Well, mandatory is a funny word when it comes to the FAA. After the
Swissair 111 crash in '98. flammable material used in the aircraft's structure was blamed for a fire resulting in the loss of control and crash of the aircraft.
The FAA mandated it all be changed to a better material over a loooong period of time. And if im not mistaken, there are still plenty of aircraft flying with the old flammable material on board.....
