MrN: The SSR data disappeared from the screen as the Mode C read F145 in descent. The controller was looking right at it when it occurred. The primary only target then made a slight right turn toward the coast, then it disappeared. Not sure for how long the primary target was visible after the SSR data was lost.
Interesting. This may be how it played on screens in Christchurch, (or maybe your information is second-hand and slightly incomplete) but on the Ohakea screen, the aircraft continued on track for up to a minute after the SSR failure, then executed a sharp
left hand turn back towards PP. At this point the aircraft was asked to confirm "ops normal". There was no reply. The primary symbol coasted 4.5nm bearing 010 from PP. (Primary cover to approx 1500 feet in this area).
The crew had just acknowledged a descent clearance to 7000 feet and were about to check the ATIS at Palmy when the transponder died. There was no mention of any weather or any other abnormality.
The aircraft was tracking on Foxton without any deviation and the groundspeed appeared perfectly normal.
I think we'll have to wait and see what the investigators find. I certainly hope they recover enough to determine what occurred.