you get the 3.0 unit, and all the connectors/pins/wire you need to connect it to your post-2020 wiring harness.. so you're not saving much $ by trying to buy the EX 2.0 elsewhere.

I initially had hooked up all 3 lines to the GEA24 (thats what the plans call for), but later on, I had wanted to hook up a Smart Glide button .. and I needed the extra inputs...so I ended up disconnecting the additional wires and essentially only have the CO detector part of it wired in.

Because you'll have the latest wiring harness, it'll just a matter of drilling 4 holes to mount the unit after you receive your 12IS CO DETECTOR KIT

 

[seagull]

At what ppm level should we be concerned?

 

[Brantel]

Yes.. I followed SL-00010 and ordered the optional kit (the RETRO kit in my case, since my wiring harness was pre-2020) through Van's.

The EX 3.0 is a CO detector, oxygen bottle pressure sensor, and SPO2 sensor -- it requires power, and 3 analog inputs into the Garmin GEA24 (engine monitoring box on the firewall). The EX 2.0 is CO Detector-only.. but with Van's pricing.. for $400, you get the 3.0 unit, and all the connectors/pins/wire you need to connect it to your post-2020 wiring harness.. so you're not saving much $ by trying to buy the EX 2.0 elsewhere.

I initially had hooked up all 3 lines to the GEA24 (thats what the plans call for), but later on, I had wanted to hook up a Smart Glide button .. and I needed the extra inputs...so I ended up disconnecting the additional wires and essentially only have the CO detector part of it wired in.

Because you'll have the latest wiring harness, it'll just a matter of drilling 4 holes to mount the unit after you receive your 12IS CO DETECTOR KIT

Thanks!

Not that I need it yet and don't want to buy until I do since the sensor has a limited life, I looked at the Van's webstore and the kit is backordered.

I also noticed that Van's charges a $95 premium for three pieces of small wire less than a foot long for the folks needing the retrofit kit.... If that is not a mistake, holy cow batman! Looks like that kit is in stock....wonder why?

Also thanks for the note on the inputs. I will likely never use the SP02 and Tank pressure features so won't plan on consuming inputs with unnecessary connections. I will probably just stick with the EX 2.0 since I have all the stuff that Van's includes with the install kit and save myself a $100 bill or whatever the difference is when I get around to purchasing.

 

[Dvalcik]

At what ppm level should we be concerned?

I have heard under 20 to 30 ppm is ok. I have added a chart from a quick search on co levels. I occasionally see 2 ppm, but nothing high. This graph is from my light speed zulu3 app.

 

[seagull]

I'm just thinking out loud here, dont blast me.

Many GA aircraft get cabin heat from a cuff around the exhaust. A leak in the exhause can allow CO through the heat tube into the cabin, a big issue.

The -12 gets cabin heat from the coolant radiator so no exhaust is involved since it is all ducted separately. The -12 cabin is "leaky" through the landing gear and other openings so there is always a flow of air. If built properly there is no place for air to pass through the firewall. I am wondering if it is even possible to get a high enough concentration to be a problem.

 

[Webb]

Keep in mind that barometric CO monitors adjust for altitude and are used in aircraft. Portable handheld units are calibrated at sea level and any present CO is reported as the concentration you would find at sea level.

Partial pressure of CO decreases ~ 3% per thousand feet. So….. at FL100, if it reads 50 PPM, it would be the same as a concentration of 65 PPM at sea level.

Handheld units that do not compensate for altitude and exposure is greater than what is measured which is a concern.

 

[thiggins]

I'm just thinking out loud here, dont blast me.

Many GA aircraft get cabin heat from a cuff around the exhaust. A leak in the exhause can allow CO through the heat tube into the cabin, a big issue.

The -12 gets cabin heat from the coolant radiator so no exhaust is involved since it is all ducted separately. The -12 cabin is "leaky" through the landing gear and other openings so there is always a flow of air. If built properly there is no place for air to pass through the firewall. I am wondering if it is even possible to get a high enough concentration to be a problem.

Vans changed to a heat muff around the muffler for the iS. I suppose the water type did not provide enough warmth, and/or it did not warm quickly enough. I was surprised to find that in my iS build.

 

[R100RS]

For a number of reasons, I believe that the OSHA PEL (permissible exposure limit) of 50ppm is NOT appropriate for aviation use.

First, OSHA is not assuming that the exposure will occur thousands of feet AGL where the partial pressure of oxygen is lower than at ground level and the adverse effects of CO may consequently be exacerbated.

Second, the private pilot population is not young and likely (despite passing a Class III FAA physical) includes many pilots with undiagnosed disease of the lungs, heart, and cerebral circulation. So, there will be some pilots (and passengers) for whom modestly elevated blood CO levels (actually, elevated carboxyhemoglobin levels - ie, the percent of hemoglobin molecules that are rendered unable to transport oxygen because they are tightly bound to CO) may produce undesirable impairment.

Third, OSHA PEL values tend to be obsolete. For example, the WHO Guidelines for Indoor Air Quality - Selected Pollutants (2010) recommended a 1 hour CO exposure limit of 31ppm and an 8 hour exposure limit of 9ppm. I believe these guidelines are more appropriate for prevention of adverse effects among humans. California OSHA (CAL/OSHA) has an 8 hour CO exposure limit of 25ppm.

FWIW, I am board certified in internal medicine and board certified in occupational medicine. I have been familiar with the medical literature on CO for decades and I have evaluated many workers who have been exposed to low levels of CO. In my own airplane, if my CO detector shows a level of 10ppm - 20ppm, I would open all vents that introduce outside air and I would want to find a place to land in the next 30-60 minutes if the levels were not below 10ppm after doing so.

NOTE: Nothing I have written here should be considered medical advice or medical care. Entire books have been written on this topic and I have written only a couple hundred words. Consequently, my comments are not a complete discussion of the issue. DO NOT TAKE MY COMMENTS TO IMPLY A SPECIFIC ACCEPTABLE LEVEL OF CO FOR YOU AS PIC OR FOR YOUR PASSENGERS.

 

[Panzer]

Ok, so... went to sun n fun and was fortunate enough to win a Delta Zulu in a giveaway. Yeah! I took the Aithre monitor I had literally just picked up from Spruce back for a refund. Imagine my surprise when the CO alert alarm goes off an hour and a half into my flight home. Over 50ppm. Well, what do you do? Seriously, clear day, no heat on, cabin vents open - what is different? Turn the cabin heat on - any change - did it go up? Nope, same. Figure if it was a leak into the cuff and I OPEN the heat duct, I should see an increase. So where is it coming from? Then like five minutes later it drops down, and finally just goes away. Then about a half hour later it pops back up again. Five or ten minutes and it drops away again. Scratching my head. I've had the plane up twice since and seen nothing, then today on the way home from a quick 30 minute flight it jumps all the way to 90! At 5500 and I had a quartering tailwind at the time and have to figure that the quartering wind is sending exhaust back into my fuselage somehow. Pulse ox showed 93. Climbed to 7500 which but the wind directly off the tail and the reading dropped to 3, pulse ox back up to 95. I know pulseox doesn't read CO, but still thought it was interesting data in the moment.

What troubleshooting, seals, mods, parts, adjustments, etc... let me get after this and figure out what is wrong?

 

[newt]

At 5500 and I had a quartering tailwind at the time and have to figure that the quartering wind is sending exhaust back into my fuselage somehow.

How would that happen?

- mark

 

[Mich48041]

The airplane (while flying) does NOT know which way the wind is blowing.
The wind can not possibly affect anything on or in the airplane, except make it bumpy.
The only thing wind can do is affect ground speed.
Try another CO detector to see if it gives the same warnings.

 

[Plummit]

The airplane (while flying) does NOT know which way the wind is blowing.
The wind can not possibly affect anything on or in the airplane, except make it bumpy.
The only thing wind can do is affect ground speed.

Two words: Wind Shear.

-Marc

 

[rv8ch]

What troubleshooting, seals, mods, parts, adjustments, etc... let me get after this and figure out what is wrong?

Two things to look at. 1) you are probably running too rich, which causes less efficient burning of fuel, and thus more CO. If you lean more, then you will generate less CO. 2) exhaust fumes are getting into the cockpit, somehow. Many people have reported that exhaust fumes can get in from the tail of the aircraft or the flap pushrods, and that opening air vents increases the pressure in the cockpit, reducing the influx of exhaust from the tail. From what you described that opening the vents didn't change anything, I would recommend checking for cracks in the exhaust system (something that should be done yearly anyway).

Getting a second CO detector sounds like a great idea. Any CO reading when in flight is very bad, and should be fixed immediately.

 

[Panzer]

I know, the quartering wind comment seems highly unlikely - but I have literally nothing else changing in flight conditions, and the CO starts up, peaks, then drops back down... seemingly in concert with direction of wind shifting. Could be coincidence and my imagination as well. Swimming in a river of air, I get it. I asked a friend with a Masters in Aerospace Engineering if he thought I was nuts, and he said probably, but schmaybe not. We'll see. Didn't mention, but running LOP the whole time, so no, the problem isn't mixture. Plus I don't want it lower, I want it zero. I have now completely watched all of the fascinating vid of the guy who passed out and survived the subsequent 'auto-land' event in his Mooney, plus the equally interesting Martin Pauly interview with the expert med guy. I know I want zero CO, or as close to it as I can get within the error tolerance of the detector. Current plan - ordered wing push-rod boots, pulling the cowling tomorrow for a thorough exhaust, heating system, firewall inspection, and if still stumped, will work to seal rear cabin bulkhead. Only other thing I haven't messed with is that the builder installed a custom 'cowl flap' for additional oil cooling (before going to a better oil cooler) and I didn't think to check that in flight. Might be it was open, as it has near-zero impact on performance (or oil cooling) and it isn't in the checklist, nor in the regular row of switches, so I likely overlooked it. Possible it is a contributor based on position, but I think that's pretty unlikely, as its fully forward of the firewall, and should be an air egress not intake. Still, I should have thought to open/close it to see if it changed anything. Regardless, will continue to TS and post results.

 

[Dugaru]

I asked a friend with a Masters in Aerospace Engineering if he thought I was nuts, and he said probably, but schmaybe not.

Could you ask him to explain how the direction of the wind could even schmaybe make a difference? I totally don’t get it. I could maybe see how bouncing around in turbulence might erratically change the flow of CO in and around the airplane, but the direction of the prevailing wind seems totally irrelevant. But I am ready to sit corrected!

 

[bjdecker]

Saw this is another RV-12. Run a piece of aluminum tape along the cowling/fuselage seams - vertical sections and the small horizontal section which is in line with the air vents. Fly again and report back.

 

[Paul 5r4]

I have a friend here with an RV 14. He had exactly the same issue. Only with very high AOA's he'd get warnings. I suggested he close up the little holes on the tail aft of the fuse. That small flat area back there. He did with some RTV. Problem solved.

 

[Panzer]

@bjdecker and @Paul 5r4 could you guys show pix of where particularly you mean?

 

[Jamesey]

Something wrong with your new headphones?

 

[Paul 5r4]

Panzer, Sorry, I don't have any pictures. I'm talking about the area all the way aft on the fuselage.... the end of it. It's just forward of the rudder. The fuse area where the bottom rudder hinge bracket is mounted and your taillight wire comes out. That area there. My RV 14 friend sealed those up and the CO alarms stopped.
Ok, found a picture. Click on the photo and see the arrow. I'm talking about the aft end of the fuse between the fuse and forward of the rudder. Hope this helps.

 

[bjdecker]

@Panzer see attached picture - yellow circle.

 

[Panzer]

Thanks guys - so either CO seeping out of the engine box and into the air vents through the side piano hinges, or through the tail assembly. I will investigate both, although the readings didn't change with opening / closing the vents, so I'm inclined to discount that one a little. A&P buddy and I are going to check the exhaust assy in full tomorrow, and I will see about the tail. I had thought of trying to seal directly behind the baggage compartment, as easier to get at, but will look over the tail assy carefully. If a tube of RTV or equivalent will do it, I'll be quite happy. If exhaust inspection, and tail sealing don't work, I'll tape the inside of the cowl, especially directly forward of the NACA ducts and see if that alleviates it. Thanks for the help!

 

[Panzer]

Something wrong with your new headphones?

Never know. The LiON Battery it came with was defective - wouldn't take a charge - and I had to get them to ship me a new one. Would love to baseline with a different detector, but don't have one readily at hand (yet!).

 

[Foghorn]

I’m wondering how we survived all those years without electronic CO detectors. My RV and 195 have elevated levels when taxiing with a tailwind. Never had an issues in flight. Been using electronic for a few years now.

 

[Panzer]

So, determined the following today. The exhaust system leaks, but not inside the heat cuff. We put pressure into the exhaust and got significant leakage at every join - downstream from the ball joints, as well as at the straight join just below the headers, on both sides. The exhaust system is a Vetterman.

Leakage at top (right) of pipe clamp, just prior to ball joint. Ball joint does not leak itself.


Leakage at join on crossover pipe, right side of hose clamp visible on left side of photo. Also leaks at top of pipe clamp in center of photo. What looks like a crack in the middle of the top of the 'Y' on both the top pipe clamp and the pipe itself, is just a bad angle on the photo. No crack actually there.

Is some degree of leakage into the cowled area forward of the firewall just assumed to occur? A 'normal' condition? If I assume that the answer is yes, I am back to modifying the cabin's overall in/out flow profile. Firewall looked good - no obvious leaks. Also no easy way to put pressure on it to find any.

Pulled the tail access panels and will get in there with some RTV soon. Looking in/around the tailwheel spring mount pass through, primarily. Any/all holes on the bottom. Any other areas to look at let me know. I think I can also potentially seal a bit around the rudder cable pass-through conduits.

Will also install aileron push rod seals when they arrive, as well as working to seal off the upstream seams in the cowling to fuselage join (piano hinge and Skybolts) to prevent engine compartment gases seeping into NACAs, per recommendation. No easy way to do this inside the cowling, so may test fly a couple times before I resort to an external tape test, if a problem remains after the above efforts.

Lastly, I may also install weather strip along the back of the aft canopy skirt to see if that limits inflow. If none of this works, will advise and ask for more input. Only thing I can think of at that point is to throw out the Vetterman and buy an new exhaust. Consulted my builder and he indicated he was never pleased with the 1.5" exhaust system - thinks he got sold on a system that promised more than it delivered and wished he had gone with 1.75" pipes. Also, the crossovers seem more complex than necessary - why not just straight out? Recommends on folks to talk to about the exhaust system? I figured I would call Powerflow and let them try to sell me, just to learn at least.

Oh, and I got my first oil change done, with help from my A&P. Fifty flight hours since purchase, going strong and still grinning!

 

[ravenstar]

Ok, so... went to sun n fun and was fortunate enough to win a Delta Zulu in a giveaway. Yeah! I took the Aithre monitor I had literally just picked up from Spruce back for a refund. Imagine my surprise when the CO alert alarm goes off an hour and a half into my flight home. Over 50ppm. Well, what do you do? Seriously, clear day, no heat on, cabin vents open - what is different? Turn the cabin heat on - any change - did it go up? Nope, same. Figure if it was a leak into the cuff and I OPEN the heat duct, I should see an increase. So where is it coming from? Then like five minutes later it drops down, and finally just goes away. Then about a half hour later it pops back up again. Five or ten minutes and it drops away again. Scratching my head. I've had the plane up twice since and seen nothing, then today on the way home from a quick 30 minute flight it jumps all the way to 90! At 5500 and I had a quartering tailwind at the time and have to figure that the quartering wind is sending exhaust back into my fuselage somehow. Pulse ox showed 93. Climbed to 7500 which but the wind directly off the tail and the reading dropped to 3, pulse ox back up to 95. I know pulseox doesn't read CO, but still thought it was interesting data in the moment.

A pulse oximeter measures hemoglobin saturation, but doesn't differentiate what it is saturated with. Normally hemoglobin carries oxygen, but carbon monoxide binds far more aggressively and displaces oxygen. That's why it's so dangerous. A person suffering from CO poisoning may well show a pulse ox reading of 100%, but that doesn't mean they're getting enough oxygen to their tissues. Don't assume a high pulse ox reading means you're ok if your CO monitor says you've got elevated levels. (I spent 25 years as an EMT, and this was a favorite question on the EMS certification exams.)

 

[rv8ch]

Lots of RVs flying happily with no CO leaks with the Vetterman exhaust. Some leakage at those exhaust system joints will be normal, but eventually they will leak less as exhaust deposits "seal" them. This CO will flow out the bottom of the cowl and be mixed with the actual exhaust which has a lot of CO. Not sure if you mentioned it, but are all your firewall penetrations sealed? That's very important for both CO and fire protection.

If the FW is totally sealed, then you are looking at something finding a way back into the cabin via one of the openings between the FW and the tail, as others have mentioned. Sounds like getting another RV expert pair of eyes on your aircraft would be a good idea.