The so-called black box is the general name of the flight recording device and the sound recording device in the operation room. It can help people investigate the real situation at the time of the plane crash. There are generally two “black boxes”. One is the “data box” flight recording device. Once the aircraft takes off, it will automatically record the accurate data of the aircraft’s altitude, speed, direction and so on; The other is the “sound box” – cab sound recording device, which can not only record the conversation of drivers in the cab and their contact with the ground, but also record the suspicious sounds of various machinery in the cab. The black box is square and made of special alloy, which can withstand 1100 DEG; C high temperature for half an hour, can withstand the violent impact of aircraft explosion, and is not afraid of long-term immersion in seawater. Within 30 days after the plane crash, the black box can automatically and continuously send an electronic signal, an “acoustic pulse”, which can be controlled and measured even 6000 meters away from the seabed, which provides clues for rescuers to find the wreckage of the plane.