What do you or GA mean when you say that the captain had a partial incapacitation?
Partial or subtle incapacitation is where a person's ability to perform a task is seriously degraded but they may not be obviously or totally incapacited (unconsious for example). This could be caused by stress, fatigue, illness, drugs, alcohol etc or a combination of the above.
Can anyone enlighten us on whether Garuda must be established within stabilised approach criteria by 500 feet?
Garuda, like every airline, has stabilised approach criteria. Why some pilots (in any airline, in any country) press on when the parameters are exceeded I don't really know for sure but it would be fair to say that all pilots have been faced with this situation at least once in their careers and usually more often than once. Perhaps there is a perception that if we continue then no one will know anything was wrong. They'll fudge it a bit and all will be well in the end. This is where QAR and a rigourous Flight Operations Quality Assurance Programme can help. The QAR will always detect an unstable approach that is not followed by a go around. In this case the crew can expect to be contacted for an explanation followed by counselling and/or remedial training. The message will soon get through.
In the case of GA200, assuming the report of high rate of descent close to the runway is accurate, as well as a 'too low flap' GPWS alert this would have been followed by a 'sink-rate sink-rate' and possibly even a 'whoop whoop pull-up' GPWS. You would think that self preservation on the part of the FO would have kicked in at this point?