On March 21,2022,a China Eastern Airlines MU 5735 with 132 people aboard crashed（撞毁） in Guangxi. It dropped from 8,869 meters to l,333.5 meters in just three minutes. After days of searching, its two black boxes were finally found. That brought the hope of understanding what caused the country's worst airline disaster in years.
However, what are black boxes? A black box is also known as the flight recorder. Every plane has at least two black boxes. Usually, one is in the front and the other is in the back. They record everything about a flight such as its speed, altitude（高度）, conversations, and air pressure among other things. The information helps to discover what lead to an accident and prevent similar accidents in the future. Therefore, black boxes are usually installed on each plane.
The use of black boxes dates back to the early 1950s. It's said an Australian scientist named Dr. David Warren made the invention. He realized that people who can best explain what happened are unluckily dead. Then the idea of a voice recorder to be present in flights was born.
Although it is called black box, it is neither black in color, nor looks like a box. It is painted in bright orange color. So the people looking for it can have the best chance to find it. It is not certain how it got its name.
Each box weighs about 4.5kg. They are generally made out of special materials. This helps them survive（生存） from heat, cold or wetness. To make black boxes easier to discover under water, they can let out signals（信号） for 30 days.
