Such a disaster once almost happened.Two large planes were flying towards the airport.One was carrying 69 passengers from Toronto,the other 176 passengers from Chicago.An air traffic controller noticed on his rader screen that the two planes were too close to each other.He ordered one to turn to the right and to climb.But he made a mistake.He ordered the wrong plane to do this.So,instead of turning away from the second plane,the first plane turned towards it.Fifteen seconds later it flew directly in frout of the second plane.They avoided each other by the smallest part of a second.The distance between them was less than that of a large swimming pool.This is an example of the danger that grows every year.

曾经差点就发生了这样一场灾难。两架大型飞机都飞向同一个飞机场。一架飞机上有69名来自多伦多的乘客，而另一架上有176名来自芝加哥的乘客。一名空中交通控制员从他的雷达屏幕上观察到这两架飞机互相靠得太近。于是，他命令第一架飞机向右转并上升。但是他犯了一个错误。把这个命令发给了第二架飞机。因此，第一架飞机与第二架飞架靠近了而不是远离。15秒之后，第二架飞机直接飞到了第一架飞机前面。因为他们彼此差远远不足一秒钟的时间因而避免了相撞。他们之间的距离不足一个大的游泳池。这就是每年都在发生的危险之中的一例。