It started off like any other flight — with a routine morning ascent over a calm Mediterranean Sea that gave no hint of the terror soon to engulf Germanwings Flight 4U9525.
Typical turned to tragedy when the Airbus A320 smashed into the French Alps — and what was initially billed as a horrific mishap took on an altogether different dimension when the plane's cockpit voice recorder revealed the high-speed crash was apparently no accident.
Marseille Prosecutor Brice Robin gave details of the recording during a news conference Thursday. Here's what we now know about the crash.
Flight 4U9525, a 24-year-old aircraft registered as D-AIPX, took off from Barcelona bound for Dusseldorf with an expected flight time of just under two hours. Despite a 30-minute taxi on the ground, it was expected to arrive on time.
First Officer Andreas Lubitz and his captain — who has not been named — were "friendly" and "spoke naturally" during "a very normal conversation," according to the cockpit voice recorder, Robin said.
Weather conditions were good and the plane climbed normally as the captain briefed Lubitz on the expected approach and landing for Dusseldorf. Lubitz sounded "laconic," Robin said. "There is no real exchange as such."
The aircraft gently leveled off at its cruising altitude of 38,000 feet, giving the captain a perfect opportunity to leave the flight deck — presumably to use the bathroom.
He is heard handing command of the aircraft to Lubitz, then what sounds like a seat is heard backing up and the flight deck door opens and closes. Then, Robins said, "the co-pilot is alone in the cockpit."
As the plane reached the French coast, passing over the port town of Toulon, Lubitz initiated an unapproved, straight-line descent. It was gentle at first but soon reached a rate of up to 4,000 feet per minute.
Lubitz appears to have left the autopilot engaged, turning a small dial on the center of the instrument panel to select a lower and lower altitude while leaving the direction unchanged.
"This button is a button that turns many times to descend," Robin said. "You need to deliberately turn it. The action is deliberate. It was a voluntary action."
Then the captain tried to get back into the flight deck, but as is often common practice the reinforced door was locked and protected by a double-lock system, a code entry keypad and a video camera. Normally a pilot would show their ID to an interphone camera and whoever is inside releases the door.
"We hear several calls from the pilot to access the cockpit," Robin said.
But Lubitz never responded, even when the captain physically knocked on the door.
If a pilot becomes incapacitated in the cockpit, a code entered on a keypad will release the lock after a pre-programmed delay — but not if the double lock has been selected from within. The double lock cannot be overridden from the passenger cabin.
That means "we are speaking of a deliberate action to refuse to open the door … for the commander," Robin said.
For the final eight minutes before the flight crashed into the Alps, Lubitz was silent — but his breathing could be heard until the moment of impact, Robin said.
Air traffic controllers in Marseille noticing the plane's rapid descent, well below its planned cruising height, and tried to contact Germanwings 4U9525. They got no response.
Controllers then sent an electronic "squawk" — code 6700 — to the plane, which gives pilots who have lost radio contact the chance to make an emergency landing without coming too close to other planes. Again, there was no response.
Controllers then asked other aircraft in the area to try to contact D-AIPX — none were successful.
As the plane continued to descend, an aural altitude warning sounded, Robin said. That would have alerted the rest of the crew that they were now dangerously close to the Alps.
The next sound on the cockpit voice recorder is of someone trying once more to forcefully open the flight deck door — banging — but apparently failing to succeed.
In the final moments before impact, the cries of passengers can be heard on the flight recorder, Robin said. Then came the impact.
At no point, Robin said repeatedly, was any "Mayday" call made.