there could be explosive decompression as a result of some structural failure of the aircraft. everything flies around that's not tied down. it physically feels like it's punched. it's a physical event. if that's happened we expect the aircraft to have defuated deviated left to right. this is indication of some software failure in which there was an uncommanded control descent or perhaps incapacitation of some type for some reason whether through criminal intent by a crew member or passenger or by some other means, mechanical event or cascading series of mechanical failures. richard is right.