Originally Posted by
Lead Balloon
Years ago I purchased a proper CO detector. I did that because my research showed that by the time those ubiquitous ‘dot’ cards stuck to the dashboard turn black, you’re likely already blacked/blacking out yourself. Further, many leaks start small - pinholes in exhaust systems that develop into cracks and other engine bay/firewall defects - and these create low CO levels in the cockpit that can nonetheless be detected by a proper CO detector before deleterious effects arise.
I was alarmed - literally - at the amount of CO that sometimes entered the aircraft during taxi, depending on wind direction and speed. And that was with windows open (in fact - that may have been the / one of the path/s of entry) and without smelling any strong exhaust smells. I’m talking levels at which protracted exposure would likely result in deleterious effects.
My eventual practise was to leave the detector switched off during taxi and take off, to avoid the distractions, and turn it on during the cruise. (The ‘off the shelf’ item did no have an on/off switch. I added that myself.) Fortunately it always read/s a big fat 0 in the cruise. I figured that the risk of a defect developing to ‘bad’ between a landing and the next taxi, take off and climb to cruise were lower than the risk arising from distractions from the alarm.
The combination of protracted exposure on the ground combined with ongoing exposure in the air due to aircraft defects? Not good. (My inexpert guess is that a pilot’s pulse rate and metabolism are running a bit faster in the initial phases of a flight than sightseeing passengers after a nice lunch...)
Modern and effective CO detectors are cheap insurance, folks.
Can I ask what aircraft type you were talking about there please?
It appears that one of the contributing factors to CO ingressing the cabin on the ground is the position of the engine exhaust relative to the ingress points, typically the windows. Typically the exhaust ports are forward of cockpit windows.
I'm struck by the exhaust configuration for the Wasp Junior on the Beaver. Many are fitted with an extension that takes the expelled gases well to the rear of the forward doors. From the photos of NOO I've seen it didn't appear to be fitted with that extension so the exhaust gases appear to be expelled on the lower starboard side pretty much adjacent to the firewall.
I was also struck by what appears to be the very well ventilated engine compartment on the Beaver. The CO poisoning was meant to have been caused by exhaust gases leaking from a crack in the collector ring and then ingressing the cabin through three open bolt holes in the firewall. I would have thought that ventilation of the engine compartment would have carried leaked gases out the opening at the rear of the cowl.
Perhaps someone with time on the DHC-2 could comment.