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*Another* pilot incapacitated due to pressurization problems?

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  • #31
    Originally posted by Gabriel View Post
    Oh, well. It seems that a red line in the dial would qualify after all as per b-6) (however stupid that is), because issue d clarifies:

    So the real warning ("the sign that warns", according to the above) is not required if the plane is not certified for operation above 45,000ft, which the TBM likely wasn't.
    According to smartcockpit.com, the TBMs do, in fact, have a "CABIN PRESS" warning light, for which there is even a test switch on the Pressurization panel. FWIW, the light is amber, not red.

    It bears keeping in mind that as of now there is no way to know whether the "problem" the pilot reported to ATC was a pressurization one or some other one, and the pressurization one developed subsequently.

    Comment


    • #32
      Originally posted by Gabriel View Post
      Oh, well. It seems that a red line in the dial would qualify after all as per b-6) (however stupid that is), because issue d clarifies:

      (d) If certification for operation above 45,000 feet and not more than 51,000 feet is requested—

      (4) In addition to the cabin altitude indicating means in (b)(6) of this section, an aural or visual signal must be provided to warn the flight crew when the cabin pressure altitude exceeds 10,000 feet.

      So the real warning ("the sign that warns", according to the above) is not required if the plane is not certified for operation above 45,000ft, which the TBM likely wasn't.
      There is no cabin altitude selection on the TBM-900. The system (new to the TBM-900) is entirely controller by a microprocessor. The only pilot selectable options are AUTO and MAX DIFF (for minimum cabin altitude). The system controls the outflow valve (there is a guarded DUMP switch but it is inhibited above 14,000ft).

      There is a cabin altitude 'warning' in the form of two passive ECAM-style messages on an anunciator window (#6 on the attached image): CABIN ALTITUDE and CABIN DIFF PRESSURE in a small box on the center MDU. The anunciation is in red but can easily be overlooked in a sea of display data—especially if the pilot is distracted by another indication problem. There is also an amber CPCS BACK UP MODE message if a system prevents it from computing the optimum cabin altitude, in which case the cabin altitude is set at 9800ft.

      There is supplemental O2 of course. The pax masks will drop automatically ONLY if the O2 switch is in the ON position.

      EDIT: I THINK that a red MDU message is accompanied by a master warning alarm.

      Comment


      • #33
        The scenario I can envisage is a transient loss of power due to an engine malfunction (or icing or damage) where the pilot is distracted by the issue and does not notice the dropping bleed air pressure and diminishing cabin pressure differential. There is a ram air backup (mainly for smoke removal) but it must be manually selected. So, as the cabin altitude gadually rises, cognitive function starts to become impaired. Eventually a master warning comes on but the pilot might associate that with the engine issue and there might be other messages on the MDU to support that conclusion, especially in an impaired state of mind. If the O2 switch is not in the ON position, there will be no indication from O2 mask deployment either.

        If this scenario is accurate, my parlour-talking recommendations would be:

        When cabin pressure cannot be maintained by the bleed air system:

        - the system automatically switches to a ram air/OFV closed configuration
        - the O2 system has only AUTO and OFF settings and becomes AUTO (masks deploy).

        Comment


        • #34
          The scenario I can envisage is a transient loss of power due to an engine malfunction (or icing or damage) where the pilot is distracted by the issue and does not notice the dropping bleed air pressure and diminishing cabin pressure differential. There is a ram air backup (mainly for smoke removal) but it must be manually selected. So, as the cabin altitude gadually rises, cognitive function starts to become impaired. Eventually a master warning comes on but the pilot might associate that with the engine issue and there might be other messages on the MDU to support that conclusion, especially in an impaired state of mind.
          If such master warning exists, it should trigger at a cabin altitude that is steel well breathable, so no hypoxic impaired state of mind should have be present by then.

          If this scenario is accurate, my parlour-talking recommendations would be:

          When cabin pressure cannot be maintained by the bleed air system:

          - the system automatically switches to a ram air/OFV closed configuration
          Does ram air has the potential to provide any significan pressurization at high altitude? I doubt it. The max possible pressure that you can get from direct ram air is the dynamic pressure, 1/2*D*V^2
          D = air density
          V = true airspeed

          With the air density at 28000ft and taking 330KTAS for V, this gives a dynamic pressure of about 0.07t atmospheres, not much when the pressure up there is 0.33 atm, so the "ram-air pressurized" cabin altitude would be some 0.40 atm (as a reference, the density at 12000ft, which is usually taken as the limit where you can suffer no mental impairment even after long exposures, is 0.64 atm)

          - the O2 system has only AUTO and OFF settings and becomes AUTO (masks deploy).
          Well, my parlour-talking recommendation would be:

          a) For any pressurized plane that is certified for flight above 12000ft:
          (1) There must be a celar aural AND visual warning that activelly calls the attention of the pilot to the cabin altitude indication the moment said cabin altitude exceeds 10,000ft ISA,
          (2) The visual warning must be red or amber and clearly visible in the main instrument panel or other place in the direct field of view of the pilot. Lines or marks in an indicator don't qualify, and a light in the pressurization panel doesn't qualify eiother unless said panel is in the direct field of view of the pilot.

          That is very easy and inexpensive to implement during airplane design, and I bet that it would be very easy even as a retrofit. A simple, stand alone pressure probe with a light and horn calibrated to trigger at 20.6 mmHg (that's the pressure at 10000ft ISA). It doesn't need to be connected to any system but the electric system and it doesn't need any data from any other airplane's system.

          I can't believe you are good to certify a plane for 44900ft without such an active warning. As Evan said, the supplemental O2 is of no use if the pilot is not aware tha he needs it, and by when he is aware his judgement and reasoning is too impaired to take possitive action.

          The FAA needs to have this fixed... like yestereday.

          --- 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 ---

          Comment


          • #35
            Originally posted by Gabriel View Post
            Does ram air has the potential to provide any significan pressurization at high altitude? I doubt it.
            Not as a primary means but possibly as a redundant emergency measure. I am just pointing out that, in the absence of any redundancy, there is one solution that might only require a bit of software and might provide a few extra critical minutes of cognitive state. I've found a couple of patents on the idea ( http://www.google.com/patents/US3101918 ) The DC-8, you might recall, used a ram air intake but along with a turbocompressor driven by bleed air.

            If ram air could augment a bleed air drop in pressure then it might make the difference. The TBM-900 has a redundant bleed air intake port if the primary one is not performing correctly. The switchover is automated and I don't think the pilot has any awareness of it or control over it. But, of course, if the turbine compressor itself is not performing well, this is not redundancy.

            The FAA needs to have this fixed... like yestereday.
            Maybe this is one of those areas where industry acts without having to because I think most if not all pressurized a/c flying below 45,000 have audible warnings for cabin pressure. As I added above, I'm pretty sure the TBM-900 provides a master warning (front and center above the PFD) with any red "ECAM" style message. Of course that only adds to the mystery here....

            But then a master warning can be misinterpreted when other problems exist. If you are working a power issue and the red light comes on you might have a tendency to silence it and remain focused on that problem.

            Comment


            • #36
              In 1961, Boeing applied for ram-air emergency cabin pressure provision. Read this: http://www.freepatentsonline.com/3101918.pdf

              Notice the charts for decompression time and decompression time with cabin inflow. It seems to provide about 45 seconds more reaction time and a quicker reduction in cabin altitude during an emergency descent.

              Comment


              • #37
                Actually... notice those charts assume a problem occurring while the aircraft is cruising at *70,000* feet altitude!

                Looking at the very last chart, it appears the ram air scoop could provide a 10,000 ft. cabin altitude at about 30,000 feet. Of course it makes no mention of airspeed which would be a big factor. Given the cruising altitude and the appearance of the nose of the example aircraft (for what that's worth), they may be thinking supersonic.
                Be alert! America needs more lerts.

                Eric Law

                Comment


                • #38
                  Originally posted by elaw View Post
                  Actually... notice those charts assume a problem occurring while the aircraft is cruising at *70,000* feet altitude!

                  Looking at the very last chart, it appears the ram air scoop could provide a 10,000 ft. cabin altitude at about 30,000 feet. Of course it makes no mention of airspeed which would be a big factor. Given the cruising altitude and the appearance of the nose of the example aircraft (for what that's worth), they may be thinking supersonic.
                  No doubt, apples and oranges. But those are also 'blowout' scenarios. Perhaps a bit of ram air could make up for a partial loss of bleed air pressure experienced due to a malfunction. Perhaps not.

                  Comment


                  • #39
                    Originally posted by Evan View Post
                    Not as a primary means but possibly as a redundant emergency measure. I am just pointing out that, in the absence of any redundancy, there is one solution that might only require a bit of software and might provide a few extra critical minutes of cognitive state. I've found a couple of patents on the idea ( http://www.google.com/patents/US3101918 ) The DC-8, you might recall, used a ram air intake but along with a turbocompressor driven by bleed air.
                    Yes, that's why I've said "direct ram air".
                    You can have a RAT that drives a compressor, and if the RAT is big enough you can provide any pressurization level you want.

                    If ram air could augment a bleed air drop in pressure then it might make the difference.
                    That is the problem: Direct RAM air cannot supplement just a drop in pressure. As long as the cabin differential pressure is bigger than the dynamic pressure, the RAM air intake will be in fact an exhaust, just accelerating the decompression.

                    If the cabin differential pressure drops below the dynamic pressure, then the RAM air can start to help. But the cabin altitude will be too high by then if the plane is flying at high altitude.

                    I say, forget this kind of help. If you have problems with the pressurization:
                    1- Have a warning that immediately, actively, unmistakably and unignorably warns you of that situation.
                    2- Immediately don O2 masks.
                    3- Descend.
                    4- Call ATC.

                    --- 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 ---

                    Comment


                    • #40
                      Originally posted by Evan View Post
                      In 1961, Boeing applied for ram-air emergency cabin pressure provision. Read this: http://www.freepatentsonline.com/3101918.pdf

                      Notice the charts for decompression time and decompression time with cabin inflow. It seems to provide about 45 seconds more reaction time and a quicker reduction in cabin altitude during an emergency descent.
                      Yes,
                      If you are at 70,000ft and Mach 1.4, and suffer an explosive decompression, the cabin altitude will not go so high as 70,000ft where the air pressure is 0.04 atm, but will instead remain at just 30,000ft where the air pressure will be as much as 0.30 atm (I have no idea how will do to increase the ambient pressure in 0.26 atm using ram air that will have a dynamic pressure of just 0.09atm, in fact I do know: they won't). That's good:
                      Your body fluids will not boil.
                      You can sustain breething with 100% O2 (what you can't do with a cabin altitude above 42000ft).
                      Your TUC will increase from about 10 seconds to about 25 seconds.

                      A few questions:
                      How will they do to get more more pressure than the potential pressure the air has? (because that's the dynamic pressure, potential pressure that realizes only if you losslessly slow it down to zero). Answer: they won't
                      How do they do to open a hole that connects the cabin to a point where the pressure (including dynamic pressure) is much lower than that in the cabin, and the depressurization rate slows down instead of increasing? Answer: Tehy don't.
                      Did you know that patents don't need to be technically correct? That things that violate the first, second, or both principles of the Thermodynamics have been patented? Repeatedly? A patent is not a peer-reviewed scientific or technical paper.
                      Have you ever seen a direct ram air pressurization system installed in an airplane?
                      Can we please return to a TBM flying at 28000ft and 330kts (M 0.55)?

                      --- 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 ---

                      Comment


                      • #41
                        Originally posted by Evan View Post
                        No doubt, apples and oranges. But those are also 'blowout' scenarios. Perhaps a bit of ram air could make up for a partial loss of bleed air pressure experienced due to a malfunction. Perhaps not.
                        Evan, for the last time:
                        If you open a hole in the fuselage and the pressure inside is higher than outside (including the dynamic pressure), air will go out, not come in.

                        Is this that hard to understand really?

                        --- 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 ---

                        Comment


                        • #42
                          Originally posted by Gabriel View Post
                          Evan, for the last time:
                          If you open a hole in the fuselage and the pressure inside is higher than outside (including the dynamic pressure), air will go out, not come in.

                          Is this that hard to understand really?
                          I would expect it to be valved to prevent egress, so if the cabin pressure differential at a cabin altitude of, say, 15000 ft is of greater force than the pressure of a 330kt airstream at 28,000ft, then it would be of no benefit. You're the engineer here. (as I originally said, the ram-air on the TBM-900 is for cabin ventilation only. In the absence of sufficient bleed air I thought it might be of some benefit but obviously not if the physics work against it.)

                          But then we are back once again to a cabin pressurization system dependent on the bleed air from a single engine without impaired-performance redundancy.
                          Can we please return to a TBM flying at 28000ft and 330kts (M 0.55)?
                          Certainly.

                          The key to this mystery is the request for 18,000 instead of 10,000. I'm beginning to think the pilot DID see the cabin altitude warning and interpreted this as a performance issue with the bleed air rather than an outright failure—thinking that he must get down to an altitude where the system can maintain the proper cabin altitude but also where he can still make his destination without a technical stopover—and failed to understand the rapid onset nature of hypoxia.

                          This may be supported by the TBM-900 QRH procedure, the last two items are, in this order (my bolding):

                          6 - Limit flight altitude to maintain cabin altitude < 10000 ft
                          7 - If necessary . . . . . . . . . . . . . . . . . . EMERGENCY DESCENT

                          So perhaps he was on step 6 and never made it to step 7.

                          AFAIK, there is an indication of cabin vertical speed and cabin pressure differential but no indication of actual cabin altitude (which is controlled by the system).

                          Comment


                          • #43
                            Originally posted by Evan View Post
                            But then we are back once again to a cabin pressurization system dependent on the bleed air from a single engine without impaired-performance redundancy.
                            A lot of "back ups" are replaced by "paln Bs" in any single-engine airplane even before starting to mess with the pressurization.

                            The key to this mystery is the request for 18,000 instead of 10,000. I'm beginning to think the pilot DID see the cabin altitude warning and interpreted this as a performance issue with the bleed air rather than an outright failure—thinking that he must get down to an altitude where the system can maintain the proper cabin altitude but also where he can still make his destination without a technical stopover—and failed to understand the rapid onset nature of hypoxia.

                            This may be supported by the TBM-900 QRH procedure, the last two items are, in this order (my bolding):

                            6 - Limit flight altitude to maintain cabin altitude < 10000 ft
                            7 - If necessary . . . . . . . . . . . . . . . . . . EMERGENCY DESCENT

                            So perhaps he was on step 6 and never made it to step 7.

                            AFAIK, there is an indication of cabin vertical speed and cabin pressure differential but no indication of actual cabin altitude (which is controlled by the system).
                            Well, the warning is triggered by the cabin altitude exceeding 10,000ft.
                            Maybe... big maybe... he thought that with 18000ft he would be able to hold a cabin altitude of 10000ft. We will never know.

                            But even in that case, since the cabin altitude was already above 10000ft, he should have gone for step 7.

                            Oh, and by the way, I'm quite sure that there is a cabin altitude indicator. It is required by the FARs.

                            Since it seems that you have access to these checklists, can you please tell us the title of that checklist (I want to know if it's the response to the cabin altitude warning or to inability to control the cabin altitude, which are related but two different things. It's strange for me that "emergency descent" comes in a step 7 in a situation where the cabin altitude could be 28000 ft or perhaps higher (whatever is the airplane's ceiling).

                            --- 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 ---

                            Comment


                            • #44
                              Originally posted by Gabriel View Post
                              Oh, and by the way, I'm quite sure that there is a cabin altitude indicator. It is required by the FARs.
                              This is also pointed out in the manual but there is nothing describing a cabin altitude display (there is description of a cabin vertical speed and pressure differential display however).

                              Since it seems that you have access to these checklists, can you please tell us the title of that checklist (I want to know if it's the response to the cabin altitude warning or to inability to control the cabin altitude, which are related but two different things. It's strange for me that "emergency descent" comes in a step 7 in a situation where the cabin altitude could be 28000 ft or perhaps higher (whatever is the airplane's ceiling).
                              I think the TBM-900 ceiling is around 31,000ft. The title of the checklist is "CABIN ALTITUDE", referring to the warning message/master warning event.

                              I can't recall where I downloaded this but perhaps I can PM it to you. Can I send a 6.2MB attachment?

                              Comment


                              • #45
                                ahh, nevermind, it's here: http://www.tbm850.com/2014/images/tb...PIM_900R01.pdf

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