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Black boxes help air crash investigations

  The black box is a product that has slowly developed in the continuous investigation of plane crashes since the advent of the plane, and it has concentrated the wisdom of many engineers and pilots. Its full name is “Flight Information Recording System”, which usually starts to record and store the flight data and voice information of the most recent period after the aircraft is started. The new data will continuously overwrite the original data, which can save and restore the entire flight data to the greatest extent for analyzing the cause of the accident.
  Early flight recorders were mainly used on military aircraft, and later on civil aircraft. In order to better discover the black box after an air accident, it is usually installed in a more eye-catching orange box (the surface is painted with a “flight recorder, do not open” prompt), and the surface is also affixed with a reflective light for easy searching at night logo. The black box is generally installed at the tail of the aircraft, because in the vast majority of air accidents, this part is often preserved relatively intact.
  Each airliner has two black boxes, a cockpit voice recorder and a flight data recorder. Among them, the cockpit voice recorder is also called “cockpit call recorder”. It is actually a radio call recorder. It starts recording when the aircraft is powered on, and stops when the power is turned off. The recording time is about 2 to 3 hours. It can record 4 channels of sound, namely captain channel, co-pilot channel, backup channel and ambient sound channel. The flight data recorder mainly records the altitude, speed, acceleration, heading, flight time, pitch angle, roll angle and vertical speed of the aircraft, as well as about 1000 flight parameters such as the operation of the crew such as the amount of the steering wheel and the throttle, and the recorded time The range was at least the last 25 hours before the plane was powered off, or the last 25 hours before the crash.
  The black box is one of the most sturdy parts on the plane, 50 cm long, 20 cm wide, 15 cm high, and weighs 20-30 kg. It has 4 layers, from the outside to the inside, it is made of corrosion-resistant titanium and stainless steel double-layer shell, high-temperature insulation layer, cold-proof insulation layer and storage, which can resist impact and extrusion, anti-magnetic interference, anti-corrosion, high temperature resistance And resistant to seawater immersion. The United Nations International Civil Aviation Organization has clear requirements for the material of the black box: it can withstand an acceleration of 3,400 grams, which is equivalent to 3,400 times the acceleration of gravity, which is approximately equivalent to an impact at a speed of 500 kilometers per hour; the fire resistance time at a high temperature of 1100 ° C can be long. Up to 60 minutes, the seawater immersion time is 30 days, and it can withstand the pressure of 6000 meters deep sea.
  In addition to providing the most powerful evidence for recreating the scene of the air crash, the black box also has other functions. For example, it can be used to monitor the daily driving of pilots and correct their bad driving habits. Because in the analysis of the causes of various air accidents, pilot errors account for about half of the accidents. For another example, the aircraft operating status and component health status can be monitored to eliminate potential accident hazards.

Black Box – a piece of equipment that must be installed on all passenger aircraft as stipulated by international civil aviation

  The replacement of black boxes is very frequent, which greatly improves the accuracy of air accident analysis. The first generation of black boxes was born in the early 1950s. It was improved on the basis of aircraft design and flight test recording equipment. Its working principle is to reflect the data change curve by leaving scratches on the metal foil tape with a needle, which can only record. 5 flight parameters including heading, altitude, airspeed, vertical load and time. The second-generation black box was born in the late 1950s. It is similar to an ordinary tape drive, but a protective casing with shock resistance and fire resistance is installed outside the tape drive. Generally, dozens of parameters can be recorded. Cockpit audio recorder. The third generation of black boxes appeared in the 1990s. With the rapid development of microelectronics technology, black boxes have begun to use semiconductor memory to record data, and the recorded parameters are generally hundreds. The functions have gradually extended from flight accident investigation to daily pilot monitoring, aircraft fault diagnosis and maintenance.
  The latest generation of black boxes can record video information with thousands of recorded parameters, and can regularly transmit key data through data links such as satellites. In addition, a new type of throw-away black box has also appeared, which can automatically separate from the body when the plane crashes. The National Transportation Safety Board also recommends installing a third black box on the plane. In addition to recording flight parameters and cockpit calls, a camera can also record real-time footage in the cockpit to better analyze the cause of the accident.
Difficulty in searching and decoding

  The importance of the black box need not be overstated. Hard-core protection measures can generally ensure the security of black box data. But after an air crash, the plane crashed in the ocean or on land, and finding the black box is very difficult.
  Finding the black box in the water mainly relies on two sets of positioning systems: “underwater positioning beacon” and “passive sonar beacon”. After the black box enters the water, its “underwater locator beacon” will automatically turn on and continuously transmit signals until the power of the black box is exhausted. Under normal circumstances, the power can ensure that the “underwater positioning beacon” works for one month. Therefore, it is best for rescuers to find it within 30 days, otherwise the black box will become a “needle” in the sea when the power is exhausted.
  The signal emitted by the “underwater positioning beacon” is divided into two frequencies: high frequency and low frequency. High-frequency “underwater positioning beacons” can emit sound waves with a frequency of 37,500 Hz, which are stronger and easier to detect. However, the range of the signal is limited, generally it can only be detected within a range of 4 kilometers, and it is more power-intensive, and it can only operate for 30 days. The low-frequency “underwater positioning beacon” uses 8800 Hz sound waves, which can be transmitted to areas 20 kilometers away on the sea and can be heard by the human ear. Because its frequency is relatively low, it saves power and can run for 90 days. And “passive sonar beacons” are specifically used underwater. Since the pure sound signal will be attenuated continuously in the underwater environment, the towed sonar can be used to measure the distance, and then continuously approach to complete the positioning.
  Even so, searching for black boxes at sea is extremely difficult. Compared with the vast sea surface, the search range of more than ten kilometers is too small, which will inevitably make it difficult to locate the black box. Even if the positioning is successful, deep-sea salvage still has problems such as difficulty, long time, high cost, and even inability to salvage. According to statistics, from 1970 to 2009, among the 36 accidents of large civil passenger planes crashing on the high seas, 4 of them have not found the wreckage of the plane, and 9 of them have not found the black box.
  Searching for black boxes on land is currently mainly using their bright appearance, unique color and reflective markings, relying on artificial vision and the nose of search and rescue dogs. If the black box is buried, rescuers can use ground-penetrating tools such as metal detectors to find it. In order to expand the search scope and avoid omissions, it takes a huge amount of manpower to carry out a carpet-like and drag-net-like search.

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