Here's a timeline of exactly what happened inside the Germanwings plane before it crashed

Investigators are piecing together what caused an Airbus A320 operated by Lufthansa's Germanwings low-cost airline to crash in the French alps Tuesday morning as it was flying from Barcelona to Düsseldorf. All 150 people on board were killed.

In the latest development, a French senior military official who has knowledge of a cockpit audio recording says that one of the pilots was locked out of the cockpit and can be heard banging on the door minutes before the plane went down in a remote section of southern France.

As investigators continue to pick over clues from the crash site and examine two recovered black boxes, here's a timeline of everything we know about the events on the day of the plane crash, Tuesday, March 24.

8:55 a.m. GMT: Germanwings Flight 4U9525 leaves Barcelona in Spain bound for Duesseldorf in Germany. The plane was scheduled to land around 90 minutes later. There were 144 passengers and six crew members on board.

9:30 a.m. - 9:31 a.m. GMT: Air traffic controllers are unable to make contact with the plane during these two minutes. A top government minister said on Tuesday that what happened during this time is key to the investigation.

9:45 a.m. GMT: The plane reaches its highest cruising altitude of 38,000 feet. Minutes later, the plane begins to descend rapidly without explanation.

9:47 a.m. GMT: An air traffic controller issues a "distress phase" due to the loss of radio contact and because the plane was losing altitude so quickly. Contrary to earlier reports, the plane itself did not issue a distress call, a spokesman for DGAC aviation authority said.

9:53 a.m. GMT: Contact between the airplane and French radar and French flight controllers is lost at an altitude of about 6,000 feet.

9:53 a.m. - 10 a.m GMT: An official familiar with audio recordings from the German flight told the New York Times that one of the pilots was locked out of the cockpit in the minutes before the plane crashed. He can be heard knocking on the door and then trying to smash it down.

10 a.m. GMT: The plane crashes just before 10 a.m. GMT. In a news conference, the managing director of Germanwings says the plane crashed after dropping from an altitude of 36,000 feet to an altitude of 5,000 feet over a span of 8 minutes.

10:40 a.m. GMT: There are initial media reports of a plane crash in the French Alps.

11: 55 a.m. GMT: Investigators describe the horrific scene of the crash. "We saw an aircraft that had literally been ripped apart, the bodies are in a state of destruction, there is not one intact piece of wing or fuselage," Bruce Robin, prosecutor for the city of Marseille, told Reuters. French police confirm that no one survived. Later, the French Interior Minister says a black box from the crashed Germanwings plane has been found.

Currently, experts continue to examine the black box recorder found at the scene of the crash.

One of the pilots of the plane had 10 years of experience of flying for Lufthansa, German officials said at a press conference on Tuesday. Officials said the plane had been last checked by technicians on Monday and weather conditions were reportedly good at the time of the crash.