So an interesting, if sobering update to this tale. I know my door seals have exceeded their useful life, so before I replace them anyway I decided to take a little flight on Monday and replicate the cabin configuration from my Idaho flight a few months back - i.e. wing vents closed, cabin vent and heat on just a little bit. Defroster is a constant source of air as it's stuck half-open. My meter placed near the copilot's chart pocket read nearly 90ppm before long. I then moved it on top of the center tunnel between the trim and fuel selector, and it hit 140ppm! I didn't leave the plane like this any longer, and immediately vented everything. Within about 30 seconds I was back down to <10ppm. While 140 sounds high, it would still take a few hours of exposure at this level to start to affect anything, so for purposes of this flight all was fine.

Things that amazed me a bit with this experiment:
1. How much small positional changes affect CO levels, at least with momentary bursts like this.
2. How much I must have actually been breathing in with this cabin config set for as long as it was. I now have no doubt, I was experiencing minor CO poisoning (probably compounded by decreased O2 at my altitude), which explains the headache and slight nausea and cognitive issues. I've read that the headache feels different, very focused in the forehead, and it was in this case. That actually turns out to be a pretty good diagnostic tool. Don't ignore the physical sensation, or that gut instinct that says something isn't right!
3. How quickly it changes. I went from a 10ppm baseline to almost 90ppm within seconds of closing off the cabin. This also means that if a leak develops in flight, conditions can change extremely quickly.

Also worth noting: I contacted the sensor manufacturer and confirmed a suspicion, that the sensor is only accurate at the elevation (air pressure, really) that it was calibrated at. Unless the sensor adjusts for altitude on its own, it will always read low as you climb higher than the calibration elevation. This follows standard atmospheric pressure math, so at my altitude of 7200ft on Monday, I was actually pulling in about 170ppm at times. While I don't know the altimeter setting at time of calibration, I do know it was done at sea level. If I assume 29.92, I can also adjust the "true" value by 0.33% for every inHg of deviation. Very few (if any) portable sensors will do the altitude adjustment, and it bears checking on your panel-mount kit as well if you have one.

Knowing what I do now, I feel pretty lucky that all I experienced previously was a headache, sick stomach, and some delayed mental ability. The plane is going in Thursday for some other work anyway, so it isn't leaving the shop or flying again until it's sealed up tight.

No matter which one tickles your gizzard, buy a real CO sensor, not a little brown dot. The hype turns out to be valid.

denalipilot wrote:I don't recall ever seeing one of those press-on CO stickers that has turned black. How black do they get? How dark would indicate a dangerous situation?
-DP

... HOWEVER
(1) ya gotta LOOK AT IT TO KNOW THERE'S A PROBLEM.
(2) they don't work at night, in low light, or when deep shadows in the cockpit wash out color.

colopilot wrote:

... I've read that the headache feels different, very focused in the forehead, and it was in this case. That actually turns out to be a pretty good diagnostic tool. Don't ignore the physical sensation, or that gut instinct that says something isn't right!

... if a leak develops in flight, conditions can change extremely quickly.

Also worth noting: I contacted the sensor manufacturer and confirmed a suspicion, that the sensor is only accurate at the elevation (air pressure, really) that it was calibrated at. Unless the sensor adjusts for altitude on its own, it will always read low as you climb higher than the calibration elevation. This follows standard atmospheric pressure math, so at my altitude of 7200ft on Monday, I was actually pulling in about 170ppm at times. While I don't know the altimeter setting at time of calibration, I do know it was done at sea level. If I assume 29.92, I can also adjust the "true" value by 0.33% for every inHg of deviation. Very few (if any) portable sensors will do the altitude adjustment, and it bears checking on your panel-mount kit as well if you have one.

This is a very interesting post. I hadn't thought about the affect of altitude on CO partial pressures. I guess if the engine is burning about the same amount of fuel, at about the same efficiecy level the amont of CO created through combustion could be constant, and the net result would be an increasing proportion of CO in the cockpit gases. Evil!

Just curious: does everyone have their exhaust system disssembeled and leak checked at every annual (or at least once a year if doing progressive/100 hr inspections)?

PapernScissors wrote:

colopilot wrote:

... I've read that the headache feels different, very focused in the forehead, and it was in this case. That actually turns out to be a pretty good diagnostic tool. Don't ignore the physical sensation, or that gut instinct that says something isn't right!

... if a leak develops in flight, conditions can change extremely quickly.

Also worth noting: I contacted the sensor manufacturer and confirmed a suspicion, that the sensor is only accurate at the elevation (air pressure, really) that it was calibrated at. Unless the sensor adjusts for altitude on its own, it will always read low as you climb higher than the calibration elevation. This follows standard atmospheric pressure math, so at my altitude of 7200ft on Monday, I was actually pulling in about 170ppm at times. While I don't know the altimeter setting at time of calibration, I do know it was done at sea level. If I assume 29.92, I can also adjust the "true" value by 0.33% for every inHg of deviation. Very few (if any) portable sensors will do the altitude adjustment, and it bears checking on your panel-mount kit as well if you have one.

This is a very interesting post. I hadn't thought about the affect of altitude on CO partial pressures. I guess if the engine is burning about the same amount of fuel, at about the same efficiecy level the amont of CO created through combustion could be constant, and the net result would be an increasing proportion of CO in the cockpit gases. Evil!

Just curious: does everyone have their exhaust system disssembeled and leak checked at every annual (or at least once a year if doing progressive/100 hr inspections)?

We do all of our customers planes. It's and AD that had to be complied with on any aircraft with a heat muff in Canada. Is it an AD for you guys in the US as well?

Sent from my SM-G870W using Tapatalk

A1Skinner wrote:
We do all of our customers planes. It's and AD that had to be complied with on any aircraft with a heat muff in Canada. Is it an AD for you guys in the US as well?

Sent from my SM-G870W using Tapatalk

In my case (C172 with powerflow, O-360) it's ICAW. I've not seen an AD. I'll ask next time I see my very fine IA.

Last year when my IA called to tell me that a flange had broken off my exhaust system and that he recommended that the whole thing be replaced rather than just welding the flange back on, he also told me that by tapping the pipes, he could tell that there were some weak spots. I had no hesitancy to have him order the new exhaust--CO is simply too dangerous to mess with.

I have noticed that my Pocket CO will show a reading if I have to idle very long with the window open, such as in a conga line at OSH. It depends some on wind direction. It's never been enough to set off the alarm, though.

I think the source of the CO needs to be found in any airplane--just sealing it isn't good enough, because if there's a leak caused by a leaky exhaust, that also means very hot gasses are escaping, which could lead to fire at worst and under cowl damage at best. However, sealing is a good idea for other reasons.

In addition to sealing doors and windows, replacing the steering rod boots on my airplane with Kevlar versions sealed off the draft that was coming in there--obviously not an issue with a taildragger, but worth considering for any nosewheel airplane. I don't think I was getting any exhaust through them, but I was getting cold air in the winter.

My door seals are good--they had been replaced just before I bought the airplane 14+ years ago, and they're still good. But I have replaced the seal in the opening window and the baggage compartment. Both came from Aircraft Door Seals LLC, https://www.aircraftdoorseals.com/. If I have to replace the door seals, I'll buy from them. Their instructions are easy to follow, although admittedly the seals are a pain in the wazoo to install for us klutz mechanical types--I'm sure my IA could have done my window and baggage door much more quickly than I did.

All of this sealing has made my airplane much warmer in the winter.

Cary