01/02/2011

Extra work for Skyguide ATC in winter

With the ski season now upon us, there are many flights from the British Isles coming over Geneva to and from Chambéry. Sometimes these aircraft cross quite close to Geneva air traffic, giving the Skyguide Air Traffic Controllers some extra work.

Aer_Lingus.jpg


Just a week ago, around Christmas, a sharp-eyed user of the ARAG Geneva aircraft movenent enquiry system (GAME) noticed that some of the aircraft which were indicated were actually going to or from Chambéry (or perhaps Annecy) airport. When he contacted me I said that I had actually noticed this already and was working on a way to indicate for which flights this was the case.

From an examination of the data available, it is fairly clear that these are normally flights of companies operating between the British Isles (including Dublin, which is in Eire) and Chambéry. The website of the airport indicates that the airlines operating regularly to Chambéry in winter are British Airways, Flybe, Jet2.com and snowjet (who operate with aircraft of Titan Airways and also fly to Sion). However, it is quite likely that other airlines operate charters: we have detected such flights by Cimber Air, Globus and Thomsonfly, and there may well be others.

One quite interesting example of this happened this morning, 2 January 2011, when GAME detected a definite landing and a possible landing of two different Aer Lingus flights at virtually the same time. By consulting the plots of the trajectories it is easy to see that the first one (EI-DEG) corresponded to a flight from Dublin to Geneva, whilst the second one, G-ZAPZ marked as simply "Down", actually overflew Geneva towards Chambéry at a descending altitude that clearly indicated that it was about to land somewhere.

The trajectories plot is quite interesting in that it showed the two aircraft of Aer Lingus crossing within 30 seconds and at an altitude difference of about 1000 metres. The exact cross-over point shows the first one (for Geneva) at 8h48 and an altitude of about 1650 metres, then the second one (for Chambéry) 30 seconds later and an altitude of about 2500 metres. Add that to other Geneva arrivals beneath it, plus a departure over Versoix which did a U-turn to come back to the same area at a higher altitude, and you understand why Air Traffic Control is a skilled and demanding job.

Since the detected transmissions from these Chambéry-bound aircraft never include ones when the aircraft has landed, because Chambéry is too far away, the movements are indicated as either "Up" or "Down", and the explanatory in-line documentation says that these are not certain to be at the airport. A similar explanation applies to many helicopter flights, which may land anywhere. Indeed, when driving from Meyrin to Versoix via Ferney-Voltaire a couple of days ago I saw the yellow HUG helicopter landing in a field just close to the Customs post on the Ferney-Versoix road.

For modern aircraft for which the transponder broadcasts its global position, it is possible to detect this case of an aircraft landing or taking off far away from Geneva airport. The modification to the detection program is now under test, with an introduction planned in a few days time. It will also be possible to re-process the stored transponder data and detect and correct a posteriori all such non-Geneva movements since May 2008 and to correct all previous results. A provisional indication method might be to mark them as "up" or "down", rather than "Up" or "Down", but I am open to all other suggestions.

For other aircraft, including almost all private jets, which do not indicate their global position, it is very difficultg to be sure exactly where they landed. Thus, we always treat "Up" and "Down" indications for these with caution.

Let us hope that all of these skiers return home without a plaster cast on their leg.

 

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