Any GPS readings after the initial event are likely to be unreliable, as I explained in an earlier post
http://www.pprune.org/rumours-news/5...ml#post9168602
Both GPS antennae are normally on the top of the fuselage, one over the cockpit and the other a little further back and most usable satellites are above the height of the aircraft. The antenae require direct line-of-sight with no obstruction. With the aircraft tumbling its very likely that that will not be the case for much of the time. This will cause a lot of random spikes as my earlier post explained.