A MD-80 pitched down during an autoland just prior to 50 FT. The pilot disconnected the autopilot and completed the landing and roll out.

Narrative

Aircraft was downgraded to CAT I due to over 60 days since FCC. Elected to attempt autoland FCC. Preflight autoland test was successfully accomplished at departure airport. The winds were light and variable with clear skies. The aircraft was on speed and stable down the entire glideslope until after passing 100 FT and just prior to 50 FT. Aircraft callouts were normal. Approaching 50 FT; the autopilot started to push the nose down in an aggressive manner that I did not like. I immediately turned off the autopilot and manually landed the airplane. The First Officer said he saw 'align' on the mode annunciator but did not see flare. I believe the reason is that the autopilot was off just prior to the 50 FT point. Needless to say; this is just about the worst scenario to occur; especially on clear weather day. I do not know what caused the strong nose down push nor what the outcome of the approach/landing would have been. My decision to land the airplane manually was obviously based on clear weather conditions and the 'visual approach' we were performing.