Observations with a carbon monoxide detector

I got a carbon monoxide detector after hearing Max Trescott’s podcast on the subject. I shared it with my students too and almost all of us bought one. I’ve been using it for nearly six months now and I wanted to share and compare with others experiences.

1. I never see zero. Well, if I turn it on outside, but it is never zero in a running plane. I’ve gotten it down to low single digits but not zero. The highest readings come from idling on the ground when not moving.

2. I can tell when I have leaned or not. Leaning does some to lower the value. Whether airborne or on the ground.

3. Retiming my mags lowered the value. The values were getting too high on the ground. I had the exhaust inspected the same time I had the mag retimed and the timing advance turned on my Surefly mag. It lowered my values to an average inline with the other airplanes I fly.

4. I see about 12-24 ppm while on the ground and taxiing. It will drop to 1-10 ppm while in cruise flight and leaned. When my mag was out of time, I would see up to 60ppm while idling on the ground.

What do you guys see?


1963 Cherokee 180 B.


  • Hi Paul,
    I just had a Guardian Aero 455 combination CO detector / pulse oximeter installed in my Arrow and connected to my JPI EDM-830 engine monitor for display and scanning. They are finishing it and I should be able to fly with it this week sometime. I'll let you know what I see. ... I agree on having one and Guardian makes excellent products. I'm mounted mine in the lower left hand corner with a Century autopilot would normally go. I had a Guardian USB power port installed at the same time and location so I could run a short wire to my Ipad.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Piper Owner Society Forum Moderator and Pipers Author.

    Need help? Let me know!

  • Hi Paul, you say you do see zero when outside the aircraft? Inside the aircraft, on the ground with all avionics ON but no engine start, do you see zero? Wondering if it is being affected by electric fields in the aircraft. Does it truly go up only on startup? Does it change when you transmit?

    If it really is indicating only CO gasses, that must be a very sensitive unit. Also, does the sensor have a lifespan and require replacement?


  • It is a gas detector. Electrics have no effect at all.

    It is supposed to be recalibrated every couple years.

    I keep the unit on the panel where the glove box should be.


    1963 Cherokee 180 B.

  • Yes, the unit is designed to detect CO gas, but it is not uncommon for supporting electronics to be sensitive to noise on the power input (unless battery powered), induced pick up by close proximity to other equipment due to poor shielding, or being swamped by the strong fields created by an improperly terminated transmitting coax. I once had a graphic engine monitor that would go nuts every time I hit the push to talk!


  • I see. I don’t think it has that problem. It works the same before and after my avionics master goes on or off.


    1963 Cherokee 180 B.

  • I do see zero in flight and sometimes on the ground while taxiing but it’s usually in the low single digits. When I forget to lean, it will pop up to above 50 ppm and start its way down after I lean or after I taxi and get some air circulation. I try to pay close attention in the colder months after I turn on the heat in case of a leak into to heating system. I fly a 1978 Warrior.

  • Do you have a link to the device you are using? I would love to get something installed in my plane...

  • I am using one of the portable devices from amazon that Max suggested. It appears to work well. 79 PA-32-300 in cruise I have zero. Taxi I can get from 3-15 or a pretty good spike depending on if the copilot door is open for ventilation and which way the wind is blowing relative. I trust it, and the beeping alarm and flashing LED are enough to get your attention when needed.
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