Only the examination of the black boxes and the cockpit voice recorder, once recovered, will give, perhaps, an explanation of some of the causes that led to the fall of the Germanwings A320 on the French Alps. But there are at least three factors that are already evidence to the investigators.

Failure to alert. One of the mysteries is that the two pilots of the Germanwings flight 4U9525, that crashed today in the French Alps, have failed to launch the alarm. The rapid descent to a probable sudden depressurisation in the cabin of the plane (one of the hypotheses that can be taken into account) is part of one of those manoeuvres that airline pilots do more often during the hours of training, in the periodic and mandatory simulator.

The two German pilots would have fallen by 31 thousand feet in 8 minutes having basically three choices, more or less imposed by the circumstances: the first one to make the descent, for reasons that only the voice recorder will tell us; the second one to come down over the "sector limits" imposed by the overflight area; the third one to come down much less quickly than is normally the case. The standard procedure is to 7,000-8,000 feet per minute to about 320 knots. If the information so far is correct, the Germanwings Airbus 320 instead dropped to about 4,000 feet per minute, going from the 38,000 feet agreed with the French navigation controllers to 6,800 feet in 8 minutes. A lot of time.

The fault that left the aircraft on the ground yesterday. As reported by Spiegel Online, the unit was left all day in 'AOG-modus' ("aircraft on ground") yesterday, at the airport of Dusseldorf, because of technical problems.

The unit reported problems on the "nose landing door", the front door of the landing gear, confirmed Lufthansa to Spiegel Online: "this problem was completely resolved and the aircraft was ready by 10 am yesterday morning for regular service," said a spokesman for the airline. "One problem, however, completely overcome to the point that the aircraft was able, from 10 in the morning, to take back its regular service."

The breaking of a window. Again, it produces an explosive decompression that - if addressed properly by the crew - provides for the rapid descent of the aircraft and the emergency landing at the first airport available on the route.

The previous incident. The dynamics is similar: a sudden loss of altitude. But in the case of the flight from Barcelona to Dusseldorf that crashed this morning in the French Alps, the outcome was tragic. While last November 5, fortunately, a Lufthansa aircraft (company that owns Germanwings) managed to avoid the crash thanks to the preparation of the pilots.