For GermanWings Flight 9525, the threat was inside the cockpit

"So in any case, it's a voluntary action. According to the elements we have, we are talking about a voluntary action. Refused the pilot to come into the cabin, to force the plane to descend. It's like landing whereas the plane was flying over mountains." -  Brice Robin, French prosecutor 

Yesterday, French prosecutor Brice Robin stepped onto the world stage to relate the unthinkable. The plane's co-pilot had been in control when Germanwings Flight 9525 slammed into the mountains. He'd barricaded himself inside the cockpit and rammed ahead at full speed... ignoring the screams of 150 passengers behind him, and the frantic pounding of his captain at the door.

• This video shows how a pilot might have been locked out of the cockpit of Germanwings 9525

Already an immense tragedy, this new revelation about what brought down Flight 9525 will reverberate for years with those whose job it is to be on guard against threats to airline safety... just as the events of 9/11 led to new steps to secure cockpits against threats from the outside.

For his thoughts on how new steps might be taken to guard against threats from inside the cockpit in future, we reached Chris Yates. He heads Yates Consulting, an air safety, security and counter-terrorism firm in London, U.K. 

This segment was produced by The Current's Gord Westmacott.