It's easy -- and perhaps tempting -- to try to draw parallels between the crash of the Germanwings Airline in the French Alps on Tuesday and previous tragedies like that of AirAsia Flight 8501, which crashed in December. After all, both incidents involved an Airbus A320. But as understandable as it is to try to draw lessons from earlier tragedies, it is also essential that we don't forget that no two accidents are ever exactly the same.
So what do we know about this specific incident? And what might have led to the obliteration of this plane, and the likely loss of all 150 people on board?
It's important to understand that airplanes don't just fall out of the sky for no apparent reason. And, quite frankly, airplanes don't just fall out of the sky even if a problem is experienced. As we witnessed from the U.S. Airways plane landing on the Hudson River in 2009, airliners can still fly without engine power.
So what may have happened here?
Understand that at this point, everything is purely speculative. From the response the world is witnessing, it appears that the accident investigation and recovery operation is proceeding at a professional level, appropriate to International Civil Aviation Organization standards. That's at least some positive news because we'll eventually have answers for the families of the victims.
Here's my take on what might have unfolded, based on what we have learned so far.
It appears from the data publicly available that the airplane began a controlled descent through the use of the autopilot, or through the hand-flying of the pilots. The descent was rapid, but not abnormally so.
It seems that an event occurred that compelled the crew to descend. But that raises the question of what that event could be?
An engine failure is one theory. Loss of engine power would not allow the airplane to maintain the cruise altitude it was originally assigned. It would have to drift down to a lower flight level. The airplane would also not be able to maintain its original airspeed. This is consistent with the data publicly available.
The crew would be following a checklist that would eventually end with a diversion to an alternate airport. As we know, the diversion didn't occur. It's possible the crew became preoccupied with the emergency, and with low ceilings and visibilities at the lower altitude, lost awareness of the mountainous terrain.
Another theory is that a smoke and fire event began at cruise altitude that required the crew to don their oxygen masks and goggles. The situation may have intensified to the point that the visibility in the cockpit was terribly restricted, making it not only difficult to execute a checklist, but difficult to fly the airplane at all. Even under ideal conditions, the use of oxygen masks and goggles makes it awkward to fly the airplane, communicate and execute a checklist. In smoky conditions, the difficulties are exacerbated.
If the crew became focused on the emergency and encountered worsening weather at lower altitudes, it may have become the perfect storm for loss of situational awareness with the terrain.
Another potential (although less likely) scenario is that a gradual loss of pressurization at high altitude may have created a hypoxia situation, rendering the crew unable to function normally. An explosive loss of pressurization is obvious, something airline crews train for frequently. But a slow loss of pressurization is sometimes difficult to recognize or detect initially. With the crew disabled, the airplane struck terrain.
But the truth is that at this point, anything is possible. The investigation process has to play itself out. The only thing that seems certain is that there was more than one factor that contributed to this tragedy.
Les Abend is a Boeing 777 captain for a major airline with 30 years of flying experience. He is also a CNN aviation analyst and senior contributor to Flying magazine. The opinions expressed in this commentary are solely those of the author.