I am considering the purchase of an SR-22, and have a question about CO. Recently I bought an AIM-935 as recommended on AVWeb to monitor CO levels in the Diamond Katana’s I’m training in. I’ve been surprised to see levels from 7-30ppm in various stages of flight in planes across the line. I’m wondering if anyone has carried a low-level CO monitor in their Cirrus to see what the levels are.
In the Katana, the exhaust is not far from the cabin air intakes and certain flight attitudes seem to be worse than others.
For comparison, when I start my car in my garage with the door open and back out, levels in the car rise to the 10-12ppm range. Idleing on a freeway in rush hour traffic can also rise to the 7-12ppm area. Most home CO detectors do not sound until at least 35ppm. The AVWeb article on CO is at:
I’m not real happy with the CO detector (I have the same one - AIM 935).
The first one I bought, on the way back from Duluth, went from “Lo” to 35 ppm, then back to “Lo”, then hovered around 10-11 for a while, then back over 20, etc. within the span of about 30 minutes, with no changes in ventilation, mixture, throttle, altitude, etc. When it went above 30, I was just about to decend and make a precautionary landing at the nearest airport to have it checked out (while still in Minnesota at least) when it started decreasing again.
I returned that one (the folks at Aeromedix were very accomodating) and got a replacement, thinking that there was just something wrong with that one.
The one I have now is a little more consistent, but quite often does go above the threshold for beeping (I think it’s 9 ppm, but I don’t remember). I often see readings in the mid teens, although just as often I see readings of “Lo”. Can’t seem to correlate it to any particular throttle setting, ventilation setting, attitude, etc. Just seems random.
Like you, I’ve often seen these “teen” readings in other planes, too. So I have to accept this as “normal”. Plus I don’t think that even a few hours exposure to mid-teen level CO will do any harm.
The problem is that because it starts beeping at such a (relatively) low level, it’s sort of like the boy who cried wolf – I’m so used to it beeping that I just ignore it, and am considering not even carrying it anymore since it’s so annoying.
Given what I’ve seen in planes so far, I think I’d prefer having one that only beeps above say 20-25 ppm - at least then I’d KNOW I have a problem and can start making plans to get down right away.
I don’t think this helps answer your question very much but it did allow me to vent!