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  • Has Schiphol sunk?

    Hi,

    Firstly to say that this is one of my favourite ever website finds! Top notch stuff and my two yound boys are thrilled with this site. Well done!

    I live about 20km SW of Schiphol airport, Amsterdam and I have noticed that many of the aircraft report that they are up to -25m altitude when they have landed. Now I admit, Schiphol is a very low altitude airport at 3 metres below sea level. There is also a lot of variation, from around +40m down to -25m. I thought that this might be related to the local air pressure, but then I have also noticed that some planes land perfectly on the runway and other appear to land several 10s of metres to either side.

    What causes these innacuracies? Surely the aircraft instruments are pretty damn accurate, otherwise we'd have a lot more crashes on our hands. Where exactly does the transponder get it's data from? I assume that it must transmit the same data that the flight crew see in the cockpit.

    On a separate note, I assume that the strangely quiet skies over France and Spain tonight are due to volcanic ash once more. Really weird to see!

  • #2
    The reason why one often sees a negative value for an airport height is, I think, due to variations in atmospheric pressure around the globe.

    The pilot will request this value (from the control tower?) for a particular area before setting off on his flight from,say, Jamaica. The pressure at sea level off the coast of Holland is not going to be exactly the same as that off the coast of Jamaica - hence (I think) the negative value displayed on landing.

    There is a good explanation of "altitude in aviation" on Wikipedia (under the word 'altitude'). In addition, Wikipedia has many other useful pages eg. navigation, radar,flight planning, flight instruments, etc.

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    • #3
      If you check out Wikipedia under "flight planning", it mentions that Amsterdam Schipol airport is indeed below sea level (at -3 metres). How about that!

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      • #4
        If global warming really causes a rise in sea level, they will be able soon to convert their terminal facillities into a ferry port so people can sail across the North Sea. or they could run flying boat services.

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        • #5
          Thanks all for your comments! Schiphol had better remain dry otherwise I'll be swimming to work instead of cycling (I live 2m below sea level!).

          I also thought about atmospheric pressure and am already familiar with the principles of flight altitude (thanks ferret). If I get time I'll try and correlate the deviation in landing altitude with local air pressure. However, this doesn't explain why a plane can be shown to land parallel to a runway but be up to 1km into the fields... We haven't had many planes land in the fields here recently, except the Turkish 747-800 last year!

          I live directly under one of the main flight paths into Schiphol and I also notice that a plane can be plotted to be directly over my house at say 3000 feet and when you look up its actual position is significantly different (left or right I mean). At such low altitudes a kilometre left or right is easy to see.

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          • #6
            The height is quite often wrong at many airports on landing. I think that in most cases the reason behind is wrong QNH setting.

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            • #7
              The ModeS Transponder is set to standard atmospheric pressure = 1013 hPa
              If the local QNH is higher then the shown altitude is lower and vice versa

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              • #8
                Anyone using a Flight Simulator (my favourite one is MS FS2004) Will know that when Landing ILS.,
                the receiving airport ..alway gives his (airport) present QNH., Ive also noticed that over local airfield
                EDLM also give that info for incoming aircrafts.
                Which means.,It gives the aircraft/Pilot) the actual height that he /she will be landing..,
                Sorry.., I havnt got a PPL., (my brother did have one tho)
                (F-EDLE1)delcomp-DEL-David Tks(My friend Mike, all three of them)

                URL: http://banner.flightdiary.net/EDLM
                1090SJ(Ae) /(6m. Ecoflex10) / SBS 3 /-FR24 Box/ Power-line Connection (Ethernet)

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                • #9
                  Sorry again..., QNH., in pilot laugage is usually Altimeter.
                  (F-EDLE1)delcomp-DEL-David Tks(My friend Mike, all three of them)

                  URL: http://banner.flightdiary.net/EDLM
                  1090SJ(Ae) /(6m. Ecoflex10) / SBS 3 /-FR24 Box/ Power-line Connection (Ethernet)

                  Comment


                  • #10
                    Originally posted by simplastic View Post

                    On a separate note, I assume that the strangely quiet skies over France and Spain tonight are due to volcanic ash once more. Really weird to see!
                    This is due to there being very few (almost none) ADS-B receivers in France or Spain which are relaying data to FR24.

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