Here are a few ideas I posted in another thread... I don't believe there is a coverup, but the following is why I think that the last thing the goverment wants is for this to be an act of terrorism:
It's certainly understandable that the govt. and the airlines don't want to jump to the conclusion that this was a terrorist act. First of all, there's no evidence yet that points that way, and it would be irresponsible to say it was likely a terrorist act if the facts don't support that. Secondly, it would be a tremendous embarrassment and PR disaster for the govt. and the airlines if it were to be ruled an act of terrorism -- they would have a lot to answer for if such a thing could happen after the supposed improvements in security. Third, the economic impact on the airlines would be horrendous if people lose faith (any more than they already have) in the ability of the airlines to secure the aircraft against acts of terrorism.