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  • #16
    Originally posted by snydersnapshots View Post
    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.
    That could be differences in how each body reacts to a given condition. It seems that it was the captain who had a lower O2 level in the blood.

    --- 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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    • #17
      Originally posted by Taliesin View Post
      Not 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
      I may be wrong (and have been many times--just ask my wife), but it appears to me that you misinterpreted my description as having the high-pressure air being taken from the turbine section. This is not the case. The high pressure bleed air is still taken from the compressor section, forward of the combustion section. Nothing is tapped off from the turbine section, with the exception of probes that measure pressure in engines that use Engine Pressure Ratio (EPR) to set power.

      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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      • #18
        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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        • #19
          Originally posted by Peter Kesternich View Post
          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?
          In my opinion, it was something from inside the airplane--a short in the wiring or something like that. If it had been coming from one of the engines, it would have affected the passengers and cabin crew too. Now, if it was from the engine, in the 737 it would be from the left side since the left pack provides air primarily to the cockpit and forward section of the cabin and the right pack primarily to the cabin. But, like I said, I think it was fumes from wiring or something burning in the cockpit area.
          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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          • #20
            Originally posted by snydersnapshots View Post
            I may be wrong (and have been many times--just ask my wife), but it appears to me that you misinterpreted my description[...]
            I 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.

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            • #21
              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.
              The tests for TCP exposure I've seen take a long time to be analysed, and only by a very few research centres. That was for suspected low-dose exposure. I'm not sure about high dose.

              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?
              The 737 has been a cause in the past. But so have a lot of other aircraft.

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              • #22
                Originally posted by Peter Kesternich View Post
                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?
                I really think it depends on the source of the smoke inside the cabin. The only reasonable explanation which would get smoke in the cabin from outside is if it was a outside source like volcanic ash (http://en.wikipedia.org/wiki/British_Airways_Flight_9) that would get into the cabin through ingestion from the engines. I found one that was due to a birdstrike (http://www.avherald.com/h?article=454a179c&opt=0) All other sources would have to be inside the cabin and is fed through the air conditioning system after the engines.

                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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                • #23
                  Originally posted by Taliesin View Post
                  I 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.
                  Ahhhh....I see what you're talking about now. Yep, I can see how a leak in the case might cause CO to get into the bleed system. The diagrams they give us are very general and not very good regarding the intricacies of the engine design.
                  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.

                  Comment


                  • #24
                    Originally posted by Taliesin View Post
                    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.
                    Your idea is correct as it stands, but is missing one important point.

                    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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                    • #25
                      Originally posted by elaw View Post
                      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.
                      Well it was just a theory
                      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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                      • #26
                        Originally posted by elaw View Post
                        The gases after the combustor are indeed at a higher pressure than the gases in the compressor.
                        Just a small correction or comment.

                        "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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