From a medical point of view I don’t think there’s another explanation for high COHb levels in Salla’s blood than receiving high doses of CO inflight. Yes, COHb will remain in the blood for quite some time after exposure, as the CO binds orders of magnitude stronger to haemoglobin than oxygen does (the reason why it is ultimately fatal…it depletes the oxygen carrying capacity of your blood) but if he had been exposed to high CO levels earlier, it would have been clinically apparent.
https://assets.publishing.service.gov.uk/media/5d53ea15e5274a42d19b6c2e/AAIB_S2-2019_N264DB.pdf
AAIB special
Mooney_Driver wrote:
Well, a lot of people who were highly critical of that pilot may end up with mud on their face now
I am – halfway – one of those… from the looks of it, I thought of this as a probable loss of control while trying to / failing to avoid IMC at night, which while not an explicit criticism of the pilot (not my style), certainly implied that the cause was a decision by the pilot.
Now it turns out that the pilot’s judgement and capability was impaired by CO (up to loss of consciousness), and this is now the most likely immediate cause.
I just consistently make two points: That while speculating about possible causes of an accident can be useful (it helps us to prevent them in our own flying), the most likely scenario (in the absence of indications of anything else) was VFR-into-IMC or similar, and (somewhat unrelated) that lack of paperwork is not the cause of an accident.
Combined with the fact that amongst all the speculation CO was not even considered, this again makes it clear that the only thing that can give the real cause is a proper investigation.
Peter wrote:
I have it from another owner (of several years’, and a diligent guy) that CO inflow is much less likely if operated pressurised.
For the Malibu:
Unpressurised, the heated air comes in “the usual way” – hot via an exhaust shroud, cold direct, and mixed in an “air box” to get the desired temperature
When pressurised, bleed air is routed into the cabin, and the bleed air (which is already hot from compression) gets heated / cooled as required in a heat exchanger.
So when pressurised, the gases from an exhaust leak cannot enter the cabin air stream.
Well, they can, if you have damage to both your heat muff and your bleed air intercooler. But it’s much more likely that they were unpressurised. There’s an OWT in the PA46 community, propagated by people trying to sell the unpressurised version (Matrix), that turning pressurisation off increases available power (it doesn’t) and that it helps climate control (it does), maybe that’s what he was aiming for.
I’m not entirely sure I agree with people who say this new accident cause relieves the pilot from criticism. This is a bit like the Courchevel discussion. The outcome is not the only thing that matters, getting away from a series of (alleged) breaches only to be (allegedly) killed by a mechanical problem doesn’t make the breaches any less serious. CO leak or not, based on what we know of the ratings the pilot held, the flight was not legal and put the pilot and passenger’s lifes at an exaggerated risk.
denopa wrote:
Well, they can, if you have damage to both your heat muff and your bleed air intercooler
Given the bleed-air is at higher pressure than the surrounding air, I don’t think that could happen while the pressurisation system is working.
In theory, CO could enter through the bleed air line via the turbo or if it makes it into the induction system somehow.
denopa wrote:
that turning pressurisation off increases available power (it doesn’t)
That’s interesting, why not?
The bleed air is still taken from the turbos, but goes out via the dump valve rather than into the cabin. That’s actually what happens all the time in the Matrix, they haven’t even removed that system!
So a bit of engine or rather turbo power is simply wasted?
Are there any other possibilities for the CO levels?
For example, if he was alive after the crash, and re-breathing air in a pocket of trapped air in the cabin, would this result in a similar reading? Or does it have to be ‘burnt air’?
Maybe there was in in-flight electrical fire? Though surely that would lead to a mayday call.
