The preliminary speculation by the major news networks aviation experts frequently postulated the possibility of a pressurization problem aboard Germanwings flight 9535. The nature of the ill-fated flight belied this premise. A controlled steady rate of descent is not compatible with the standard high altitude jet procedure of an emergency descent at a very rapid rate of descent. Secondly, an additional procedure involves turning away from the airway to avoid other airplanes at a lower altitude. Also, the SOP for emergency descents is to level the aircraft at 10,000 feet above sea level (MSL). Neither of these items was accomplished. That is telltale evidence that the controlled descent was initiated and continued by a pilot at the controls as opposed to a response from an emergency. Also, there was no call to Air Traffic Control advising of an aircraft malfunction.
A NY Times report http://nyti.ms/19mdajf indicated that information from the CVR (cockpit voice recorder) indicated that one of the pilots left the flight deck and was unable to get back in the cockpit as the other pilot would not open the door. Was the other pilot incapacitated, or did he intentionally keep his pilot colleague from returning to the flight deck? The fact that the aircraft flew into the mountains of the French Alps in clear weather is powerful circumstantial evidence leading to a conclusion that the pilot remaining in the cockpit intentionally sabotaged the aircraft. Apparently, according to the info from the CVR, the pilot that was locked out of the cockpit was loudly pounding on the door and shouting requests to open it. This information was the result of a leak from someone who had access to the CVR tapes and for political and PR purposes has not been officially released. Perhaps, certain authorities will try to prevent this information from being disseminated.
On October 31, 1999 Egypt Air Flight #990 splattered into the Atlantic Ocean when an emotionally distraught copilot commandeered the aircraft while the captain was locked out of the cockpit. After the 9/11 hijackings the cockpit doors were reinforced and equipped with a very sophisticated locking system that prevented potential hijackers from entering the cockpit. The door must be opened form the cockpit. The US air carriers than adopted a very prudent strategy emanating from the Egypt Air incident. It was mandated that a flight attendant enter the cockpit and remain in the cockpit when either pilot must leave the flight deck. It appears that Germanwings did not have such a procedure. When the totality of the investigation is complete it is near certain that it will reveal that the pilot remaining in the cockpit intentionally caused the crash.