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Touchdown zone and landing distance calculations

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    Touchdown zone and landing distance calculations

    Dear all

    Sorry if silly question or has been answered previously on another thread - I had a look and cannot find anything that precisely answers my question.

    Suppose I am landing on runway X and use a landing performance calculator to determine that my landing distance at given Vref and autobrake setting will be 2000m. For the purposes of landing distance available, where on the runway does that start? Does landing distance needed start at, for example, the aiming point, or does it start from the very last touchdown zone marker?

    In other words, if I plonk the main gear on the very last touchdown zone marker, will that still give me my enough room to decelerate to taxi speed without a runway overrun?

    Thanks

    Hugh Morton

    #2
    Originally posted by pessimaster View Post
    Dear all

    Sorry if silly question or has been answered previously on another thread - I had a look and cannot find anything that precisely answers my question.

    Suppose I am landing on runway X and use a landing performance calculator to determine that my landing distance at given Vref and autobrake setting will be 2000m. For the purposes of landing distance available, where on the runway does that start? Does landing distance needed start at, for example, the aiming point, or does it start from the very last touchdown zone marker?

    In other words, if I plonk the main gear on the very last touchdown zone marker, will that still give me my enough room to decelerate to taxi speed without a runway overrun?

    Thanks

    Hugh Morton
    If not mistaken,

    Landing Distance. The horizontal distance traversed by the aeroplane from a point on the approach path at a selected height above the landing surface to the point on the landing surface at which the aeroplane comes to a complete stop.

    This point is usually 50ft above threshold
    Landing.jpg
    Chris Makris (Olympic260)
    PMDG Technical Support
    http://www.pmdg.com

    Comment


      #3
      Following on from what Chris has said, if we include the 50ft height above the runway until the aircraft comes to a complete stop, you will find this is defined as the Actual Landing Distance. However, the Landing Distance Available which is used when calculating and certifying an aircraft type's performance is defined as the distance from the landing threshold to the end of the runway and it does not include any stopway.

      All of the theoretical landing performance requirements and other factors affecting it can be quite complicated and difficult to get one's head around in practice, so I won't bore you with the meaning of Required Landing Distance, Landing Performance Limited Weights, Runway Surface Definitions and even any Go-around Limitations can be a relevant factor in the event of an aborted approach or landing.

      From a pilot's perspective, it is important to always carry out a proper landing performance check prior to TOD using the landing data for the individual runway and taking into account all of the available data necessary to ensure a safe landing, including the airfield conditions, aircraft performance restrictions, braking requirements etc., etc. Then all you have to worry about is landing safely at the correct speed with the mainwheels on the ground 500 to 1,500 ft from the runway threshold, without floating and finally bringing it safely to a halt on the remaining runway.
      Michael Codd

      Comment


      • ProPilot85140
        ProPilot85140 commented
        Editing a comment
        Just wait until they include EMAS in the LDA 🙃🙃🙃

      #4
      Thanks both

      What do you think to my statement "if the main gear touches down on the very last touchdown zone marker, all will be well"?

      Just wondering when a pilot would consider a go around. Clearly, it will depend somewhat upon weather conditions on the day and the speed of the plane above the runway. If the pilot thinks the main gear will touch down after last TDZ marker, he/she would be well advised to go around. However, given good conditions, if he/she were confident in getting the main gear down exactly on the last set of TDZ markings, do you think that is reasonable?

      Hugh Morton

      Comment


        #5
        I love the username
        Jeannette Benoit

        Comment


          #6
          Originally posted by pessimaster View Post
          Thanks both

          What do you think to my statement "if the main gear touches down on the very last touchdown zone marker, all will be well"?

          Just wondering when a pilot would consider a go around. Clearly, it will depend somewhat upon weather conditions on the day and the speed of the plane above the runway. If the pilot thinks the main gear will touch down after last TDZ marker, he/she would be well advised to go around. However, given good conditions, if he/she were confident in getting the main gear down exactly on the last set of TDZ markings, do you think that is reasonable?

          Hugh Morton
          I do not believe this is reasonable, given that those touchdown markings every 500 ft in a few cases could be as close as 900 ft to the midpoint of the runway (FAA AC-150 Appendix A). A full touchdown marking scheme is 3,995 ft beginning at from the bottom edge of the threshold marking (piano keys) to the end of the final touchdown zone marking (shorter/narrow runways have modification to this). You aim for the touchdown zone marker or aim point that is usually 1,000 ft from the threshold, and if you have trouble executing the landing by the first or second touchdown zone mark (another 500 to 1,000 ft) then you need remedial training.

          An interesting deviation from this is at the large EAA annual fly-in at Oshkosh where there are three different touchdown markers on the runway and ATC, controlling from a flatbed trailer along side the runway instead of the control tower, is landing three aircraft at a time on one runway. If you know how to fly this is not hard.
          Dan Downs KCRP
          i7-10700K 32GB 3600MHz 2080Ti

          Comment


            #7
            Numbers derived depend on the manufacturer. I currently fly the Airbus A319/320 and Airbus landing performance numbers are predicated on a normal glide path, flare and touchdown within the touchdown zone, max manual braking or selected autobrake and max reverse thrust.

            Prior to the Airbus, I flew the 757 and 767. Boeing numbers were determined essentially by calculating a touchdown within the first 500 or 1000 feet of the runway (I can’t remember now how it specifically reads. It’s amazing how quickly one dumps information.) with immediate maximum braking and reverse thrust.

            Operationally, I think Airbus numbers are more realistic because we obviously don’t plop the plane down and stomp on the brakes. However, both sets of numbers are sort of a “what could we do” vs what usually ends up happening.

            For example, at my airline, we rarely use the autobrakes on either the Airbus or 756, though we tended to use them more often on the 756. I think I’ve only used autobrakes twice on the Airbus so far. So right there your numbers are going to be inaccurate. But the big thing is knowing what the plane can do and what we have available to us. For example, ACARS data shows a landing distance of 5000 feet but we have 16,000 feet available in Denver, we clearly have performance to spare and don’t need to be aggressive on the brakes. But if we have a contaminated runway in Chicago and the numbers say we need 6500 feet on a 7500 foot runway 27R, we’re going to plant it on, select reverse and let the autobrakes do their job.

            Hopefully that all makes sense and isn’t too confusing.
            Sean Wood

            Comment


            • ProPilot85140
              ProPilot85140 commented
              Editing a comment
              Man that last scenario at Ohare gives me the heebie jeebies

            • swood721
              swood721 commented
              Editing a comment
              Ha Just one I pulled out of thin air using an arbitrary number, but we did land on 27R today so that’s what made me think of it. Though it’s probably not too far off considering how terrible the last few weeks have been here, with more to come. Thankfully I’m off the rest of the week so I’ll be watching the show from home!

            #8
            On 737NG's new QRH/OPT set, it's 455m air distance from threshold to touchpoint, I think it's 305m for non-factored and old data set you find on PMDG manual/EFB though.
            The aircraft hardware is the same, Boeing did this number change few years ago with different assumption on how pilot would flare.
            On 787 and 737MAX's data set, it's dynamic based on 7 or 8 second of flare on VREF.


            Normally when you landing, you aim the 300m/1000' point and flare to land on around 450m/1500', if you flare too far, generally over 3000' or 1/3 of the runway, go-around.
            ZHU Hai
            B737 Ground instructor

            Comment


              #9
              Originally posted by pessimaster View Post
              Thanks both
              What do you think to my statement "if the main gear touches down on the very last touchdown zone marker, all will be well"?

              Just wondering when a pilot would consider a go around. Clearly, it will depend somewhat upon weather conditions on the day and the speed of the plane above the runway. If the pilot thinks the main gear will touch down after last TDZ marker, he/she would be well advised to go around. However, given good conditions, if he/she were confident in getting the main gear down exactly on the last set of TDZ markings, do you think that is reasonable?

              Hugh Morton
              Not a lot, Hugh!
              Seriously though, all will be well only when you turn off the runway at a safe taxying speed, arrive safely at the Gate and complete the shutdown checks. Until then you need to stay alert and don't assume anything. For example, it can still be easy to get caught out even after you have landed safely and in the correct place, only to find the aircraft subsequently starts to aquaplane or weathercock into wind just as you thought you had 'cracked it'.

              Most pilots are trained (or should be) to consider a go-around happening at any time during every approach and landing. Then, when they have to carry one out for real it won't come as a big surprise. This same principle also applies to the rejected takeoff case, because it is far better to have a pleasant surprise when they don't happen than to have a big shock when they do; especially if the flight crew haven't briefed and prepared themselves for one. Think of it as an essential part of Basic Airmanship and Planning Ahead! 😊
              Michael Codd

              Comment

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