Hey everyone, thought I'd give my 2p here.
I am a commercial pilot, flew for Europe's "favorite" low fares airline for a while before moving into the world of corporate aviation. I've no experience on the A320 but I've got a few thousand hours in Boeing 737's and Citation XLS's to back up my opinions.
Sadly there are a lot of "experts" out there, even sadder still news channels like to talk to them and from a pilots perspective, it's embarrassing what comes out of their mouths sometimes. If you want facts, please disregard ALL mainstream media, please check out this rather excellent website which is well known in the aviation industry for being the source for reliable details:
http://avherald.com/h?article=483a5651&opt=0
As for what happened, well I'm often reluctant to speculate because there isn't usually just one thing that goes wrong. Aviation is a system of backup on backup on backup, each layer with a multiple of holes, but the hope is through all backups the error can't slip through. It's nicknamed the Swiss cheese model, for obvious reasons.
However, there are some theories, the most plausible in my opinion being a pressurisation problem. These are relatively common (Though I've never had one and don't know anyone who has) but it is a very well practiced procedure: Oxygen masks on, establish cockpit communication, diagnose, descend. Depending on the nature of the depressurisation depends on how fast you go down. If it's a structural issue then you do not put any undue stress on the airframe, go down slow and steady. If it's an outflow valve stuck open (just one example of a non structural pressurisation fault), then it's cut power, set 10,000ft, airbrakes out and set speed to Vmo or Mmo (speed or mach maximum operating). The 737-800 that I flew for that certain Irish carrier would be about 320kts, the A320 I believe it's 350kts, you'll descend very quick, initially we're talking 4000fpm+, reducing to maybe 2000fpm by 10,000ft. This means that the 10 minutes to descend is well within the flight envelope.
We use 10,000ft, or Flight Level 100, because at that altitude the air is thick enough for us to be alert, unless you're a smoker then you can knock a few 1000 of that figure.
Airbus aircraft also have protection from over stressing the aircraft, if it sees the aircraft over speeding it will reduce rate of descent and automatically retard the thrust levers. The speed of impact would likely have been at the top end of this, 350kts = 402mph airspeed, which at 6000ft could be 450mph ground speed depending on pressure/temp/wind. Whatever happens, nothing will be left of the aircraft, which backs up the photos that are surfacing now.
They were heading over towards the Alps, over the mountains you've got to be very aware of your sector safe altitude, the lowest you can descend in the case of an emergency, as the ground comes up to meet you. The area around Mt. Blanc for example, you cannot descend below 18,000ft, so you can imagine if there is a problem the pilots would not continue towards the mountains.
So, again IMO, this leads us to possible pilot incapacitation, did they get the oxygen masks on in time? Did they start the descent then put them on? If this is the case they'd happily be descending at the average 3400fpm descent totally unconscious. As they pass 10,000ft they'd slowly gain consciousness, pulling out of the dive at 6400ft, where they apparently flew level at this altitude for 1 minute before impacting mountains roughly 9,000ft in height.
The only flaws in this I can see are a) why did both of the crew not get oxygen on in time, it's the very first thing to do and b) why did they set level off altitude at FL064 not FL100 or even better, the MSA? Why carry on into high ground and not turn off route into flatter land into France?
There are reports of possibly no mayday call too. The squawk was not set 7700, again this strikes me as incapacitation. The old aviation saying; aviate, navigate, communicate, is important in this. Communication is last on the list of things to do. First is fly the thing, then fly not in the right direction, then finally tell people what you're doing.
It's strange, we wont know until cockpit and black box recordings are analysed, which I believe is already underway, so we'll know a bit more in 48hrs.
As for the age of the aircraft, 24 years is not old at all. Aircraft are maintained to a standard that would far surpass what anyone could imagine, I believe this one had a major check in 2013 and came out of maintenance just the day before. It made it's way to Barcelona too, so it was likely maintained correctly.
It's a very sad day for aviation, a very sad day to see my fellow aviators die too. But this is not a common thing, this is not normal and not something to worry about. The A320 is one of the most common and safe aircraft ever produced, I'd have all the confidence to fly one and fly in one.
Remember that there are 10,000+ flights per day, every day, so whilst there are accidents, these things are rare.
