You know the thing about conspiracies is that they often underestimate just how bad the real world actualy is.
So forget 9/11, current year American aviation is going through a severe crisis, Blancolirio posted about this recently covering the recent close calls.
So its not like its impossible to have multiple failures and a massive coverup, its just that these failures would have been happening for months before and probably after 9/11.
In the current situation though, its literally a miracle there was no major incident so far, ignoring the Boeing stuff obviously.
