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  • #16
    Originally posted by Gabriel View Post
    Even worse, the accelerometer method will pick a brake dragging a bit, less thrust than expected, or more weight than assumed, but it will not pick the above.
    Which is quite scary. Are there other instruments aboard that will pick up on it? Or, is it purely up to the observation of the crew?
    Whatever is necessary, is never unwise.

    Comment


    • #17
      Originally posted by BoeingBobby View Post
      And by the way AA you rotate at Vr not V2.
      OMG! Haha, I literally cried laughing at that. Thank you so much for catching that! LOL, well there goes my novice foot in mouth!
      Whatever is necessary, is never unwise.

      Comment


      • #18
        Now, slightly off topic - but how do you gauge the deceleration speed and/or judge a miss approach? Is it purely by feel, is it done using situtational markers or by speeds as well? I mean, you know what speed you expect when hitting the runway, but what if it's wet or there is a problem with deceleration (such as - wet conditions, or thrust reversers not responding), and you are barreling down the runway, and not stopping as well as you would like. Who calls the 'Go Around' and what effects that decision?
        Whatever is necessary, is never unwise.

        Comment


        • #19
          Originally posted by AA 1818 View Post
          All valid points - but in reality, other systems are monitoring the same thing - including both members of the cockpit crew - who have access to speed and acceleration.
          Really? How? Where?

          It's hard for me to believe that there are conditions in which the pilot simply cannot tell that he/she was not accelerating
          (Not "not accelerating". Just "not accelerating as much as it should to meet the calculated take-off performance")

          How is the pilot supposed to know if the current acceleration is the correct one? By the feel of the seat of the pants?

          --- 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


          • #20
            All valid points - but in reality, other systems are monitoring the same thing - including both members of the cockpit crew - who have access to speed and acceleration. It's hard for me to believe that there are conditions in which the pilot simply cannot tell that he/she was not accelerating, or that something was amiss and that there were no indicators from the cockpit systems.
            Actually, they don't have access to that acceleration information which is the whole reason for this thread. There is NO automatic system that warns for slow acceleration, and there is no information provided to the pilot about the expected acceleration nor actual acceleration. Feel free to be staggered by that. The boys at EK in their Melbourne incident, after they had set the incorrect thrust, had no technological way to detect their error. The pilots do not know the expected acceleration, they don't know the actual acceleration. They have the seat of their pants and their gut, which is not easy to rely on when you're operating in such a wide range of conditions. The acceleration rate they felt was probably quite normal for the A340 under different circumstances.

            Take off performance calculation and the aircraft itself are actually quite separate things. With the increase in reliance on EFB's, they will become closer over time, as we're seeing with the very latest aircraft.

            I agree with Gabriel - it would be much easier if the expected takeoff acceleration were compared by the FMC/EFB and appropriately displayed/warned in the cockpit. I was simply hypothesising about another way it could be done without aircraft technology.

            Now, slightly off topic - but how do you gauge the deceleration speed and/or judge a miss approach? Is it purely by feel, is it done using situtational markers or by speeds as well? I mean, you know what speed you expect when hitting the runway, but what if it's wet or there is a problem with deceleration (such as - wet conditions, or thrust reversers not responding), and you are barreling down the runway, and not stopping as well as you would like. Who calls the 'Go Around' and what effects that decision?
            Landing is a different kettle of fish. Once you deploy the reversers (which should be immediately) you are committed to land, so unless you have touched down very long and made a quick decision to go around, you will be committed to landing by the time you work out deceleration is not what you expected, and you're along for the ride.

            Thats why there is so much emphasis on braking action - knowing what to expect. Unfortunately that is a very imprecise science at this stage. So the answer is - by the time you know that you're not stopping, its too late to do anything other than hold on and hope...

            Comment


            • #21
              Originally posted by AA 1818 View Post
              http://www.ecfr.gov/cgi-bin/text-idx...dno=14;cc=ecfr

              From the FAA, not so made up.

              I like the way that you re-worded it though, because it does seem a little more comprehensible in that way.
              After reading it a second, third and fourth time, I noted that it's correct because it's talking about the take off distance (TOD) and accelerate to stop distance (ASD) which are calculated performance numbers, and not the distances actually available in any runway. That FAA definition is runway-independent and is sort of circular, because it defines V1 in function of the TOD and ASD which, in turn, are defined in function if V1.

              --- 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


              • #22
                Originally posted by AA 1818 View Post
                Which is quite scary. Are there other instruments aboard that will pick up on it? Or, is it purely up to the observation of the crew?
                No and neither. It's purely up to not having an engine fail at V1 exactly the day that the headwind is 10 kts slower and the ASD=ASDA and TOD=TODA.

                --- 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


                • #23
                  Originally posted by AA 1818 View Post
                  Now, slightly off topic - but how do you gauge the deceleration speed and/or judge a miss approach? Is it purely by feel, is it done using situtational markers or by speeds as well? I mean, you know what speed you expect when hitting the runway, but what if it's wet or there is a problem with deceleration (such as - wet conditions, or thrust reversers not responding), and you are barreling down the runway, and not stopping as well as you would like. Who calls the 'Go Around' and what effects that decision?
                  The difference is that the required runway length for take off is very very close to what the airplane actually needs, while the required runway length for landing has a lot of margin over what the airplane actually needs.

                  That's logical because there is more variation. In the take-off you start from a known point and a known speed (zero). The touch down point and speed are nowhere nearly as precise.

                  --- 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


                  • #24
                    Originally posted by Gabriel View Post
                    The difference is that the required runway length for take off is very very close to what the airplane actually needs, while the required runway length for landing has a lot of margin over what the airplane actually needs.

                    That's logical because there is more variation. In the take-off you start from a known point and a known speed (zero). The touch down point and speed are nowhere nearly as precise.
                    Very well explained. Thank you!
                    Whatever is necessary, is never unwise.

                    Comment


                    • #25
                      Originally posted by Gabriel View Post
                      How is the pilot supposed to know if the current acceleration is the correct one? By the feel of the seat of the pants?
                      Originally posted by MCM View Post
                      They have the seat of their pants and their gut, which is not easy to rely on when you're operating in such a wide range of conditions.
                      #irony! Haha, not making fun of the message guys - but you have to admit - there's a great irony to the statements!
                      Whatever is necessary, is never unwise.

                      Comment


                      • #26
                        Originally posted by MCM View Post
                        Actually, they don't have access to that acceleration information which is the whole reason for this thread. There is NO automatic system that warns for slow acceleration, and there is no information provided to the pilot about the expected acceleration nor actual acceleration. Feel free to be staggered by that.
                        Ahhhh! I get it now! Sorry for taking that long to come to the jump, but I understand now.

                        Originally posted by MCM View Post
                        quite normal for the A340 under different circumstances.
                        Jeezus, can you imagine the acceleration for an A340 in general? I swore the runway was never long enough at POS when BWIA's A343s were on their runs. One of the longest runways in the Caribbean and still just groaned off the ground.

                        Originally posted by MCM View Post
                        With the increase in reliance on EFB's, they will become closer over time, as we're seeing with the very latest aircraft. I agree with Gabriel - it would be much easier if the expected takeoff acceleration were compared by the FMC/EFB and appropriately displayed/warned in the cockpit. I was simply hypothesising about another way it could be done without aircraft technology.
                        So, nothing until then, which is weird... I mean, what was the recommendations/backlash after the EK incident in Australia?

                        Originally posted by MCM View Post
                        Landing is a different kettle of fish...by the time you know that you're not stopping, its too late to do anything other than hold on and hope...
                        I would like to request permission to have that as my new signature. That put one hell of a smile on my face!
                        Whatever is necessary, is never unwise.

                        Comment


                        • #27
                          Originally posted by AA 1818 View Post
                          Ahhhh! I get it now! Sorry for taking that long to come to the jump, but I understand now.
                          Not at all. 3WE's question was particularly loaded. I rather liked it which was why I bit in the first place . It only really made sense to me after reading the other thread. 3WE is far too knowledgable about these matters



                          Jeezus, can you imagine the acceleration for an A340 in general? I swore the runway was never long enough at POS when BWIA's A343s were on their runs. One of the longest runways in the Caribbean and still just groaned off the ground.
                          Ever thought that they always look like they struggled because the takeoff was always derated to ensure that was how it performed? .



                          So, nothing until then, which is weird... I mean, what was the recommendations/backlash after the EK incident in Australia?
                          Do your takeoff calculations properly, and have robust systems in place to ensure pilots do independent, separate takeoff performance. The F/O made an error, and the Captain accepted the F/O's data input when he should not have.

                          I would like to request permission to have that as my new signature. That put one hell of a smile on my face!
                          Someone is easily pleased .

                          Of course you may - but I wouldn't rely on it in an airline technical interview as the official position

                          Comment


                          • #28
                            Originally posted by MCM View Post
                            Ever thought that they always look like they struggled because the takeoff was always derated to ensure that was how it performed? .
                            Are you sure you meant "derated" and not "flexible"?
                            They are two different animals. Similar yes in that in both cases you are taking off with less than TOGA. But the intention, the method to calculate how much less thrust, and the operation of the plane during the take-off is different.

                            Flex TO // Derated TO:
                            Intention: Improve engine life, maintenance costs and reliability // Enable a take-off for which there was not enough performance with TOGA.
                            Method: Reduce thrust until either TOD=TODA or ASD=ASDA // Reduce thrust until Vmcg gets reduced to a V1 that will let you stop in the remaining runway.
                            Operation: You are free to increase thrust up to TOGA at any time, especially if an engine fails shortly after V1 // You shall not increase the thrust, especially NOT when an engine fails shortly after V1. The derated thrust is an operational limit.

                            [ref: recommendation after the accident]
                            Do your takeoff calculations properly, and have robust systems in place to ensure pilots do independent, separate takeoff performance. The F/O made an error, and the Captain accepted the F/O's data input when he should not have.
                            Not only that. The investigation used a good space of its report to analyze what resources were available to prevent such an incident after the pilots (wrongly) entered and checked the data. The answer was "none, except a very unreliable seat of the pants". The next question was what could be done about that. The answer was that the data is available in airplanes systems since the sixties (but not available for the pilots) and the idea to use that info to prevent those incidents was proposed a lot of times along the history, starting in the fifties. You can imagine the recommendation after that. Airbus is working on it (as far as I know, voluntarily because no regulation was added to require such a system or method). I don't know is Boeing is working also.

                            Shortly:
                            The actual acceleration is available and actually used by different airplane's system. And if a plane lacks this data, it would be quite easy and cheap to add it (even a $500 cellphone has 3D acceleromneters and gyros).
                            The acceleration at each speed along the take-off is nowhere in the manuals or performance charts or data, but the manufacturers have it. They need it to calculate the take-off performance. It would be extremely easy for them to get for example a value of "acceleration at 80 knots" for each take-off, in the same way that they get a TOR, TOD and ASD.
                            Such a system would have easily detected that the airplane was accelerating 28% slower in this accident.

                            --- 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


                            • #29
                              Originally posted by MCM View Post
                              Actually, they don't have access to that acceleration information which is the whole reason for this thread. There is NO automatic system that warns for slow acceleration, and there is no information provided to the pilot about the expected acceleration nor actual acceleration. Feel free to be staggered by that.
                              Thank you, because I am staggered by that. When regulators starting allowing flex take-off how could they not have seen this inherent danger? I am staggered to learn that pilots have 80kts and V1 calls but no reference check for performance itself.

                              I think your idea of a runway marker is a good one because perhaps not all a/c would have the avionics to do this internally and 20% of the discount ones that do would probably be MEL'd at the time (along with two of the lavatories). But I assume deploying this to every field across the globe would take much longer than adding the feature to every a/c operating at a flex/derated take-off thrust. The primary method could be an internal system check as Gabriel describes but a secondary check based on runway markers should be a part of it. Redundancy, redundancy, redundancy...

                              Anyway, considering a simple data entry entry error is going to have you mowing down the approach lights. I see this issue as a big hole in the proverbial cheese.

                              Comment


                              • #30
                                Gabriel, Flex is an Airbus term and has nothing to do with Boeing reduced thrust takeoff settings. I am not a "Bus" driver so I have no idea what it is. And TOGA is NOT always max thrust on takeoff. TOGA will give you what ever setting you have put in the FMS for the takeoff, be it a reduction or max. As far as the rest of this about runway markers for takeoff safety, YOU GUYS HAVE NO IDEA! IT WON'T WORK, NEVER WILL unless they start making runways as long as Edwards AFB.

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