According to recent reports, cockpit voice recordings of the jet, that crashed in the French Alps, have shown that one of the pilots exited the cockpit and could not get back in before the plane crashed.

The reason why the pilot left the cockpit is not clear. Investigators are studying the black box to get answers to some unanswered questions.

The recovery of one of two cockpit recordings came as, Germany's Angela Merkel, French President Francois Hollande and Spain's Mariano Rajoy visited the crash site to pay homage to the 150 victims.

France BEA air investigation Bureau director Remi Jouty said "We have just been able to extract a useable audio data file."

The BEA said the plane started plunging downward a minute after reaching height and then kept losing height for over nine minutes. The last words of the pilot were "thank you".

According to a senior military official who is a part of the investigation, the cockpit voice recordings showed "very smooth, very cool" talk between the pilots in the early part of the flight. The recording then suggested that one of the pilots left the cockpit.

The Lufthansa spokesman said that cockpit doors cannot be unlocked from the outside, since the September 11, 2001 twin tower tragedy.

Victims included Germans, Spaniards, three Americans, a Moroccan and citizens of Britain, Argentina, Australia, Belgium, Colombia, Denmark, Israel, Japan, Mexico, Iran and the Netherlands, reports revealed.

Germanwings, the budget arm of Lufthansa, said it had cancelled one flight on Wednesday. Some of its crew members had refused to fly, and it was using 11 planes from other carriers for about 40 flights.