One of the ways to improve flight safety was the use of on-board recording devices (BUR) for recording and subsequent analysis of the state of the main systems of aircraft. An emergency BUR is called a "black box", which is maximally protected from shock and thermal overloads, from the effects of aggressive media, etc.
Usually, two black boxes are installed on board the aircraft, one of which (speech) records the crew's conversations, the second (parametric) - flight parameters. This can be information about the operation of the engines, about the actions of the crew, about the meteorological situation, etc. In magnetic DRUs, data is written to magnetic tape or magnetic wire, in solid-state ones - to FLASH drives.
Outwardly, a "black box" and not black, and not a box - it is an orange sphere, inside which there is a recording equipment. The spherical shape for the BUR was chosen because it withstands physical activity better, and the orange color is more noticeable when searching. A protected on-board storage device (ZBN), as it is also called, must withstand a shock overload of 1000 g, heating up to 1000 C for 50 minutes and being at a depth of 6000 m for a month.
To facilitate the search, radio beacons are built into the "black boxes", which are automatically turned on after an accident. The drills are placed in the tail section, since in an accident it is usually less destroyed.
Recordings from magnetic tape or solid state drive are decrypted on the computer. Based on the data obtained, it is possible to simulate the behavior of an aircraft on a simulator or on a computer. You can also present this data in the form of regular graphs.
Despite all protective measures, flight recorders are often damaged in a crash. Decryption specialists have to recover information. For example, a dropwise colloidal suspension of ferromagnetic powder is applied to a magnetic tape. Powder sags under the influence of electromagnetic pulses. The result is a graphical image of the damaged magnetic recording.
Information is also recovered by the method of magneto-optical visualization. In polarized light, a picture of the tape recording becomes visible. However, both of these methods are applicable in cases where the film retains residual magnetization.