You are the pilot on an airbus 320...you cede control of the plane to the co-pilot and get up to take a leak. However the co-pilot has quietly "come off the rails" and decides to commit murder/suicide by crashing the plane in a deliberate controlled 8 min decent into a French mountain. You come back from relieving yourself, can't re-enter the cockpit and realize the cockpit door has been intentionally disabled and the plane has gone into a decent.
You frantically call for the co-pilot to open the door while your ears are popping from the decent. The passengers see you getting more frantic and agitated and trying to break the door down with an axe and soon they realize it is bad....real bad....they start to scream, vomit, and pray.
After a minute or so you realize the co-pilot is nuts or incapacitated and you hit a panic button situated near the outside of the cockpit door that can only be operated with a passcode.
Cockpit control of the aircraft is disabled and is immediately transferred to a 24/7 on call pilot at Lufthansa headquarters that now flies the aircraft remotely (like a drone) to the nearest airport and lands safely.
That remote connection is secured by VirnetX. This type of fail-safe would work for a disabled pilot or a hijacking where the perpetrators gained control of the aircraft or for a rogue pilot that came off the rails and wants to commit mass murder/suicide.