Old 3rd Feb 2019, 07:37
  #980 (permalink)  
ATC Watcher
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Join Date: May 1997
Location: Europe
Age: 69
Posts: 2,609
Originally Posted by 42go View Post
May I gently inquire whether it is known if the loss of 'radar contact' was loss of primary or secondary?
Ok. let me play the armchair incident investigator , the report of loss of radar contact at 2300ft was made by Jersey ATC. the unit controlling the aircraft at the time . , they have apparently secondary only and I do not know at which altitude their filters are set at .
There at least 10 other radars covering the area including bot French and the UK air defense primary radar, and also a few local Air Force and Aeronavale /Navy lairbases in the aerea . In the hours / max a day that followed , an investigation of the recordings normally takes place to see if : 1 ) you can identify the aircraft , and 2) where the returns ended

Now to reply to DaveReidUK question :
Though I'm still not sure how knowing only altitude from basic Mode S can help with determining location.
With a mode S return you can very accurately calculate the ground speed and the final rate of decent and also see if the rate is steady or increasing etc.., with that you then have an angle and can determine approximately the point of impact if the aircraft continued on the same track of course .But my experience is that in this scenario , you normally do not see much deviation anymore the last 1000 ft . therefore you should be on the spot within 1 or 2 square miles . I noticed the BEA said it will be concentrating the research within 4 square miles, so here you go .
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