On March 21, 2022, the crash of China Eastern Airlines touched the hearts of countless Chinese people, and the process of finding the black box of the crashed plane became the focus of the news.
What exactly is a black box? Generally speaking, a black box refers to a machine that does not understand its working principle. In electronic technology, instruments that only pay attention to their input and output signals without paying attention to their internal conditions are collectively referred to as black boxes. There are many things that can be called a black box in real life. For example, a computer is an out-and-out black box, because most people do not understand what the inner workings of a computer are.
For aircraft, black box (English black box) is the common name of aviation flight recorder. After an air crash, the plane is often disintegrated or even destroyed by fire. In the field rescue, the search for the black box known as the “witness of the air crash” is an important part. The black box can provide investigators with evidence to help them understand the truth of the accident and is the key to deciphering the cause of the accident.
Most of the black boxes installed on passenger and military aircraft are a complete system, including two different types.
One is a black box called an aircraft data recorder (FDR), which records various data in flight, such as flight time, speed, altitude, deflection of the aircraft rudder, rate of climb, rate of descent, acceleration, There are more than 30 kinds of data such as fuel consumption, engine speed, and temperature, which can be recorded for 25 hours. Before takeoff, as long as the switch of the black box is turned on, the above-mentioned data during the flight will be recorded in the black box. In the event of an air accident, these flight parameters can be re-extracted through special equipment for flight experiments and accident analysis.
The other is a black box called a pilot voice recorder (CVR), which can record various sounds in the cockpit with the help of speakers placed in the cockpit and the cockpit, including conversations between crew members, land and air calls and various background sounds in the cockpit, such as engine sounds, etc. Its recording time is 30 minutes, and the recording will restart after 30 minutes, so the black box records the important information in the plane 30 minutes before the crash.
The black box is a cuboid sealed metal container, about 40 cm long, 20 cm high and wide, not like a box, but more like a small streamlined container, each weighing 20 kg to 30 kg, and the interior is actually a transceiver letter machine. During the flight of the plane, the black box can receive various information collected in time, and automatically convert it into corresponding digital signals for continuous recording; when the plane crashes, the emergency positioning transmitter of the black box can automatically transmit specific frequencies in all directions. , “declare” its position. It’s a regular heartbeat-like radio signal that searchers can trace back and forth.
All the electronic instruments in the early aircraft were placed in a black square box of uniform size and shape, as was the flight recorder, and the storage box was more sturdy, so the early name “black box” lived up to its name. Today’s black boxes are not black, but are generally painted a bright orange-red. The striking color, along with the reflective strips on the outside of the recorder, helps searchers find the recorder quickly.
In order to withstand the violent impact and high temperature flames when the plane crashes, the black box is usually made of iron and some high-performance heat-resistant materials. Resistance to shock and vibration, resistance to seawater immersion, and resistance to magnetic interference. The recording medium has also been improved from a tape type to a static storage recorder that can withstand greater shocks. Similar to the memory chip in a computer, it can prevent the black box from being damaged in an air crash. damage.
For safety reasons, the two black boxes are usually installed in the safest part of the tail of the aircraft, that is, the part that is least damaged in the event of a crash, such as the rear passenger cabin, rear galley, aircraft tail compartment, rear cargo compartment sidewall, and rear crew rest compartment. side walls, etc.
After the plane crashed, the black box can withstand 30 minutes of grilling in a flame of 1100 ° C, can withstand 2.25 tons of objects being squeezed for 5 minutes, and can be immersed in gasoline, engine oil, alcohol, battery acid, and sea water for several months. All in all, it survives many harsh conditions.
Most of the causes of air crashes in the world are found through black boxes. For example, the black box on the Boeing 777 is equipped with an underwater beacon. When the black box encounters water, the underwater beacon is activated and sends out a 37.5kHz underwater acoustic pulse signal every second. 14,000 feet (4.27 kilometers) of underwater sound transmission for 30 days. Such pulses can be detected by sonar and acoustic locators. The black box is the only component that may send out signals after the passenger plane sinks to the bottom of the sea. If the black box can be located by means of underwater acoustic signals, the search range for the wreckage of the passenger plane can be narrowed, and the search for the black box is still very important.
In 1908, the first military aircraft accident occurred in the United States. In the future, with the increase of flight accidents, there is an urgent need for an instrument to study the causes of accidents. During World War II, flight recorders were officially used on military aircraft, and after the war they were further used on civil aircraft. The early recording methods were relatively backward, using mechanical recording methods and recording on photographic paper. After the invention of advanced magnetic recording methods, it became convenient and reliable.
Black boxes are constantly being updated. The black box that came out in the 1960s can only record 5 parameters, and the error is large. In the 1970s, digital recording tapes were used, which could record more than 100 parameters and save the last 25 hours of flight data. After the 1990s, integrated circuit memory appeared. Like the memory stick of a computer, it can record 2 hours of CVR sound and 25 hours of FDR flight data, which greatly improves the accuracy of air disaster analysis.
Although the black box is powerful, it also has many disadvantages. For example, even if it has a striking orange-red color, it is still not easy to find, because it can fall 20 meters underground when it falls from a high altitude. If it falls into the deep sea, it is a veritable needle in a haystack; sometimes, the black box is found. However, due to serious damage, it loses its use value; the beacon transmitter itself is easy to fall off, so the signal has errors and cannot be accurately positioned.
Many people ask, since the black box is so important and difficult to find, why is there no satellite synchronization backup for its information?
In fact, the current civil aviation system has been able to monitor the speed, altitude and other data of the aircraft in real time, and the aircraft itself can communicate with the ground in real time through satellite phones. However, if all kinds of flight data, cockpit dialogues and other information are really synchronized in real time , the amount of data is too large, and the cost is also high. Another reason is that, whether it is Wi-Fi on the plane, or the satellite phone, radar and other systems, there is no way to ensure the stability of the network signal, and it is technically impossible to store all key data synchronously.
It can be seen that looking for a mature and affordable flight parameter recording system is the future development direction. With the rapid development of modern electronic technology, this day may not be far away.
