Severe updraft.
The computers would override pilot inputs, putting the a/c into a dive with increased speed. At over 32k’ there is plenty of time for a stall recovery.
follow-on articles:
headline: Pilots Disabled Critical Computers Moments Before AirAsia Crash
headline: French co-pilot flying AirAsia jet before crash-investigators
http://www.reuters.com/article/2015/01/29/us-indonesia-airplane-idUSKBN0L20BD20150129
now, the reuters article is a little funny, in that the headline is the Frenchy was flying, but down the article it says, “Captain Iriyanto, 53, an Indonesia air force veteran with about 20,000 flying hours logged, was believed to have taken over control of the aircraft from the less experienced Plesel when it started to ascend and then descend..”
So who was riding the plane down?