Jetstream67:
Secondary radar stopped abruptly (Flight24)
But Primary radar (where? Whose? What type) continues tracking long enough for searchers to issue a claim it 'turned back' (so 180degs exactly ?? and at what turn rate- a few clues from that maybe ??), Then vanished. (n.b. even small lumps of metal don't just vanish on (presumably) military radar which can also normally tell altitude from return range !!)
Military radar usually measures range and angles (and often closing speed too). However, at low angles, elevation angle measurements, and thus altitude measurements, can easily become unreliable because of multipath and possibly even ducting effects. At this point, the angle seems low enough that measurements may not have been accurate enough to usefully indicate altitude. Multipath effects can also cause the target to vanish.