WAG - High on profile, Open Descent or selected V/S, APPR inadvertently armed instead of LOC (setting mental expectation of G/S capture), no glidepath to capture so aircraft continued in descent until 1sec(?) before impact when A/P is disengaged.
I've seen it happen several times in the past 13 years on the A320. Capture from above with no floor on the descent. Easy to fix if you catch it in time.
Last edited by AKAAB; 18th Aug 2013 at 22:12.