[Genghis the Engineer]

I'd booked a beacon slot and planned 2ish hours of IFR practice in our PA28 shareoplane. We have an electronic carbon monoxide detector in the cockpit.

Pre-flight, I had a slightly higher than usual CO reading - around 11ish, not abnormally so as it often shows around 8, clearing quickly to zero after take-off, so I noted it, and proceeded with the flight.

Just after take-off the CO detector alarm went off showing 26ppm. I experimentally unclipped it and held it by the open DV window - dropped to zero. Put it back on the clip, went back up to 26, alarm went off again.

So, re-opened the DV window, and the side vents, called the field, did a circuit, landed, snagged the aircraft. Block time 18 minutes, airborne time 6 minutes.

Myself and another syndicate member opened and thoroughly went over the engine compartment - no cracks, loose joints, etc. visible anywhere. Spoke to the pilot who flew it last - he saw a slightly elevated 11ppm four days previously but hadn't been concerned.

So, aircraft grounded until maintenance can go over it. Some thoughts...


- It's an electronic device with a good clear audible alarm.

- 25-30ppm is reckoned okay for an hour (WHO guidelines). However I was planning 2hrs, mostly around 3000ft, likely in and out of cloud, so high workload, increased dependence upon my ability to function procedurally.

- Also, I got over covid a month ago and whilst back at work and flying, I'm aware of my lung capacity being significantly down (not that I'm physically incapable, but the week before I had covid I was running 30 miles a week, typically 5-7½ miles at a time, recovering afterwards in the time it took to drink a cup of tea - I'm presently struggling to achieve 12 miles a week, maximum 3 miles, and taking hours rather than minutes to get over it, so by *my* standards my fitness is somewhat degraded).

- A bit of googling suggests that people recovering from Covid arealso poorer at expelling CO, which suggest possibly to my uneducated mind an increased risk of CO poisoning?


We'll get to the bottom of this in January I think, lose a couple of weeks when we might otherwise have been doing a bit of pleasant flying.

But it's just possible that small loud electronic carbon monoxide detector just saved my life. As it is, we're mildly inconvenienced.

G

[Sir Morley Steven]

I flew our PS28 back from maintenance. It was winter and the heating was on max. Halfway back I checked the CO disc during a routine check and it was black. Heaters off, DV windows open and landed back with no problem apart from frozen extremities.
It was a crack in the exhaust inside the heater shroud. Couldn’t be seen unless the shroud was removed.

[johnm]

We have a small electronic detector too I used to have the discs but frankly rather lost faith in such things.

[Genghis the Engineer]

We have a small electronic detector too I used to have the discs but frankly rather lost faith in such things.

Likewise. There are very sound reasons for having an intrusive audio warning, as I think I demonstrated this week.

G

[riverrock83]

26ppm shouldn't be a health issue, generally you need to get nearer 200 ppm for a slight headache, fatigue, dizziness and nausea after 2-3 hours, although anything over 10 can be measured in the blood.
Glad all is well though, a change means a problem has occurred so hopefully they find it!

[GrahamB]

I have a small electronic detector on the panel. The alarm is uselessly inaudible but the flashing red lights draw attention.

SOP is for it to go off in a full power climb, reporting between 9 and 13 ppm. Once levelled off it settles back down to zero for the rest of the flight

One top tip - if you do have an alarm go off with a serious level being reported, lean the mixture as much as you dare. The closer you are to a stoichiometric mixture, the lower the proportion of CO produced.

[Genghis the Engineer]

26ppm shouldn't be a health issue, generally you need to get nearer 200 ppm for a slight headache, fatigue, dizziness and nausea after 2-3 hours, although anything over 10 can be measured in the blood.
Glad all is well though, a change means a problem has occurred so hopefully they find it!

"Shouldn't" is clearly not the same as "won't".

And on the basis it was 11 on the previous flight: suggesting that the problem is worsening, I'd be at altitude not sea level, and post Covid I'm PROB99 sure my CO tolerance is going to be worse than usual - I'm personally entirely content I made the right decision. Frustrated to miss out on some IFR practice I was looking forward to, but still content.

G