Sources: Malaysian PM via AP on YouTube, The Guardian, BBC News, Associate Press
quote: Phugoid oscillations for larger aircraft with improper trim are typically less than a minute to a few minutes. On United 232, it was about 40-60 seconds. That was a 55 meter DC-10, not much different from a 61 meter 777.It's highly unlikely that the reported altitude variations (~20,000 feet) could've been caused by a phugoid. At most you'd expect to see a variation of a few thousand feet.http://en.wikipedia.org/wiki/Phugoid
quote: The later course changes are harder to understand but it's possible that the plane was flying dead stick with the auto-pilot off. Small instabilities can cause heading changes before the fly by wire safety systems override and level the plane out again (doesn't happen until the plane is rolling 30 degrees or more to one side). Of course, it's also possible that the flight crew was suffering from hypoxia (either from smoke inhalation or decompression) and was simply not making good decisions by that point.