This Evening Standard article on the 3rd March said:

A hijack-proof piloting system for airliners is being developed to prevent terrorists repeating the 9/11 outrages.

The mechanism is designed to make it impossible to crash the aircraft into air or land targets - and enable the plane to be flown by remote control from the ground in the event of an emergency.

This got onto Slashdot.

Shortly after the events of 11th September 2001, the late Joe Vialls floated the idea that something of this kind might have actually been the mechanism used on that day. This idea never gained much credence, partly because of his poor general credibility.

But if remote control of airliners is a possibility, it's worth considering: there's a huge difference between the personalities of Mohammad Atta and his associates as exhibited in their behaviour in Florida and those of genuinely fanatical suicide operatives. Maybe they thought they were doing something quite different from what they actually were doing.

This was also discussed by George Washington's Blog:
http://georgewashington.blogspot.com/2006/01/wheres-remote-control.html.