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MD-87 hits fence after takeoff from TME. All passengers survive the crash.

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  • #31
    Originally posted by Gabriel View Post
    the assumption that the pilots will not be riding on the brakes (or have partial parking brakes applied)
    Or full manual panic brakes applied while the pilot flying is going TOGA and trying to rotate... Yes. We shouldn't assume that.

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    • #32
      Originally posted by Evan View Post

      Or full manual panic brakes applied while the pilot flying is going TOGA and trying to rotate... Yes. We shouldn't assume that.
      Well, weshould probably wait for the final report instead of assuming “stupid pilots”.
      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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      • #33
        Originally posted by 3WE View Post

        Aggie Summary Statements (possible repetition of Gabellian aeroengineerspeak):

        Because this involves acceleration, there can be compounding effects. (Is that important, Gabriel?)

        So we assume that actual acceleration is close to what it should be.

        We assume our safety buffers are adequate.

        We assume the weather doesn’t throw big curve balls.

        We assume that good data and calculations are used/made.

        (And probably a couple more.)

        By the way, 3BS is now in violation for multiple misuses of “we” and I anticipate appropriate physical, public punishment along with admonishment from Bobby, ATL and Kent.

        I will be happy when said punishment is administered.
        Ah, there is a we rules limitations?

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        • #34
          Originally posted by Evan View Post

          Or full manual panic brakes applied while the pilot flying is going TOGA and trying to rotate... Yes. We shouldn't assume that.
          What is the reason to apply parking brake when you have the brakes working? Because they were working or there was a problem too?

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          • #35
            Originally posted by gurrit View Post

            Ah, there is a we rules limitations?
            Those of us here, who are not airline pilots, are often overly bold on what “we” should do in the industry…as if we are part of it, which we are not.

            Thanks for playing along on the subject of V-1, messed up takeoffs and what pilots SHOULD do and how “we” would have done better (moderate sarcasm).

            The subject is beaten to death every year or so.

            I still ponder how we avoid the situation where acceleration is a little bit slow, and you hit V-1 at an extra long distance.
            Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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            • #36
              Originally posted by 3WE View Post

              Those of us here, who are not airline pilots, are often overly bold on what “we”!should do in the industry…as if we are part of it, which we are not.
              Not only are those of here, who are not airline pilots, part of the industry, we are the most important part of the industry. Some of us here, who are not pilots, are boldly concerned about those of us who are pilots, or mechanics, or regulators, or airframers. It's as if our lives depend on it...

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              • #37
                Originally posted by Evan View Post

                Not only are those of here, who are not airline pilots, part of the industry, we are the most important part of the industry. Some of us here, who are not pilots, are boldly concerned about those of us who are pilots, or mechanics, or regulators, or airframers. It's as if our lives depend on it...
                Indeed.

                Then, again, I know of a lot of agricultural ankle biters.
                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                • #38
                  Originally posted by 3WE View Post

                  Those of us here, who are not airline pilots, are often overly bold on what “we” should do in the industry…as if we are part of it, which we are not.

                  Thanks for playing along on the subject of V-1, messed up takeoffs and what pilots SHOULD do and how “we” would have done better (moderate sarcasm).

                  The subject is beaten to death every year or so.

                  I still ponder how we avoid the situation where acceleration is a little bit slow, and you hit V-1 at an extra long distance.
                  Ahhhhhh, you are not a pilot so when we use a technical word like V and 1 you get lost.

                  Ah, sorry I did not know you were mainly on the ground.

                  It was not done on purpose...

                  But if you like I can talk about... Sorry, "W-E" can talk about the V2 case scenario, in case he was going to rotate and how a MD-80 can look for V2+10kts

                  ))))))))))))))))))))))))))))))))))))))))

                  Comment


                  • #39
                    Originally posted by 3WE View Post
                    The subject is beaten to death every year or so.
                    I still ponder how we avoid the situation where acceleration is a little bit slow, and you hit V-1 at an extra long distance.
                    That's not the main problem. V1 is only relevant in an engine failure scenario (ok, some other rejected take-off scenarios too).

                    The REAL problem we discussed while beating this dead horse dead again and again is what happens when you DO NOT reject the take off, which is what (almost) ALWAYS happens in the accidents and incidents involving a sub-par take-off scenario. So Vr is the problem.

                    So say for example that you mixed up 2 numbers and instead of calculating the take off with your actual weight of 53000 lb you input 35000 lb.

                    Now you get a given Vr and a given distance, and with that Vr comes a Vlo (lift-off) which is not shown to the pilot but is part of the "internal" algorithm.
                    Is your filed length is more than the minimum needed, V1 is selectable within a range that ensures that you can reject at V1 and stop, or lose an engine at V1 and lift off, both within the the runway length (which is why Vlo is part of the internal algorithm).
                    Vr is NOT selectable. Is unique for each scenario. And a unique Vlo and lift-off distance comes with it.

                    But the acceleration will be 35/53=66% of the assumed one.
                    And, to make things worse, to generate a lift equal to the increased weight you will need a speed sqrt(53/35)= 1.23 the calculated speed

                    Since the distance needed to achieve a given speed is given by D = V^2 / 2A, we can write the assumed and real scenarios as

                    Assumed: D1 = V1^2 /2A1
                    Real: D2 = V2^2 / 2A2 = (1.23V1)^2 / 2(0.66A1) = 2.29 * V1^2 / 2A1 = 2.3 D1

                    The real distance you will need to get the plane in the air is more than twice what you thought it would take.

                    And there is NOTHING to alert you that you are accelerating less than expected and will need more speed and much more distance than expected.

                    Good luck.

                    --- 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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                    • #40
                      Originally posted by Gabriel View Post

                      ***there is NOTHING to alert you that you are accelerating less than expected and will need more speed and much more distance than expected.***
                      Nothing? Not even playing the “absolute game”: Bobby has two things* (actually many more things) and ATL has a secret system of checking something.

                      *Left and right buttocks, (and many takeoffs resulting in a good, albeit fallible, system of checks…)
                      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                      Comment


                      • #41
                        Originally posted by Gabriel View Post
                        That's not the main problem. V1 is only relevant in an engine failure scenario (ok, some other rejected take-off scenarios too).

                        The REAL problem we discussed while beating this dead horse dead again and again is what happens when you DO NOT reject the take off, which is what (almost) ALWAYS happens in the accidents and incidents involving a sub-par take-off scenario. So Vr is the problem.

                        So say for example that you mixed up 2 numbers and instead of calculating the take off with your actual weight of 53000 lb you input 35000 lb.

                        Now you get a given Vr and a given distance, and with that Vr comes a Vlo (lift-off) which is not shown to the pilot but is part of the "internal" algorithm.
                        Is your filed length is more than the minimum needed, V1 is selectable within a range that ensures that you can reject at V1 and stop, or lose an engine at V1 and lift off, both within the the runway length (which is why Vlo is part of the internal algorithm).
                        Vr is NOT selectable. Is unique for each scenario. And a unique Vlo and lift-off distance comes with it.

                        But the acceleration will be 35/53=66% of the assumed one.
                        And, to make things worse, to generate a lift equal to the increased weight you will need a speed sqrt(53/35)= 1.23 the calculated speed

                        Since the distance needed to achieve a given speed is given by D = V^2 / 2A, we can write the assumed and real scenarios as

                        Assumed: D1 = V1^2 /2A1
                        Real: D2 = V2^2 / 2A2 = (1.23V1)^2 / 2(0.66A1) = 2.29 * V1^2 / 2A1 = 2.3 D1

                        The real distance you will need to get the plane in the air is more than twice what you thought it would take.

                        And there is NOTHING to alert you that you are accelerating less than expected and will need more speed and much more distance than expected.

                        Good luck.
                        Ih, ih, ih you are taking personally.

                        Fiiiinnnnneee, "W-E" do not talk anymore about V...

                        Happy?

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                        • #42
                          Originally posted by gurrit View Post
                          Fiiiinnnnneee, "W-E" do not talk anymore about V...
                          I think you will find it mildly amusing that we once proposed V-3BS: The speed at which you can still reject a takeoff, run off the end and have a probably-survivable crash.

                          It appears to have worked well in this incident.

                          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                          Comment


                          • #43
                            Originally posted by Gabriel View Post
                            That's not the main problem. V1 is only relevant in an engine failure scenario (ok, some other rejected take-off scenarios too.
                            The Horse That Wouldn’t Die

                            I realize that you are being academic here but as I pointed out at the beginning, a private MD-87 with 18 souls aboard is probably not overweight (or an underweight weight calc error). Also, a good indicator of degraded acceleration is found on the engine instruments which almost certainly were complaining about the #1 parameters. It’s possible that these were not being monitored (and there’s your pilot error) and perhaps the yaw isn’t very noticeable on fuselage-mounted engines. I can’t fathom any other reason for them not stopping safely at low speed.

                            I think V3bs is irrelevant here. The old argument about when to give up when you decide to continue at V1 but she won’t rotate at Vr doesn't matter if you never make it to Vr.

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                            • #44
                              Out of popcorn, I'll be back in a few. ​​​​​​

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                              • #45
                                The only thing missing from this discussion is our German friends explanation of how Randazos flight sim reacts to the infamous V1 cut.

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