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

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  • Gabriel
    replied
    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.

    Leave a comment:


  • Guest's Avatar
    Guest replied
    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

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

    Leave a comment:


  • 3WE
    replied
    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.

    Leave a comment:


  • Evan
    replied
    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...

    Leave a comment:


  • 3WE
    replied
    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.

    Leave a comment:


  • Guest's Avatar
    Guest replied
    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?

    Leave a comment:


  • Guest's Avatar
    Guest replied
    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?

    Leave a comment:


  • 3WE
    replied
    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”.

    Leave a comment:


  • Evan
    replied
    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.

    Leave a comment:


  • 3WE
    replied
    Originally posted by Gabriel View Post

    Happy now, [BLANK]?
    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.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by 3WE View Post
    shouldn’t you be blurting an acronym and giving a somewhat lengthy discussion about acceleration, speed and distance relationships and what constitutes reasonable assumptions?
    Speed is the integral of acceleration over time.
    Distance is the double integral of acceleration over time.
    Take-off distance calculations, and the computing of the Vee speeds, assume a given acceleration, which is based on the thrust the engines are supposed to produce, the aerodynamic drag for the configuration that the plane is supposed to have, how much the plane is supposed to weight (mass), the assumption that the pilots will not be riding on the brakes (or have partial parking brakes applied), assumed runway slope, etc. A lot of supposed and assumed.

    Planes (important ones) already measure acceleration so they could easily check, say at 60 knots, if the plane i accelerating as it was assumed during the take-off performance calculation. Hence TOPMS (Take Off Performance Monitoring System). Easy stuff.

    Then you can mix that with aerodynamic data (the ground acceleration will not tell you that you are taking off with a 5 knots tailwind and not the 15 knots headwind you were supposed to have) and with GPS and runway map (nothing of the above will detect you taking off from the wrong intersection, or the wrong runway) to create the eTOPMS (e for enhanced).

    Happy now, [BLANK]?

    Leave a comment:


  • 3WE
    replied
    Originally posted by Groot View Post
    If you travel at a certain speed for a certain amount of time become a distance...
    As long as you are certain

    Originally posted by Groot
    Basic physic, right?
    With one caveat and a few moderately important assumptions.

    Originally posted by Groot
    We are pretty much all right...
    Indeed, these types of crashes don’t happen that often.

    Originally posted by Groot
    […]

    Or what shall I do ?

    I am opened to suggestions
    Gabriel has one he’s mentioned before, with some moderately strong emphasis.

    I did toy with the idea of an app for a smartphone or some sort of computerized, trend-tracking warning light.

    Leave a comment:


  • Guest's Avatar
    Guest replied
    Originally posted by 3WE View Post

    So it’s not a distance?

    And I may be a blank Gabriel, but shouldn’t you be blurting an acronym and giving a somewhat lengthy discussion about acceleration, speed and distance relationships and what constitutes reasonable assumptions?
    If you travel at a certain speed for a certain amount of time become a distance...

    Basic physic, right?

    We are pretty much all right...

    But they told me to focus on a speed not to look for a distance before take-off when looking for a V1 and VR.

    Or what shall I do ?

    I am opened to suggestions

    Leave a comment:


  • BoeingBobby
    replied
    Originally posted by LH-B744 View Post

    Ahm. I am hopefully allowed to be offtopic for one minute.

    And now, back on topic.
    Now THAT is funny! You have NEVER been on topic once!

    Leave a comment:


  • 3WE
    replied
    Originally posted by gurrit View Post
    But calculated as a speed... We look at a speed
    So it’s not a distance?

    And I may be a blank Gabriel, but shouldn’t you be blurting an acronym and giving a somewhat lengthy discussion about acceleration, speed and distance relationships and what constitutes reasonable assumptions?

    Leave a comment:

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