Germanwings flight 4U9525 crash: Helpless air-traffic controllers watched plane's fatal dive

COLOGNE/WASHINGTON (Bloomberg) - Air-traffic controllers in southern France diverted aircraft out of the fatal path of a Germanwings plane as it lost altitude, trying unsuccessfully to establish contact with the Airbus 320 before it crashed with 150 people on board.

"From the moment the control saw it go down, they made calls, multiple times," Mr Roger Rousseau, national secretary for air-traffic controllers' union SNCTA, said in a phone interview.

Flight 9525 left Barcelona on its way to Dusseldorf around 9.35am, before crashing in rugged terrain in the French Alps more than an hour later. Germanwings said contact with the aircraft was lost at 10.53am, less than 10 minutes after it had reached cruising altitude.

French air traffic controllers in the region declared an emergency at 10.47am as they saw the plane descending rapidly, said Mr Eric Heraud, a spokesman for French civil aviation authority DGAC.

Staff at the air-traffic control centre of Aix-en-Provence failed to contact the pilots over an 8-minute period before the plane disappeared from their radar, according to Mr Rousseau. The centre typically would have about 20 controllers on duty, keeping tabs on aircraft, he said.

"There were planes below it," Mr Rousseau said. "When the controller saw the loss of altitude, he cleared the flight path, he asked aircraft to change course."

An unannounced altitude change is rare and would cause an air-traffic controller to immediately contact a pilot by radio to find out what's going on, Mr Rousseau said.

"The moment you see a change in altitude, you know there's a problem. A pilot never does that."

One of the flight recorders has been recovered, though there is no hope of finding survivors, according to the French government. The cause of the crash hasn't been determined yet.

When a plane disappears from the radar, "you know that it's inevitably an accident", Mr Rousseau said. "There's emotion, a shock."

The two controllers tracking the flight were immediately replaced after the accident, and a psychological help group was set up, he said.