Before a new type of airplane goes into service, every part of it is tested again and again. But there are two tests that are more important than all the others.
在一架新型飞机投入使用之前，它的每一个零件都要经过反复检测，不过有两项检测更为重要。

The first is called the "tank test". A modern airplane must fly very high in the sky. Air must be pumped into the plane so that the passengers can breathe. The metal structure of the plane has to be very strong for this reason. When the plane is filled with air, the air presses against the skin of the plane inside. The pressure on a small window is like a huge foot that is trying to get out. If a small part of the plane were to fail, the plane would explode in the sky. To test the structure of the plane, the plane is lowered into a huge tank or container of water. Then it is filled with air. The pressure inside the plane is greater than it ever will be when it is high up in the air. Finally, there is an explosion. This does not cause so much damage inside the water tank as it would anywhere else. Engineers can discover which part of the plane has broken. Then that part is made stronger.
第一个被称为“密闭性检测”。现代飞机必须在高空飞行，空气必须被泵入飞机，以供乘客呼吸。因为这个原因，飞机的金属结构必须非常坚固。当飞机充满空气时，空气会压在飞机内部的外壳上。小窗上的压力就像一只正试图出去的大脚。如果飞机上有个小零件有问题，飞机就会在空中爆炸。为了测试飞机的结构，飞机会被降到一个巨大的水箱或容器中，然后充满空气。飞机内部的压力比它在高空时更大，最后发生爆炸，这对水箱造成的损坏应该和其他地方一样。工程师可以发现飞机的哪一部分有问题，然后对其进行加固。

The most dangerous test happens when the new plane is going through test flights in the air. The test pilot must find out exactly what happens when the engines are all shut off at once.The plane begins to fall like a stone.It is the pilot's job to find out how he can get control of the plane again. These two tests are examples of how planes are made safe before they ever carry passengers.
最危险的测试发生在新飞机在空中进行试飞时。试飞员必须非常清楚一旦发动机全部关闭，接下来会发生什么。飞机开始像石头一样坠落，飞行员的任务是找出如何能再次控制飞机。这两项测试就是在飞机载客之前如何确保飞机安全的例子。