airlines flight 370 sparking new calls to improve air security by making it impossible to shut off a jet's key safety system. suggestions include better protection of the voice and data recorders, making it practically impossible for anyone to cut power to these devices in mid-air, and possible expansion of real-time satellite tracking of practically all airliners. john, great to see you. let's break it down with the four systems that you did in your article. these are the systems that could be tampered with. start with the acars. what is it and how can it be tempered with? >> the acars system is likened to twitter for airplanes, occasionally sending periodic status updates from the airplane, that can even in some cases include the position of the aircraft. if a various system is changed on the airplane, if something