I think too much is being read into the fact that this was the Line Training Captain's first trip as such.
WillFly380 has questioned the wisdom of pairing a new LTC with a trainee Captain. A new LTC has to start somewhere, and a trip, not with a trainee Captain, but an experienced Captain converting to type seems as good a starting point as any. He could have had a 250hr cadet on his plate, although that may have focused his attention somewhat more. No, the answer to this quandry does not lie in the training office.
Line training issues aside, the ability of near on 25,000hrs of combined flight time crew to not notice the bleed off of 30 knots below Vref is somewhat alarming no matter what the type of approach.
The fact that the approach was not thrown away at 500 feet for not being stable is of concern. 'Hundred Percent Please', #1398, tells us
"So for the PF, it may have been easy to revert to 320 operating mode. His levers haven't moved (as expected), he has regained the profile at 500 thus avoiding a G/A due unstable and now he just has to guide the A/C to the touchdown markings."
Regaining profile at 500 with thrust at idle is not avoiding G/A as unstable. From the information released, at 500', the speed was 134kts cf a Vref of 137kts and with a downward trend so the approach was unstable on a least 2 counts. A big chance a avoiding what was to follow missed.
The auto-throttle response or lack of it, should I say, is another point of interest. Surely at 500' when they "regained the profile", an inside scan would have revealed a downward trending speed and no AT wake-up. Surely time to "push 'em up"? But no, the aircraft fell off the profile and into three reds on the PAPIs and then four reds before the crew woke up to their plight, by which time the stable door was wide open and the horse was a cloud of dust on the horizon. This on a visual approach where eyes should have been on the runway and therefore the PAPIs.
I believe the CVR will provide shed more light on this accident than the FDR.