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Thread: MD-80 skidded off runway at LGA

  1. #61
    Senior Member TeeVee's Avatar
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    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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    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.
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  3. #63
    Senior Member Evan's Avatar
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    Quote 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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    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.
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    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.

  6. #66
    Senior Member Gabriel's Avatar
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    Quote 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.

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  7. #67
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    Quote 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.

    http://aviation-safety.net/database/...?id=20090508-1

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    Quote 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.

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  9. #69
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    Quote 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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    Quote 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.

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  11. #71
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    Quote 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.

  12. #72
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    Quote 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.

  13. #73
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    Quote 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.

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  14. #74
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    Quote 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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    Quote 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.

  16. #76
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    Quote 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
    A thing called check / call spoilers check / call autobrakes check / call reversers in transit check / call ready reverse check / call speed call speed monitor landing performance be ready to take over if needed...

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  17. #77
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    And when, from the last 3000 landings, in 3000 of them the spoilers deployed, the mechanical reaction is to say "spoilers up" just as you did the last 3000 times. It takes a conscious effort to avoid that, a conscious effort that is well applied 99% of the times of the 0.1% of the times that the spoilers do not self-deploy (apparently including the accident subject of this thread). All in all, a very human mistake even trying to do the things well.

    Oh, pilots are humans.

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  18. #78
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    Quote Originally Posted by Gabriel View Post
    And when, from the last 3000 landings, in 3000 of them the spoilers deployed, the mechanical reaction is to say "spoilers up" just as you did the last 3000 times. It takes a conscious effort to avoid that, a conscious effort that is well applied 99% of the times of the 0.1% of the times that the spoilers do not self-deploy (apparently including the accident subject of this thread). All in all, a very human mistake even trying to do the things well.

    Oh, pilots are humans.
    The F/O in this case noticed the autospoilers were not deployed and deployed them manually. It happens. That is pilot material. I'm not referring to this accident.

    I'm sorry, but I have to draw the line somewhere. Yes, there are a number of checks involved but none of them are as critical as this ONE SIMPLE CHECK. If you have to make a conscious effort, than welcome to the adult, professional world. You are not pilot material if you can ever lose sight of the dreadful responsibility you have taken on, especially to the point where even the incredibly simple task of visually confirming the spoiler lever position is too much to ask of you. Get a sandwich job. That's one place I have to draw the line. I know that if I were a pilot I would always, religiously, check that lever upon touchdown.

  19. #79
    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    The F/O in this case noticed the autospoilers were not deployed and deployed them manually. It happens. That is pilot material. I'm not referring to this accident.

    I'm sorry, but I have to draw the line somewhere. Yes, there are a number of checks involved but none of them are as critical as this ONE SIMPLE CHECK. If you have to make a conscious effort, than welcome to the adult, professional world. You are not pilot material if you can ever lose sight of the dreadful responsibility you have taken on, especially to the point where even the incredibly simple task of visually confirming the spoiler lever position is too much to ask of you. Get a sandwich job. That's one place I have to draw the line. I know that if I were a pilot I would always, religiously, check that lever upon touchdown.
    Wonderful. But that's not how humans work. Dedicated and well trained humans applying due diligence and good will do mistakes too. The conscious effort reduce the frequency of said mistakes.

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    Talking about how humans work...
    Is it not true that pilots are not only taught to perform checklists but to also reach out and touch the item being checked ? Its certainly how my flight instructor taught me. The reasoning behind this is that when you reach out and touch something you tend to automatically look at it and notice if something is wrong. In the airline world you also have a second person checking your actions.

    In my job as a paramedic I would not only draw up a drug but would tell my crewmate what I was drawing up and show them the ampoule. I spent 34 years doing my job and knew my drugs inside out......but I still managed to make a handful of errors during those years. My failsafe crosschecks stopped the errors from progressing any further and no patient was ever put at risk....because EVEN AFTER 34 YEARS....Mistakes were possible.
    If it 'ain't broken........ Don't try to mend it !


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