Comment: They already did, almost ten years ago.
The Courier-Mail 
April 5, 2011
Airplanes could be taken over by remote control and forced to crash with the use of newly invented computer software, according to an expert cited by The Courier-Mail on Monday.
Cyber attacks are now viewed by industry specialists as the second-biggest risk to aviation behind natural disasters.
Airline representatives were warned of the threat at the Asia-Pacific Aviation Security Conference in Hong Kong last week.
Australian cyber-security expert Ty Miller, from Pure Hacking, told the conference whole fleets of planes could be affected.
“The stereotypical ‘Die Hard 2′ airport attack, where aircraft controls can be taken over, is no longer just a movie script. It’s an actual reality,” Miller said.