Originally posted by snydersnapshots
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Toxic fumes in cabins and cockpits
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Originally posted by Taliesin View PostNot trying to be an ass, but it would be flowing with the pressure gradient. If you have 2 leaks, on in the high pressure turbine stage and one in the low pressure compressor, the combustion gas could flow around the outside of the case and back into the compressor, because that's the way the pressure gradient points.
The compressor makes the air flow into high pressure, that's why flow separation is an issue in the compressor, but (usually) not in the turbine
If you had a leak aft of the combustion system you'd have other indications, most notably a fire or overheat warning. We're talking EXTREMELY hot air back there. The other issue is that it would be nearly impossible for a leak as you described to flow forward to a point where it would be ingested into the engine and run through the air conditioning packs. First, the air would have to escape the engine case, which would cause fire or overheat warnings. Next, the airflow of the airplane moving through the air, as well as the flow from the fan section, would cause any airflow escaping the turbine section to move aft.
If the scenario you described was predicated on a leak in the turbine section flowing forward and entering through a leak in the compressor section, that wouldn't necessarily work either. A leak in the compressor section would be blowing air outward as well. Free flowing air from a turbine leak would not have the pressure to override the air blowing out through the leak in the compressor section. Again, the compressor section has fire loops around it as well, since any air escaping would also be extremely hot and could compromise structure in that area too.The "keep my tail out of trouble" disclaimer: Though I work in the airline industry, anything I post on here is my own speculation or opinion. Nothing I post is to be construed as "official" information from any air carrier or any other entity.
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So, in the opinion of you all who have more detailed knowledge about the inner workings of a jet engine: what is your theory on how the fumes get into the cockpit and/or cabin?
Also, if there is anybody with more information on similar incidents: are there any engine types more susceptible to the problem than others?
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Originally posted by Peter Kesternich View PostSo, in the opinion of you all who have more detailed knowledge about the inner workings of a jet engine: what is your theory on how the fumes get into the cockpit and/or cabin?
Also, if there is anybody with more information on similar incidents: are there any engine types more susceptible to the problem than others?The "keep my tail out of trouble" disclaimer: Though I work in the airline industry, anything I post on here is my own speculation or opinion. Nothing I post is to be construed as "official" information from any air carrier or any other entity.
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Originally posted by snydersnapshots View PostI may be wrong (and have been many times--just ask my wife), but it appears to me that you misinterpreted my description[...]
However, I disagree with your assessment that a leak would automatically blow air outwards and backwards. The outer case of the inner air stream is not necessarily the same as the inner case of the outer air stream.
As you can see here:http://www.aircraftenginedesign.com/...taway_high.jpg there is quite a big gap between the compressor and the bypass air duct. I still maintain the view that high pressure air getting between the two air streams and leaking back in is at least theoretically possible, it might even get into the air conditioning ducts directly, although my knowledge on those is limited at best.
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TCPs for mine.
Why? Because I've seen it a couple of times before, and in scenarios where only the pilots have been particularly affected while most in the cabin haven't noticed a thing.
Heated or pyrolized hydraulic fluid is usually the culprit - although de-icing fluid and engine preservatives (used to replace the oil during storage) have been identified too. Hydraulic fluid is nasty stuff.
A lady did a PhD on the topic not that long ago if anyone wants to know more.
I'm surprised they didn't do a full toxicology screen in the hospital to see what was affecting these guys.
One other thing...since the FO seemed to be more seriously affected than the captain, I'm thinking they should have started searching for a cause on his side of the airplane first.
If it is TCP, it seems to affect different people to a different extent. In some people it seems to cause severe immediate symptoms, while in others it causes far longer term issues. I wouldn't read too much into the different effect on the F/O vs Captain.
Also, if there is anybody with more information on similar incidents: are there any engine types more susceptible to the problem than others?
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Originally posted by Peter Kesternich View PostSo, in the opinion of you all who have more detailed knowledge about the inner workings of a jet engine: what is your theory on how the fumes get into the cockpit and/or cabin?
Also, if there is anybody with more information on similar incidents: are there any engine types more susceptible to the problem than others?
This should explain to you how the enviromental control system works in a aircraft if you were not sure at first.
http://en.wikipedia.org/wiki/Environ...stem_(aircraft)
I doubt it would be any specific engine types that has this type of problem more frequently. I've heard of issues with oil leaks and the smell getting into the cabin but that may be because of an oil leak that would get into the high or low stage which feeds the air conditioning system. Other reports of smoke it would be a fan that has burned out or some componet like the ballast from a light assembly that was breaking down internally.
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Originally posted by Taliesin View PostI quoted Gabriel's post because that's what my post refered to. I study jet engine development, so I know how an engine works (in theory) and where bleed air is taken. However, as with all things learned from books or in lectures, I lack experience in the hands-on department, where you raise some very valid points. Of course a scenario as I described would set off all kinds of bells and whistles, I was just pointing out that this was theoretically possible.
However, I disagree with your assessment that a leak would automatically blow air outwards and backwards. The outer case of the inner air stream is not necessarily the same as the inner case of the outer air stream.
As you can see here:http://www.aircraftenginedesign.com/...taway_high.jpg there is quite a big gap between the compressor and the bypass air duct. I still maintain the view that high pressure air getting between the two air streams and leaking back in is at least theoretically possible, it might even get into the air conditioning ducts directly, although my knowledge on those is limited at best.The "keep my tail out of trouble" disclaimer: Though I work in the airline industry, anything I post on here is my own speculation or opinion. Nothing I post is to be construed as "official" information from any air carrier or any other entity.
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Originally posted by Taliesin View PostHowever, I disagree with your assessment that a leak would automatically blow air outwards and backwards. The outer case of the inner air stream is not necessarily the same as the inner case of the outer air stream.
As you can see here:http://www.aircraftenginedesign.com/...taway_high.jpg there is quite a big gap between the compressor and the bypass air duct. I still maintain the view that high pressure air getting between the two air streams and leaking back in is at least theoretically possible, it might even get into the air conditioning ducts directly, although my knowledge on those is limited at best.
The gases after the combustor are indeed at a higher pressure than the gases in the compressor. And the compressor/combustor/turbine housing does connect the two.
However that housing is not sealed and is just a protective cover - it's not designed to withstand high pressure. The pressure inside it is ambient. So if a small leak occured that permitted combustion products to enter that space, those gases would just vent to the atmosphere rather than enter the compressor which would require them to be at a much higher pressure. If a large leak occured in the combustion or turbine section, that housing would either burst or more likely get burned through... and again the combustion products would vent to the atmosphere. Since the leak would be near the middle or rear of the engine and all the airflow within and around the engine is front -> rear, it seems unlikely to me that the gases could make it to the compressor inlet.Be alert! America needs more lerts.
Eric Law
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Originally posted by elaw View PostHowever that housing is not sealed and is just a protective cover - it's not designed to withstand high pressure. The pressure inside it is ambient. So if a small leak occured that permitted combustion products to enter that space, those gases would just vent to the atmosphere rather than enter the compressor which would require them to be at a much higher pressure. If a large leak occured in the combustion or turbine section, that housing would either burst or more likely get burned through... and again the combustion products would vent to the atmosphere.
But let's say this does happen, what are the chances of hot gases burning into the AC ducts and feeding into the cabin pretty much directly?
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Originally posted by elaw View PostThe gases after the combustor are indeed at a higher pressure than the gases in the compressor.
"The compressor" is in fact as mutli-stage compressor, and even the fan could be considered as the first stage. The pressure along the compressor increases from ambient before the fan (in fact beforer the inlet) to the max after the last stage, that is, just before the combustion chamber. This is the point of max pressure the air (or gasses) will ever get in a turbojet or turbofan engine. Along the combustion chamber, the subsequent turbine stages, and the nozzle, the pressure reduces until ambient again. So the pressure in the combustion chamber and the first stages of the turbine can be higher than in the first stages than the compressor, but never higher than the pressure in the last stages of the compressor.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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