Perhaps Fitz did it?! (note if you are familiar with one of the many sub plots on the TV show Scandal, where as a Navy pilot in his youth before becoming President, he shot down an airliner for yet unknown reason)
Seriously though, if an Operation Remington (the op name in the TV show) occurred, its another "theory."
All in all, there are simply too many theories and possibilities. Until wreckage and/or intact plane is found, then most theories can be weeded out and we would be left with a competing few.