Hey all

Flying with a fancy CO meter that will read the parts per million of carbon monoxide, what’s the normal level in a safe plane?

Zero I’m not buying as practical, but I’ve read some folks who go a little crazy on the high side too, so what is a normal healthy non pressurized piston old school bush plane reading in the cockpit?

I've used a number of CO monitors like that over the years. The only time I had one read higher than zero in cruise flight was when I left the fuel sump drain door open on the Bonanza. Doh! It's about a foot behind the exhaust and pretty much wide open to the cabin after that. Otherwise, occasionally 5-10 ppm on the ground and maybe 2-3 in climb but that's about it. Also, running LOP keeps CO levels low even if there is a bit of exhaust gas finding its way into the cabin.

That applies to the Bonanza, the Husky, a PA-28-236 and the Grumman AA1-B we used to have.

All that said, I just put a cargo pod on the Husky and have been told to expect 2-3 ppm CO in cruise. Haven't seen that yet, but obviously some folks have.

Belloypilot wrote:I've used a number of CO monitors like that over the years. The only time I had one read higher than zero in cruise flight was when I left the fuel sump drain door open on the Bonanza. Doh! It's about a foot behind the exhaust and pretty much wide open to the cabin after that. Otherwise, occasionally 5-10 ppm on the ground and maybe 2-3 in climb but that's about it. Also, running LOP keeps CO levels low even if there is a bit of exhaust gas finding its way into the cabin.

That applies to the Bonanza, the Husky, a PA-28-236 and the Grumman AA1-B we used to have.

All that said, I just put a cargo pod on the Husky and have been told to expect 2-3 ppm CO in cruise. Haven't seen that yet, but obviously some folks have.

I Agree with the above. I have a super sensitive CO detector. I keep it in my flight bag. Helpful if I am training students in other planes for picking up CO poisoning. If the windows are open on the ground I typically will see somewhere between 2-10 ppm. As soon as I close the windows and start flying it goes to zero.

https://portal.ct.gov/-/media/departmen ... 725F4383FF

Attached is a chart showing the real danger levels of CO poisoning. 70 ppm seems to be the level at which symptoms can occur. Of note - when I had my avionics installed. The shop installed a belly vent cover in the wrong direction. This vent improves the ventilation in the airplane by opening the bottom fuselage with a vent. The vents are supposed to be pointed outward toward the aft section of the airplane and to the right so that the air doesn't come into the airplane. After the install I started getting headaches, lightheaded, nauseated, and fatigued after short flights. Bought the CO detector. First bought a cheap ASA colorimetric card. The cards are worthless. I even put the card on the exhaust of a friends airplane and it didn't change color. I am guessing the colorimetric cards go black right about the time you are actually dead. Anyway - bought a sensitive CO detector. Actually too sensitive reads from 1-50 ppm. It was immediately reading > 50 ppm.

Thought I had an exhaust leak at first and then inspected the whole plane and noticed the vent being installed in the wrong direction and fixed the problem. Good to know what a little bit of CO poisoning feels like and also good to keep a good CO detector handy. There are better units for aviation. I wouldn't worry about low level readings on the ground. I think this is normal. Windows open and propeller slipstream from the exhaust is the cause.


Josh

I checked OSHA's website for CO exposure on the job when I got mine. OSHA considers 50 ppm acceptable for an 8-hour workday, 40 ppm is acceptable for a 10-hour shift.

Seems this plane is making about 10-15ppm I’ll take a closer look but everything looks right minus the window and door seals which are pretty loose, that number is also with the Cessna wing root vents open

Two winters ago I went down a rabbit hole with CO in my 170. The "worthless" little CO pucks were turning dark while I had the heat on. I bought a real CO detector (Sensorcon AV8). When I pulled heat I was getting north of 100PPM. On my 52 170 the mixing valve for the heat pulls air from the engine compartment, in my case the exhaust was not coming in around the muff but instead from the mix air within the cowl.

After replacing half of my exhaust and cleaning/tightening fittings I was still getting 20+PPM in flight. Sealed all the panels in my belly and got down to 0 PPM in flight with the heat on and everything closed.

I'm seeing 2-10 PPM on the ground and in a prolonged climb. 0-5 PPM in flight with or without heat. 0PPM with the vents open.

I attached a photo of a new vs exposed CO card (The photo was taken about an hour after I landed).

I had one of the Sporty"s version for a couple of years and the only time it turned dark was flying over KJFK at 5000" one day.

I haven't posted on here in a while however this topic is near to me, as a CO event almost killed me about 6 years ago over Wyoming. Since then I've spent many, many hours researching the topic, and have even put together a ~45 minute presentation to help educate other pilots. I'm not going to drop all that here, but want to share some bits of relevant information.

First, CO poisoning is about rate of exposure. A short, high level exposure can be as bad as a long term low level exposure. It is also cumulative, meaning that it dissipates from blood far, far more slowly than it accumulates. So that 100ppm event over several hours becomes a life threat even though the value itself isn't going to harm you for a short period of time.

With respect to meters or sensors, the color changing cards are less than worthless as I think they give a false sense of safety. They have a short lifespan measured in months which is decreased with exposure to sun (like in an aircraft cockpit), are affected by moisture, and don't reset. After my personal event I bought a SensorCon portable detector, which is great because you get a display with measurements. I still have that in the plane, but have since added a Guardian CO sensor tied to my CGR-30 display which gives me PPM readout and bright, blinky alarm lights if it detects anything.

Now, also realize that most sensors are not pressure adjusting! If they are they will likely advertise that feature (some Guardian versions are, for example). They are designed to measure parts per million against a calibrated air sample, which is basically wherever the factory is and usually somewhere closer to sea level. As you climb in altitude they begin to read low, roughly in proportion to the reduction in atmospheric pressure. So my expensive SensorCon and non-adjusting Guardian panel sensor read LOWER than actual PPM values in a non pressurized cabin like my 182. At 12,000 feet this means that a readout of 150ppm is really more like 219ppm exposure.

Combined with hypoxia and CO's incredibly strong bond compared to O2 (210 times stronger!) attaching to the hemoglobin in your blood, altitude + CO is a really bad combination. What is an annoyance at ground level can amplify in flight, especially flying high over terrain on cross country trips like many of us here do.

200ppm can cause headache, nausea, and dizziness as well as cognitive impairment similar to hypoxia in just a few hours. Now go up in altitude where you have less O2 to oppose CO anyway and you can see where this becomes a real issue. 400ppm is considered life threatening after 3 hours. Note that these ppm values are for sea level exposure as well.

I tested my aircraft after the fact and my exposure was somewhere around 250ppm (calibrated for the low reading) at 12-12.5k altitude. I was over Wyoming in winter with the vents mostly closed, and a steering boot crack was all it took. I breathed that in for 5-6 hours over the course of a day feeling progressively worse, and was about one bad decision away from a lethal outcome. That story is a longer one, but after understanding CO vs blood volume I estimate I was maybe an hour away from loss of consciousness, but what I was about to do due to cognitive decline wouldn't have taken that long.

Buy a real detector, something that can be calibrated and has a PPM readout. It doesn't need to track baro pressure as long as you understand it will read low as you climb in proportion to atmospheric pressure decrease. Pay attention to it. A single or low digit (10-20ppm) exposure isn't a "stop flying" thing, but you should open a vent and get it looked at soon. Into mid double digits I'd start taking more steps - lots of fresh air, killing heat, finding a repair shop asap before continuing the trip. Any more than that and I'm landing the plane knowing what I know now.

Take this stuff seriously. It will sneak up on you and kill you.

Aviation Consumer has published several articles on CO in the past several years. Their last big CO detector review was in March 2022 and they recommend the detectors made by CO Experts and Aithre. I bought a CO detector based on their advice and use it periodically, especially when I use cabin heat. I should use it more.

I forget what their annual subscription costs but it isn't much in the grander scheme of things. It is the only print magazine I still get and I read it every month.

CO detectors are budget dust for airplane owners. If you can afford an airplane you can afford a CO detector.