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V1 is or is not a LOCATION on the runway...

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  • Thank you for that, Evan. It answeres my question very nicely.

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    • Originally posted by BoeingBobby View Post
      I have been called a fat ass, a wise ass, a dumb ass and a smart ass. My wife has called me a lazy ass and a lard ass. But I have never been told that I have an ass that excels!
      Liar

      You are an ATP. That requires excellent technical skills as well as outstanding seat of the pants flying.

      You have been told that after countless check rides.
      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

      Comment


      • I've not been following this thread in detail so maybe this is old news but both Honeywell and Airbus are developing runway awareness systems that indicate the V1 point on the runway. The Honywell system (Smart Runway) uses accelerometers and a runway data base. See Aviation Week for December 16, page 45. Hneywell has one airline signed up as a customer.

        Also at http://www.aviationweek.com/Article....644762.xml&p=2

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        • And we have not even thought of this other failure mode.
          Like in other cases (headwind much lower than reported), a take-off acceleration measurement per-se will not be enough though. It would need to compare the acceleration with the needed lift-off speed and runway available.

          The crew of a Belair Airbus A320-200, registration HB-IOP performing flight 4T-2532 from Basel/Mulhouse (Switzerland/France) to Djerba (Tunisia) with 144 people on board, prepared for a full length departure from Basel's runway 15, however, subsequently lined up runway 15 from taxiway G, about 1500 meters/4930 feet down the runway leaving 2400 meters/7870 feet of takeoff distance available remaining, and took off. The aircraft became airborne before the end of the runway and continued to Djerba for a safe landing.

          On Dec 9th 2014 the French BEA reported in their weekly bulletin, that the takeoff was performed with the power setting for the full length departure although the aircraft entered the runway at taxiway G. The occurrence was rated a serious incident and is being investigation by Switzerland's SUST.

          http://avherald.com/h?article=47e8b382&opt=0

          When will we have a(n other) total air disaster because of this? It's just a matter of time.

          --- 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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          • I'm confused !
            They planned for a full length departure so did that mean that they previously calculated a NEED for that much runway ? If that is so why did they accept the intersection departure ?

            When I was SCUBA diving we had a saying... "plan the dive, dive the plan"

            Surely the same applies to aviation ?

            "Plan the flight, fly the plan"

            An old, wise, very experienced flight instructor used to say to me..... "Spare runway length behind you.....isn't runway ! It's unused tarmac that could be runway !"
            Apparently the crew took off with the power settings that were calculated for the full length takeoff and still managed to get airborne before the end of the runway. So surely, this means that their calculations were wrong in the first place ?
            If it 'ain't broken........ Don't try to mend it !

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            • All well and good, but intersection take offs happen and happen with airliners too. In the vast majority of the cases the pilots have calculated that the takeoff is possible with safety margins. And what's the difference between departing Chicago midway or from the middle of a 14000 ft runway at O'hare?

              There's a little loop hole in the Swiss cheese but Boeing Bobbys butt has it covered.
              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

              Comment


              • Originally posted by brianw999 View Post
                I'm confused !
                They planned for a full length departure so did that mean that they previously calculated a NEED for that much runway ? If that is so why did they accept the intersection departure ?
                Probably not. Many times the runway available is longer than needed and the planes still take off from the beginning of the runway. In those cases pilots will typically compute and use a reduced take-off thrust that is lower than the nominal engine take-off thrust.

                When I was SCUBA diving we had a saying... "plan the dive, dive the plan"

                Surely the same applies to aviation ?

                "Plan the flight, fly the plan"
                Well, yes but, I don't know in Scuba, but in aviation many times you have to change the plan. In that case the key is to actually make the new plan before executing it!


                An old, wise, very experienced flight instructor used to say to me..... "Spare runway length behind you.....isn't runway ! It's unused tarmac that could be runway !"
                The three most useless things in aviation:
                The runway behind.
                The air above.
                The empty space in the tanks (although this last one is highly disputed lately)

                Apparently the crew took off with the power settings that were calculated for the full length takeoff and still managed to get airborne before the end of the runway. So surely, this means that their calculations were wrong in the first place ?
                Could be, but probably not, because of two factors:
                1- When you calculate the needed take-off thrust for a given runway length, the required take-off thrust goes down as the runway length goes up, but only up to a point. After that, you can keep increasing the runway length and the required take-off thrust doesn't go down anymore. That's because the required take-off thrust must be enough not only to achieve lift-off within the runway with a certain margin, but also to sustain the climb with a minimum climb gradient.
                2- The above calculation is done assuming that an engine will fail at V1 (well, if fact at Vef, but that's splitting hairs). Typically said engine will not fail, and typically that fact will save your miscalculated day.

                However, there are factors that can make your day worse. Examples:
                - A grossly mistaken aircraft take-off weight, as was the case with that A340.
                - An engine failure combined with one of these miscalculations.

                --- 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


                • Originally posted by Gabriel View Post
                  The...most useless things in aviation:
                  The runway behind.
                  Except when you're trying to land a Cub in a 60-knot headwind.
                  Be alert! America needs more lerts.

                  Eric Law

                  Comment


                  • Originally posted by elaw View Post
                    Except when you're trying to land a Cub in a 60-knot headwind.
                    There aren't regulations prohibting that?
                    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                    Comment


                    • So how do you approach this problem...

                      A weight miscalculation, a degraded thrust issue, a drag issue or a wind issue will all be revealed to a performance monitoring system.

                      An incorrect runway calculation...?

                      That's just basic pilot error that can't be easily overcome with technology. But perhaps ground controllers could be required to transmit clearance for takeoff with both the runway designation and the available runway length. i.e. "Delta 123, clear for departure 31R you have 7300' " Something like that.

                      An incorrect thrust setting...?

                      Ex: the crew has initially planned a full runway departure but are rerouted to an intersection departure. They are aware of the runway length but neglect to change the takeoff thrust setting. Here, even a readback of the runway length won't help matters. But...

                      If the systems required the runway length given by the controller to be keyed in upon takeoff clearance, and the system could cross-check this with the weight and thrust settings, that should do it. It would not accept a thrust setting below a safe margin. Add to this a performance monitoring capability using accelerometers and air data. The system would know what to expect and warn if there is a significant performance discrepency.

                      Unless the ground controller mistakes the available runway length...

                      Comment


                      • Originally posted by Evan View Post
                        So how do you approach this problem...

                        A weight miscalculation, a degraded thrust issue, a drag issue or a wind issue will all be revealed to a performance monitoring system.

                        An incorrect runway calculation...?

                        That's just basic pilot error that can't be easily overcome with technology. But perhaps ground controllers could be required to transmit clearance for takeoff with both the runway designation and the available runway length. i.e. "Delta 123, clear for departure 31R you have 7300' " Something like that.

                        An incorrect thrust setting...?

                        Ex: the crew has initially planned a full runway departure but are rerouted to an intersection departure. They are aware of the runway length but neglect to change the takeoff thrust setting. Here, even a readback of the runway length won't help matters. But...

                        If the systems required the runway length given by the controller to be keyed in upon takeoff clearance, and the system could cross-check this with the weight and thrust settings, that should do it. It would not accept a thrust setting below a safe margin. Add to this a performance monitoring capability using accelerometers and air data. The system would know what to expect and warn if there is a significant performance discrepency.

                        Unless the ground controller mistakes the available runway length...
                        It's simpler than that. You have to link the take-off performance monitoring system with a GPS and an airport database. All except the take-off performance monitoring system already exist in most airliners and bizjets. The things needed for the performance monitoring system (basically an accelerometer and a database with the expected performance for each thrust setting/weight) exist too.

                        If you want to include wind issues you must include the airspeed and wind data assumed for the take-off calculation.

                        All the required data and initial technology is there.

                        Then we need a bunch of lines of code, years of test and certification, and several millions of dollars.

                        --- 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


                        • Originally posted by Gabriel View Post
                          I...and several millions of dollars.
                          ...for the lobbyists.

                          I hesitate to create things that are too dependant on GPS. Call me old-fashioned but I think that network is vulnerable. A human redundancy is needed.

                          Comment


                          • Sorry for resurrecting this dead body, but here we go again ("again" meaning different things here) and we almost have real dead bodies.

                            It was "just" a cargo 777, so it would have not been a major crash anyway (by Evan's definition, a major crash must satisfy two conditions at the same time: real big airplane and loaded with hundreds of persons).

                            As I've said it many times in this thread, I'd say it's time already.

                            Incident: Air France B772 at Paris on May 22nd 2015, 100 tons missing in inserted takeoff weight

                            On Jun 2nd 2015 the French BEA reported in their weekly bulletin, that the crew used 243 tons of takeoff weight instead of 343 tons for computation of their takeoff performance, the resulting speeds were input into the flight management system. During rotation for takeoff the crew noticed the aircraft did not become airborne, firewalled the engines, established maximum pitch possible without tail strike, lifted off, climbed out to safety and continued to destination. The BEA rated the occurrence a serious incident and opened an investigation.
                            http://avherald.com/h?article=48726439&opt=0

                            Air France pilots failing again.
                            But kudos to them for saving the day after their initial mistake. Managing thrust and pitch to maximize performance (without stalling in the process).

                            --- 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


                            • During rotation for takeoff the crew noticed the aircraft did not become airborne
                              That right there is what separates the professionals from the amateurs.

                              Joking aside, two things come to mind from the above:
                              1) I think Orville and Wilbur would be mighty impressed that an aircraft weighing 100 tons more than the pilots thought would be able to become airborne with a simple change in piloting technique.

                              2) With all the whizbang computers on modern aircraft, I'd think it would be possible to detect well before rotation time that the a/c is not accelerating as fast as expected and provide a warning to the pilots in time to reject the takeoff. This isn't the first time a plane has had a hard time becoming airborne due either to overloading (/being loaded more than the takeoff calcs considered) or reduced engine output, or both. AF90 immediately comes to mind, but there have been others.
                              Be alert! America needs more lerts.

                              Eric Law

                              Comment


                              • Originally posted by Gabriel View Post

                                ...As I've said it many times in this thread, I'd say it's time already...
                                Two hurdles:

                                1. The Boeing Bobby contingent with Mark IV-236A gluteal accelerometers (the 236A models are indeed accurate) who have never needed such a system and see no need for such a system.

                                2. You need to guarantee that there is no chance of unintended consequences- there may be an occasional false abort and one of them might cause a mid air collision after the abort causes another landing plane to go around and conflict with a plane on an intersecting runway...

                                ...still- since pilots are already monitoring engines and V1- they could put a little box next to the airspeed tape that said TOA (take off acceleration) and would be green or red and beep and you simply confirm this at airspeed alive, at 80 kt cross check and as you approach V1...

                                Doesn't seem too insidious...
                                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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