To prevent collisions of aeroplanes with mountains, several major airlines have announced plans to install a satellite-based navigation system in the cockpits of planes. The equipment, called enhanced ground proximity warning system, uses the global positioning system of satellites to pinpoint the exact location of the plane. With this information, the system uses a huge database of the world's mountains to decide whether a collision is likely or not. If there is a chance of a collision, it warns the pilot about a minute in advance, as opposed to a few seconds with the currently used systems. The airlines plan to install this system in about 4,500 planes worldwide ( Communications of the ACM , Vol 41, No 2).