A Dark Day: What Caused Germanwings Tragedy?

At least 700 people are searching for answers at the site of Tuesday's deadly crash of Germanwings Airbus A320 in the French Alps. Investigators are also looking for clues from one of the black boxes they've already recovered. 

The crash killed all 150 people on board, including six crew members and two babies.  Also on board were 16 high school students and two teachers from German town of Haltern returning from an

exchange program.  Two Americans also died in the crash.

Right now, officials are calling it a horrific accident and say hijacking or terrorism is unlikely.
    
Lufthansa is the German company that owns the Germanwings Airbus A320 passenger jet.

"This is a tragic moment for Lufthansa and really a dark day in our history," Lufthansa Vice President Heike Birlenbach said.

The Germanwings plane took off from Barcelona just after 10 a.m. Tuesday morning on a two-hour flight to Düsseldorf.

Germanwings Flight 9525 had just reached cruising altitude of 38,000 feet when suddenly it started a steep descent -- without a call to air traffic control.

"Looking at the rate of descent, and the profile we're aware of, it appears to be an intentional maneuver. Why, we don't know," Former NTSB Director of Aviation Safety Tom Haueter said.

The Airbus A320 is a plane with a good safety record, with 6,000 in service today. The plane that crashed had just undergone a routine safety inspection Monday.
    
Investigators say possible causes of the crash could have been the following:

• A quick depressurization
• Lack of oxygen, meaning the pilots could have become incapacitated
• Or they could have been overcome by smoke in the cockpit, making it difficult to see or operate the plane.

A third possibility: pilots were trying to deal with a problem and following emergency protocol to lose altitude and work on the issue.

"Normally, you fly the airplane first, and possibly they're dealing with heavy smoke or fire in the airplane. It may be their priorities didn't get to communicating yet," Haueter said.

For now, the search for answers as to what happened on the Airbus A320 continues.
    
Officials expect this search and recovery mission to be long because the crash site in the French Alps is so vast and remote.