Taken from this mornings Metro (7th June, London, UK):

A friendly greeting caused a major airport security alert when a man called Hi, Jack to a colleague on board an aircraft.

A SWAT team and dozens of police reinforcements were called to the Oakland International Airport near Detroit in the US.

Lt. Rick Crigger said, There was a guy on the plane named Jack, and someone walked in and said, Hi Jack. The mike just happened to be open and the tower heard it.

Thinking someone was hijacking the corporate jet, the FBI as well as police were called to prepare for a hostage situation. Air traffic controllers ordered the plane to return to the tower but, after a quick check on the identity of the pilot, the jet was cleared for take off.