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  • #16
    Originally posted by Gabriel View Post
    Actually, there are 3 layers: Both airplanes were recoverable after they lifted off without flaps.
    ...a violation of QRH procedures?
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    • #17
      Originally posted by 3WE View Post
      ...a violation of QRH procedures?
      Actually no. Just follow the NEW AND IMPROVED stall and approach to stall procedures, or the NEW ANDD IMPROVED windsear procedure. (not the ones in force at the time, and I mention the windshear because it is speculated that the Northwest crew may have misidentified the situation as a windshear and was reacting accordingly, which would have been a great way to escape the situation except that they didn't do it exactly right).

      --- 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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      • #18
        Originally posted by Gabriel View Post
        Actually no. Just follow the NEW AND IMPROVED stall and approach to stall procedures, or the NEW ANDD IMPROVED windsear procedure. (not the ones in force at the time, and I mention the windshear because it is speculated that the Northwest crew may have misidentified the situation as a windshear and was reacting accordingly, which would have been a great way to escape the situation except that they didn't do it exactly right).
        What did they do wrong?

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        • #19
          Originally posted by Evan View Post
          What did they do wrong?
          You had to ask...

          Would you believe a slightly relentless pull up?
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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          • #20
            Originally posted by Evan View Post
            They managed to leave out the accident that happened three days before 2015, caused by sheer pilot ignorance and reckless procedural training.

            I think, at this point the largest threats to aviation safety are 1) Fatigue and lax training due to corporate profit-taking-induced recklessness 2) Inadequate CAA oversight and enforcement and 3) inherent vulnerabilities beyond the reach of current technologies, such as blast radius damage from an uncontained engine failure. All three of these threats can be mitigated by strict adherence to a strong safety culture that includes unwavering maintenance, training that both meets and exceeds the minimum requirements, is type-specific and exposes pilots to a deeper systems-level understanding, diligent CAA oversight and CAA enforcement penalties that are severe and costly to operators.

            The panic button should be in the voting booths.
            or in one word: re-regulation

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            • #21
              Originally posted by Evan View Post
              What did they do wrong?
              They did an excellent job modulating the elevator to keep the AoA at the onset of the stall warning, reliving back pressure every time that it started until it stopped, and pushing a bit back again when it stopped until it started. Except it was the wrong stall warning.

              The MD-80 family has a stall protection system that has 4 steps.
              1- Autoslats. If the slats are deployed to the 1st (no gap) position, they will automatically extend to full (gap) position when the plane approaches to the step 2. (irrelevant here since the slats were fully retracted)
              2- Typical stickshaker, with some margin before the critical AoA.
              3- Aural stall warning, with horns and Ms Douglas shouting STALL STALL STALL!!!! This happens at the actual critical AoA.
              4- Stick pusher.

              They were modulating around 3- instead of 2-.
              While that will give you the max lift for a given speed, but also more drag. And the worst part is that it will kill the roll damp, severely increase the aileron adverse yaw, and severely reduce the aileron effectiveness. This makes it very very hard to control the plane in roll and it becomes almost impossible to avoid PIO (unless you practice, you need to use a very different technique). They were rolling side to side up to 60 deg bank, so a good bunch of the time the lift vector was pointing more sidewise than up, and using full roll control, which implies large roll spoiler deflection, significantly increasing the drag overall.

              The onset of the stickshaker, on the other hand, helps keep the plane stable in roll (so lift points up and spoilers are not used) and has less drag (both for the lower AoA and for the lack of spoiler deflection), the plane very quickly gains a couple more knots to compensate for the very slightly lower CL compared to the critical AoA, and then keeps accelerating and climbing. Simulation showed that they would have easily and safely cleared the light pole that they hit.

              Why they did that? After interviewing other pilots of the airline (including the chief instructor), they found that there was a "tale" that, in case of windshear, it was good to pull up to the onset of the aural stall warning to get the max CL (although the procedure in place said that they stickshaker was the limit). It is speculated that they never realized about the flaps/slats issue (they never extended even the slats), and that they may have thought that they had been caught by a windshear.

              --- 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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              • #22
                Originally posted by Gabriel View Post
                They were modulating around 2- instead of 1-.
                Do you mean around 2- instead of 3- ?

                They also did a less-than-excellent job of running the before take-off checklist, which I always find amazing.

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                • #23
                  Originally posted by Evan View Post
                  Do you mean around 2- instead of 3- ?
                  No. Your flap-drag obsession is bad...other things increase drag too...like 'the back side of the drag curve'.
                  Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                  Comment


                  • #24
                    Originally posted by 3WE View Post
                    No. Your flap-drag obsession is bad...other things increase drag too...like 'the back side of the drag curve'.
                    What?

                    Slats delay airflow separation, give you some extra margin. But slats weren't being used. I think what Gabriel meant to say is that they were modulating around 3- the aural warning rather than 2- the stickshaker.

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                    • #25
                      Originally posted by Evan
                      Do you mean around 2- instead of 3- ?
                      No.

                      Originally posted by Evan
                      I think what Gabriel meant to say is that they were modulating around 3- the aural warning rather than 2- the stickshaker.
                      Yes, tank you. I corrected my post.

                      --- 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


                      • #26
                        Originally posted by Evan View Post
                        They also did a less-than-excellent job of running the before take-off checklist, which I always find amazing.
                        This happens with some frequency, low frequency but not ridiculously low.
                        With "this" I mean calling a checklist item done without actually checking the item.

                        The vast majority of the times this causes no problem because:
                        - The miscalled item was set anyway (example "Flaps? Set", nobody really looked at it while checking, but they were set anyway), or
                        - The item is not checked but it is caught at a later stage (example, second checklist, gear warning, take-off congig warning, or simply "oh, look!"), or
                        - The missing item will not cause a crash (seat belts, landing lights...).

                        There is a good reason why critical items appear in more than one checklist and/or have an independent way of confirmation (warning).

                        So you need 4 ANDs (not actually checking the called item and the negative of the the points above) to have a risk of an accident (which many times can still be avoided by flying the plane properly, like it could have been in Detroit and Madrid).

                        --- 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


                        • #27
                          Originally posted by Gabriel View Post
                          This happens with some frequency, low frequency but not ridiculously low.
                          With "this" I mean calling a checklist item done without actually checking the item.
                          I'm a huge advocate of checking off critical items by physically touching the switch or lever and following the hand with at least one eye. If I were an airline pilot, I would do this religiously.

                          There is a good reason why critical items appear in more than one checklist and/or have an independent way of confirmation (warning).
                          How many checklists does SET FLAPS appear on before takeoff?

                          So you need 4 ANDs (not actually checking the called item and the negative of the the points above) to have a risk of an accident (which many times can still be avoided by flying the plane properly, like it could have been in Detroit and Madrid).
                          You are ignoring the disorienting effect of confused situational awareness. This is why we can't expect pilots to fly out of a scenario like that. We have to prevent it from happening in the first place. Everything has to be about retaining SA.

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                          • #28
                            Originally posted by Evan View Post
                            I'm a huge advocate of checking off critical items by physically touching the switch or lever and following the hand with at least one eye. If I were an airline pilot, I would do this religiously.
                            And you would never even miss one even after ten million flights.

                            How many checklists does SET FLAPS appear on before takeoff?
                            Did you see the "or have an independent way of confirmation (warning)" part?

                            Anyway, I knew one operator of MD 80 that had it in 2: Before taxi and before take-off.

                            You are ignoring the disorienting effect of confused situational awareness. This is why we can't expect pilots to fly out of a scenario like that. We have to prevent it from happening in the first place. Everything has to be about retaining SA.
                            I am not ignoring it.

                            We can't depend on pilots flying out of that, that'w why we have pilots setting flaps, checking flaps, and take-off config warning.

                            That said, it is not needed that the pilots realize what is causing the problem. Following either the stall / approach to stall or the windshear procedures would have saved both the Northwest and Spanair flights. In any event, react to the symptom, don't ask "what is it doing now?", fly the plane, after you stabilized the situation you will have time to ask "why was it doing that?". Both these planes lifted off, meaning that they managed to create enough lift to more than balance the weight, meaning that they were able to fly. It is not like they run off the runway trying to lift off. Not stalling was all they needed to do.

                            Can we expect pilots to manage a stickshaker event? We should, but a big list of accident (including these two) show that we can't. Not reliably at least.

                            --- 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

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