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Gulfstream IV jet ran off a runway while taking off

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  • #61
    Well as far as officially ruling it out, I'll defer to the NTSB.

    But seriously... we may not be able to definitively answer that question with the information currently available.

    Here's a hypothetical (and maybe just a little far-fetched) scenario: unknown to the pilots, a passenger boards the plane with a large container of lead, and stows it in a forward baggage compartment. The plane's weight is now higher and the CG farther forward than what the pilots had calculated. Because of that, Vr now should be 165 instead of 145 knots, but the pilots don't know that.

    So they start their takeoff roll. They reach V1... then 145 knots which they think is the correct Vr, but the plane doesn't rotate. They check trim and pull back harder on the yoke but no luck. At the moment the plane reaches 164 knots, they decide there's a control problem and initiate a rejected takeoff... run off the end of the runway, crash into a ditch, and die in a fire.

    And they die never knowing that if they'd waited until the plane accelerated 1 knot more, they could have gotten airborne.
    Be alert! America needs more lerts.

    Eric Law

    Comment


    • #62
      But what about having a 'feel' for the aircraft?
      Originally posted by Gabriel View Post
      Just inventing but:
      - Pilot tries to rotate, nothing happens.
      1 sec

      But, if this is done correctly, the pilot is keeping a bit of forward pressure on the yoke up to Vr to prevent rotation. Just releasing that pressure should see a bit of rotation effect. In other words, by Vr, the thing should need no encouragement at all. Slow rotation is one thing, Pulling aft and 'nothing happens' is another. If he intends to fly he should definitely firewall the thrust right here.

      - Pilot tries harder and says "something odd with the elevator". Nothing happens.
      2 sec

      But he has just done a pre-take-off elevator check. At this point he might have considered that his initial v-speeds were wrong, but now he is maybe Vr+20 and still nothing...

      - Pilot keeps trying, adds trim, firewalls the throttles and says "Hey, help me pull up, it's an bit nose heavey", the nose roses a bit.
      3 secs

      But why does he need help? He is flying a hydraulically autuated elevator, he can see the other yoke also moving back. He can see his pitch trim. He is now at maybe Vr+30 and the thing has no positive response. Pull the plug!

      That's 3 secs but I'll give them 4 for reaction time. So perhaps they could be at 168kts after 4 secs.

      Comment


      • #63
        Originally posted by ErwinS View Post
        Could be but normally the are locked out when deployed.
        Looking at that crash scene, I doubt the reverser credit would have made much difference anyway.

        Comment


        • #64
          Originally posted by elaw View Post
          And they die never knowing that if they'd waited until the plane accelerated 1 knot more, they could have gotten airborne.
          Life is a crapshoot.

          Comment


          • #65
            Originally posted by Evan View Post
            So we can rule that out then?

            I'm thinking of Teterboro. I can't recall the details but it involved tankering which caused (or added to) a forward center of gravity that inhibited or prevented rotation. I don't recall if they rejected at that point or continued to attempt to get it off the ground before rejecting.
            I have a present for you:


            The captain was the flying pilot for the accident flight, and he stated that he
            steered the airplane onto the runway with his left hand and increased engine power for the
            takeoff with his right hand. The captain stated that, as the airplane accelerated on the
            runway, he kept his left hand on the tiller and his right hand on the power levers while the
            first officer held the control yoke. The first officer monitored the airplane’s acceleration
            and announced 80 knots and V1, and VR (11).According to the captain, as the airplane
            accelerated, he transferred first his left and then his right hand to the control yoke to
            prepare for liftoff. He stated that the airplane’s acceleration to this point had seemed
            normal and that he did not notice anything out of the ordinary when he first grasped the
            control yoke. However, airport surveillance videotapes and postaccident witness
            statements indicated that the airplane’s nose never lifted off the runway, even at an
            apparently higher-than-normal liftoff speed.
            CVR evidence indicated that, about 5 seconds after the airplane accelerated
            through the rotation speed, the captain commanded a rejected takeoff (RTO), and the CVR
            recorded sounds similar to decreasing engine power. The captain told investigators that he
            applied brakes, speed brakes, and thrust reversers in an attempt to stop the airplane and
            that all of those systems appeared to be working. The airplane was decelerating as it ran
            off the end of the runway at a ground speed of about 110 knots; through an airport perimeter
            fence; across a six-lane highway (where it struck a vehicle); and into a parking lot before
            impacting a building.. After the airplane hit the building, a
            postimpact fire ensued.

            (11) V1, the takeoff decision speed, is the maximum speed during the takeoff at which the pilot must take
            action(s) (apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop
            distance. For the accident flight, V1 was about 127 knots. VR, the rotation speed, is the speed to which an
            airplane must accelerate to become airborne when a pilot makes a control input to increase the angle of
            attack and allow the airplane to lift off the runway. The captain recalled that VR for the accident flight was
            about 133 to 134 knots. Investigators calculated it to be about 135 knots.

            The results of the simulator testing indicated that,
            for the accident conditions, even with the control column moved to its aft limit, the
            accident airplane would not have started a noticeable rotation until it reached about
            160 knots. A Bombardier performance study based on the accident airplane conditions
            estimated that the captain initiated the RTO at a speed of about 160 knots.

            A Bombardier test pilot and three other experienced airline
            transport pilots performed the simulator runs under the accident conditions. During these
            runs, the simulator pilots rejected takeoffs at various speeds (V1, VR, VR+20 knots, etc.).
            All rejected takeoffs performed in the simulator involved the immediate and aggressive
            application of reverse thrust,62 brakes, and spoilers when the RTO was initiated.
            Therefore, the deceleration performance obtained during the simulator runs was
            considered the maximum performance available from the CL-600.
            According to the study, the RTO for the accident flight was likely initiated about
            160 knots, and the airplane began to decelerate with about 2,100 feet of runway
            remaining. The study indicated that the airplane ran off the departure end of the runway at
            a ground speed of about 110 knots, penetrated the airport perimeter fence at a speed of
            about 95 knots, and was moving at a speed of about 85 knots when the FDR stopped
            recording about 70 feet from the airplane’s final resting place.
            So several things:
            This could be a copy-paste case with the accident of this thread.
            Note the Vr of 135kts and 5 seconds after that to start the RTO. That can put you very well in the range of 160+ knots. In this case, the NTSB estimates that they started the RTO at 160kts.
            Very interestingly, 160kts was also the speed at about which the plane would have been able to rotate and lift off, given the odd (irresponsible) combination of weight, CG and trim. So if the pilot had insisted with the take-off, nobody would have ever known of this accident becuase there would have been no accidnet and the pilots would have not told anybody.
            As far as we can see so far (and of course very little is known yet of the new accident), the main difference was that, in the Teterboro case, there wasn't a deep steep ditch 1000ft past the runway end. And that's why they survived, not becuase they took the "conservative" (for you) decision to abort and face a survivable crash rather than GO and play the full monty bet. Rather the contrary.

            --- 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


            • #66
              Originally posted by Gabriel View Post
              I have a present for you:




              So several things:
              This could be a copy-paste case with the accident of this thread.
              Note the Vr of 135kts and 5 seconds after that to start the RTO. That can put you very well in the range of 160+ knots. In this case, the NTSB estimates that they started the RTO at 160kts.
              Very interestingly, 160kts was also the speed at about which the plane would have been able to rotate and lift off, given the odd (irresponsible) combination of weight, CG and trim. So if the pilot had insisted with the take-off, nobody would have ever known of this accident becuase there would have been no accidnet and the pilots would have not told anybody.
              As far as we can see so far (and of course very little is known yet of the new accident), the main difference was that, in the Teterboro case, there wasn't a deep steep ditch 1000ft past the runway end. And that's why they survived, not becuase they took the "conservative" (for you) decision to abort and face a survivable crash rather than GO and play the full monty bet. Rather the contrary.
              And would they have had positive climb or would they have clipped some obstacle and come down in a populated area?

              Im not convinced RTO was the wrong move there. Certainly you dont want to crash on purpose but do you want to bring an overweight or unstable aircraft into the sky?

              Did the report fault them for the RTO?

              Comment


              • #67
                No, it didn't. Conclusion #11 on page 63:
                "The captain’s decision to initiate the rejected takeoff (RTO) was reasonable, even though the airplane had already reached a higher-than-normal RTO speed."

                In the case of that other flight, I don't think there's any way to know if the alternative (continuing the flight) would be better or worse unless you somehow could go to an alternate universe where the flight was continued and see what happens.

                If the plane was not overloaded too much and the CG was not too far forward, the flight might easily have been completed without incident. The weight problem in particular could resolve itself over time as fuel was burned. A too-far-forward CG will not make the aircraft unstable, although you could have trouble keeping the nose up on landing. But if you anticipated that problem, you could compensate by landing at a higher speed.

                All in all, an awful lot of "ifs"!
                Be alert! America needs more lerts.

                Eric Law

                Comment


                • #68
                  Originally posted by elaw View Post
                  ... how often in simulator training do you practice rejecting a takeoff after Vr? I bet the answer is either "never" or very close to never.
                  I wish I had thought of that.
                  Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                  Comment


                  • #69
                    Originally posted by Not_Karl View Post
                    Methinks you come from a lonely, but mature alternate universe. I read this post and link and for some reason feel the need to say the word Indeed. (in bold font).
                    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                    Comment


                    • #70
                      Originally posted by Evan View Post
                      And would they have had positive climb or would they have clipped some obstacle and come down in a populated area?

                      Im not convinced RTO was the wrong move there. Certainly you dont want to crash on purpose but do you want to bring an overweight or unstable aircraft into the sky?

                      Did the report fault them for the RTO?
                      No, but they said that the airplane would have rotated by 160kts (154 with full elevator travel, 170 with half elevator travel). It takes more "elevator" to rotate than to hold a climb attitude, so ability to rotate implies ability to keep flying. They had more nose-up trim available, for sure the pilot onece noticing the force needed to keep the nose up would have added more nose-up trim (that's normal in normal operations too).

                      Tha plane was barely overweight (less than 100 pounds), and the CG was quite out of range but it's already demonstrated that there was enough elevator authority.

                      The RTO was a reasonable decision because the pilot perceived and judged that the plane was unable to fly. That doesn't mean that not rejecting would not have been reasonable too. I thing that nobody would have complained if they had kept going, because nobody (but the pilots) would have known what happened to begin with.

                      --- 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


                      • #71
                        Originally posted by Gabriel View Post
                        ...The RTO was a reasonable decision...That doesn't mean that not rejecting would not have been reasonable too...
                        I fixed your font color- then added bold to make it readable.
                        Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                        Comment


                        • #72

                          --- 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


                          • #73
                            Originally posted by Gabriel View Post
                            On the one hand the video is very clear that at V1 the decision to continue has been made. But it also states that when a pilot feels that the ability of the aircraft to safely fly is in doubt an RTO after V1 is acceptable. It fails to discuss altogether the scenario where the decision to continue has been made but the aircraft won't lift off.

                            (Raised hand)...

                            At what point after V1, if the aircraft fails to lift off, should the pilot reject the takoff?

                            That question remains unanswered. Maybe because there is no sensible answer.

                            Comment


                            • #74
                              Originally posted by Evan View Post
                              (Raised hand)...

                              At what point after V1, if the aircraft fails to lift off, should the pilot reject the takoff?

                              That question remains unanswered. Maybe because there is no sensible answer.
                              I think this is the crux of the issue right here.

                              For almost every takeoff, there is a sensible answer to that question and of course it's usually to continue the takeoff.

                              But once in a blue moon, a set of circumstances arises where the pilot is called upon to make a continue/abort decision, but (s)he is unable to make the correct decision in the time allotted with the information that's available. In such cases, luck is going to determine the outcome - if there *is* a correct decision, and the pilot makes that decision by chance, all will end well. If there is a correct decision but the pilot does not choose that options, badness happens. And it's always possible there is not a correct decision. Picture some bizarre combination of failures that renders both the elevators and brakes inoperative and there's not enough runway ahead to coast to a stop: you're gonna get hurt, period.
                              Be alert! America needs more lerts.

                              Eric Law

                              Comment


                              • #75
                                Originally posted by Evan View Post
                                On the one hand the video is very clear that at V1 the decision to continue has been made. But it also states that when a pilot feels that the ability of the aircraft to safely fly is in doubt an RTO after V1 is acceptable. It fails to discuss altogether the scenario where the decision to continue has been made but the aircraft won't lift off.

                                (Raised hand)...

                                At what point after V1, if the aircraft fails to lift off, should the pilot reject the takoff?

                                That question remains unanswered. Maybe because there is no sensible answer.
                                Exactly, because whatever V1+X you define, the airplane that was reluctant to lift off at V1+X might happily lift off at V1+X+2kts.

                                I'd say that the issue is not at what speed, but given what failure.
                                If a wing is torn off, if more than engine fails, if the yoke doesn't move at all, etc... I'd say "abort".

                                That is to say, if you have made a judgement that the airplane WILL NOT fly, abort. Otherwise, go. Yes, it's a full monty bet (either you survive unscratched or you die, nothing in between), but one that you have much more chances to win.

                                Statistcally speaking, a high speed abort gives you more chances to survive than a keeping accelerating in an airplane that will not lift off. But will it not lift off? History shows that, most of the times, it will, and in that case your chances to survive are much grater than a high speed abort.

                                Of course, that history doesn't apply to both engines failing or a wing left behind on the tarmac. So in those cases, abort at whatever speed you are.

                                --- 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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