For the 40 plus years I flew, I flew behind airborne radars for maybe 30 of those years..
I never heard of a civilian radar that could see anything other than weather, primarily because its beam is a very narrow “pencil” beam.
It mus be narrow so that the exact size and location of large storms can be seen in a manner that allows circumnavigation. A wide beam sufficient to see aircraft would paint the ground and make two cells look as though they are one, thus making it impossible to plot a course between them.
Obviously fighters have a means of intercepting aircraft, but airlines are not designed for that purpose.
Intimate knowledge of airline schedules, the TCAS and carefully monitoring center frequencies during the planning period would have been his best means.
Thanks for the information. The last radar I worked on was a shipboard one and it was switchable for different conditions depending on the surroundings. One setting was good for weather while out on the ‘bounty blue’ a different one was good for inshore navigation but filtered out Weather returns etc. I just assumed that the commercial ones would be somewhat similar despite having a side to side sweep versus a rotating sweep.
That assumption thing can really ‘bite’ you ya’know?
I did get an introductory course on the radar for the helicopters we occasionally carried and they had some very impressive capabilities. But being military that’s to be expected.