Carbon Monoxide

Recently, using a sensitive Carbon Monoxide detector, I discovered that using the heater in my SR22 resulted in unacceptable levels of CO in the cabin. This is certainly NOT unique to Cirrus aircraft.

I’m posting here as a reminder to all that CO is a serious and potentially deadly problem for the General Aviation fleet. Some references follow…

Air Safety Foundation Says Carbon Monoxide Accidents Rare But Deadly

Carbon Monoxide Detectors for Aircraft Use

Getting Ready for Winter Operations

CO Experts Model 2002

Learning My Lessons

Marty SR22 N464M


Exactly what levels are you getting in your SR22?


SR22 N258ST #307

Found the link to an FAA STC’d panel mount CO detector (I think). The link is

Unfortunately, it is one of those sites that stresses style over function and my browser balks at some of the java code. Haven’t gotten to the item of interest yet.

Shouldn’t be so hard. Must have been written by a windows devote.



I occasionally get readings of 10-15ppm during slow flight, and got steady 20ppm one time when I left the baggage door open. But I don’t get readings from the heater, so you should definitely get your system checked.

I trained in Katana’s, and they produce ~10-15ppm readings much of the time (DA20-A1’s) since the air intakes are rather close to the exhausts. Once I saw that I never took one above 5000’.

Carrying a sensitive CO detector can be enlightening. I had it go off in a taxi in Bellingham WA. I asked the taxi driver if he got headaches, and he said all the time. I told him he might want to keep the windows open until he had the car checked.

At San Carlos which is located next to Highway 101, when there is a gentle breeze blowing from the freeway direction at rush-hour I get readings of 10-12ppm on the ramp!



In reply to:

Exactly what levels are you getting in your SR22?

In cruise, heater off 0 ppm, heater on 17 ppm and climbing. Seeing that number I shut off the heat and the reading returned to 0 ppm. (For the detector I was using, 0 ppm only means something less than 10 ppm.)

Back on the ground I used the recent max value function on the detector and saw 25 ppm. Note that home CO detectors alarm at something like 70 ppm that has endured for over several hours. But, I like to be conservative and also recognize that being at altitude makes CO even more dangerous (since we already have less O2 available).


What kind of CO detector are you using?

Marty, I’ve also got a CO detector in my 22 and have not yet seen anything show up in flight. If I taxi with the door open and have the detector near the door it alarms almost instantly.
I’ll check and see at what threshold (PPM) the indicator starts to register. It may be 10 ppm like yours (I got mine at Aeromidix as well but it’s a different manufacturer).
Aviation Consumer recently had an article on CO detectors that you should be able to access from their web site if you’re a subscriber. It’s a valuable reference on how much CO is too much.

Thank You Marty.

I am glad you have brought it to our attention. I think this winter we all should install a monitoring unit. Good brain function is important for a good flight!



Senco Sensors Model ONE Low-Level CO Monitor (follow the link in the first sentence :slight_smile:


I followed the link in the first sentence of your note and then followed the link on where to buy it to Airmedix. However at that site a different unit is offered for sale. It sounds good but it is not the Senco unit mentioned on the first link. Where did you get yours?


I got my Senco model one from aeromedix, but they no longer carry that item.

There was a recent hint of a CO detector being developed for STC’d panel mount in aircraft. I’ll try to find that info and will post.


I have a neat installation of a CO guardian model 352. I have a picture of it but I don’t know how to reduce it so it will fit on the COPA site. I will be happy to send it to anyone.
Oh, hey, it is a big file but I think it is small enough. OK here it is.


I followed the links with no problem. The CO Guardian LOOKS like a very nice box. I’ve seen an installation in a Cirrus that I think was the Aero 252, and it looked pretty cool.

However, on reading the .PDFs of the manuals, I notice that for any CO level less than 40 ppm, they indicate “Normal”, and they don’t beep until the level reaches 50 ppm . Mike Busch of AVweb writes that anything above 35 ppm is an emergency.


  • Mike.


In reply to:

I don’t get readings from the heater, so you should definitely get your system checked.

Already at the Service Center. Thanks,


In reply to:

I have a neat installation of a CO guardian model 352. I have a picture of it but I don’t know how to reduce it so it will fit on the COPA site.

Here is Myron’s photo, reduced and brightened a bit.

Myron: How complicated was the installation and what was the cost?

What was the total, for the unit and installation? Was there any trouble getting the form 337 approved?

Aviation Consumer rated earlier models of the CO Guardian well. This is apparently a more recent model.

Myron: I have been considering installing one of the CO Guardian detectors in my Diamond Star. I wasn’t aware that the 352 had an STC. Supposedly CO Guardian is working on a new model (452) that will receive FAA approval. I’m ignorant of what kind of documentation is required to install non-STC’d equipment in a production aircraft. Right now I’m using a Senco Model 1. For reference, in my airplane, the highest in-flight reading I’ve ever gotten is zero; highest on the ground with the canopy cracked is 20 ppm.

I liked the way you had it build in.
can you provide me some more info like a web-site .
what kind of cost can I expect?


We will have our two Cirri delivered in early April, and after discussing the CO issue, we would like to follow your way of layout, since it looks very professional.
Can you help me in obtaining the following info:

  • Who is the MFG of the CO Guardian ( web site ?)
  • Price indication ?
  • do you have a template for the build in or other suggestions.

Lot of thanks

Jaap Zondag
CirruShare BV

I had the installation done last winter. If I remember correctly, it took about two hours. There is very little room to spare near the throttle quardrent so one needs to be careful there. The mechanic made a template so the cutout ended up flush for a nice look. The unit comes with extra wire so a remote light can be mounted. I thought I would need it but the warning sound is loud enough to hear at cruise and with Bose headsets on. There is enough room in the circut breaker panel for the extra breaker needed.
I showed this to Mike R at ACK this summer.