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MD-80 skidded off runway at LGA

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  • #61
    and for whatever it's worth, i snapped this as we left lga on sunday. shows quite clearly the excursion spot.

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    • #62
      Gabriel, sorry for getting "philosophical" but it hit me reading the numbers here that we put so much faith in "the numbers" and by that I mean the length of the runway, the density altitude, the performance of the engines and then make decisions based on those numbers. We count on the average professional pilot on the average day being able to operate in safety, and get an aluminum tube of our sorry azzes off the ground. Look at all of the things that had to work here right down to "X wheel revolutions" and it hit me the number of intertwined parameters that had to be satisfied for safe flight.

      I had never thought of something working or not regarding the number of times a tire went around .... kind of amazed me quite frankly.
      Live, from a grassy knoll somewhere near you.

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      • #63
        Originally posted by guamainiac View Post
        I had never thought of something working or not regarding the number of times a tire went around .... kind of amazed me quite frankly.
        It is a wierdly specific set of numbers I pulled off Aeromagazine on Boeing's website. I suppose the spin sensors have a certain requirement to function and you also don't want them to be triggered by tires spinning in the air.

        But pilots don't need to know those engineering numbers, they just need to know that procedure ALWAYS require them to confirm the autospoiler actuation once they are on the runway and to move the damned lever if they don't deploy. Which they did here. Although... if they knew the details of the system, a failure to deploy ground spoilers after touchdown might be a clue that the runway is very slick...

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        • #64
          OK let me ask you this: The crew had the auto braking set to max yet they felt no deceleration. Does auto braking rely on the same set of parameters to trigger? At this point (and I know I'm calling for speculation, for which I apologize) would you say it's looking more like a systems failure or just a really slick runway? I ask this because this event could so easily have been wife in there. She is DL crew (FA), loves the MD88/90 and in fact has already flown with a friend of one of the crew involved in this since it happened.
          Yet another AD.com convert!

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          • #65
            Evan, thanks. It's rare that we get a look at the complexity of the systems and the factors that intertwine.
            Live, from a grassy knoll somewhere near you.

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            • #66
              Originally posted by mawheatley View Post
              OK let me ask you this: The crew had the auto braking set to max yet they felt no deceleration. Does auto braking rely on the same set of parameters to trigger? At this point (and I know I'm calling for speculation, for which I apologize) would you say it's looking more like a systems failure or just a really slick runway? I ask this because this event could so easily have been wife in there. She is DL crew (FA), loves the MD88/90 and in fact has already flown with a friend of one of the crew involved in this since it happened.
              The antiskid (ABS) and I think the autobrakes too need the wheels to be spinning for technical reasons to operate. The ABS sense the wheel rotation to adjust the braking pressure and avoid or correct locking. If the wheels are locked to begin with, the ABS will never kick in in the first place. I don't know if this was corrected in latest models, but if you land already pressing the brakes with enough force to keep the wheels locked (which can be not much force to begin with if the runway is slippery), they will keep locked for the remaining of the landing roll.

              There is a number of reasons why a wheel may remain locked. Brakes applied, brakes stuck, wheel stuck, very low friction with the runway (alone or in combination with the previous reasons).

              If the runway was so slippery that the wheels didn't spin up, though, the autobrakes will not help a lot. The autobrakes don't improve traction, they just adjust brake action to achieve the desired acceleration (1, 2, 3 and 4) IF THEY CAN. There is also an aurobrakes MAX setting that will use the max braking pressure, in combination with the antiskid (autobrakes is not available without antiskid). This setting will not target a given desceleration but will brake all it can with the limit of locking, hence giving the best braking performance that is available. It will give you a very violent brake in a clean runway.

              For example, in a normal landing with autobrakes 2, the brakes will reduce the braking pressure while the reversers are applied and increase them after the reversers are closed, to keep the selected desceleration.

              If you have a smooth slippery runway with a constant low friction that, for example, cannot provide more traction than what's needed for autobrakes 1, using autobrakes 2, 3, 4 or MAX will not make any improvement over autobrake 1.

              The reason why autobrake MAX is used with slippery runway is because typically traction is not uniform along the runway, so you can profit from any part of the runway that may be not so slippery.

              --- 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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              • #67
                Originally posted by mawheatley View Post
                OK let me ask you this: The crew had the auto braking set to max yet they felt no deceleration. Does auto braking rely on the same set of parameters to trigger?
                The MD-80 autobrake is triggered by the ground spoiler activation, that is, by the speed brake lever being fully aft and latched upwards. The wheel spin-up sensors inform the autospoiler activation and that it turn informs the autobrakes. Also, only two of the four MLG spin-sensors need to be in range for that to happen.

                So, AFAIK, no ground spoiler deployment=no autobrake.

                Now... what happens when the autospoilers fail to deploy and the crew immediately selects them manually (as occurred here) BUT fails to bring the lever to the fully aft AND upwards latched position? You guessed it, spoilers retract, autobrakes never happen, loss of directional control and runway excursion.

                A McDonnell Douglas MD-90-30 plane, registered HZ-APW, sustained substantial damage in a landing accident at Riyadh-King Khalid International Airport (RUH), Saudi Arabia. All seven crew members survived. The airplane operated on a flight from Jeddah-King Abdulaziz International Airport (JED) to Riyadh-King Khalid International Airport (RUH).

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                • #68
                  Originally posted by Evan View Post
                  Now... what happens when the autospoilers fail to deploy and the crew immediately selects them manually (as occurred here) BUT fails to bring the lever to the fully aft AND upwards latched position? You guessed it, spoilers retract, autobrakes never happen, loss of directional control and runway excursion.

                  http://aviation-safety.net/database/...?id=20090508-1
                  I din't know the no spoilers = no autobrakes condition.

                  But even if correct, in this accident autobrakes would have never happened anyway because they were not armed to begin wuth.

                  --- 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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                  • #69
                    Originally posted by Gabriel View Post
                    But even if correct, in this accident autobrakes would have never happened anyway because they were not armed to begin wuth.
                    Are you talking about DL-1086 or the Saudi MD-90? The report on DL-1086 says that the 'autospoilers did not deploy' which to me implies that they were armed. In any case, if you fail to confirm the lever fully aft and latched upon landing—with your eyes on it—and fail to move it there if it isn't, you're better off being a sandwich artist.

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                    • #70
                      Originally posted by Evan View Post
                      Are you talking about DL-1086 or the Saudi MD-90?
                      Saudi. The aviation-safety.net report that you linked says that autobrakes were never armed.

                      --- 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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                      • #71
                        Originally posted by Gabriel View Post
                        Saudi. The aviation-safety.net report that you linked says that autobrakes were never armed.
                        Of course, that was the point of the Saudi 'exercise'. I added it to illustrate the effect the lack of ground spoilers has on runway manuevering. Perhaps it is possible that the F/O of DL-1086 didn't fully extend them or did it too late. There is also a 2-second lag after ground spoilers extend before autobrakes engage on the MAX setting.

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                        • #72
                          Originally posted by Evan View Post
                          ...you're better off being a sandwich artist.
                          Do we have have that condescending comment regarding a professional that might have made a brain fart than any mortal human might make?
                          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                          • #73
                            Originally posted by Evan View Post
                            Are you talking about DL-1086 or the Saudi MD-90? The report on DL-1086 says that the 'autospoilers did not deploy' which to me implies that they were armed. In any case, if you fail to confirm the lever fully aft and latched upon landing—with your eyes on it—and fail to move it there if it isn't, you're better off being a sandwich artist.
                            Sandwich artists also screw it up from time to time. And people has also died due to sandwich-makers not following the sandwich-making procedures.

                            --- 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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                            • #74
                              Originally posted by 3WE View Post
                              Do we have have that condescending comment regarding a professional that might have made a brain fart than any mortal human might make?
                              I think that well exceeds the 'brain fart' regime. As pilot-monitoring, I have one VERY CRITICAL yet incredibly simple thing to do after landing and... oops... sorry 150 souls on board, nobody's perfekt...

                              Should we talk about 'pilot material' again?

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                              • #75
                                Originally posted by Evan View Post
                                I think that well exceeds the 'brain fart' regime. As pilot-monitoring, I have one VERY CRITICAL yet incredibly simple thing to do after landing and... oops... sorry 150 souls on board, nobody's perfekt...

                                Should we talk about 'pilot material' again?
                                says the guy who's never sat in either front seat and can only monday morning, armchair everyone else into ineptitude. oh, while he has limitless hours to surf the web, comb over fcoms, qrhs, websites, accident reports, posts on other fora etc etc etc.

                                given that, it's no wonder evan is perfect and every human pilot that even thinks...is a turd.

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