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Q&A about Flight MU5735 Crash and Safety Knowledge

  At about 14:38 on March 21, Beijing time, China Eastern Airlines flight MU5735 lost contact and crashed over Wuzhou City, Guangxi, China while performing the Kunming-Guangzhou mission. There were 123 passengers and 9 crew members on board. Rescue work is underway at the time of writing. In addition to praying for these compatriots and their families, we bring some Q&A about flight MU5735 crash.

  Q: From the existing cases, what are the causes of plane crashes?


  Aircraft are airborne objects, and a catastrophic failure can crash the plane, leaving the occupant with a very small chance of survival. An aircraft is generally composed of a body, an engine, and a control system. The mechanical structure of the airframe, flight control sensors, computers, rudder surface control systems, etc. may all fail. In addition, there are people operating the aircraft. Therefore, aircraft accidents are often caused by multiple aspects, including environmental factors.

  For example, a mechanical failure may cause the landing gear to be unable to be lowered or even the wing to break. Of course, such a thing as a broken wing rarely occurs, because the strength of the aircraft has been designed to be very good, and various overloads have been tested. Another example is the engine parking in the air, bird strikes, icing, oil circuit failure and so on. The failure of some sensors in the flight control system, such as the failure of the angle of attack sensor and the airspeed sensor, causes unexpected changes in the flight parameters and states obtained by the aircraft, which will bring problems to human operation or autopilot. It is also possible that the failure of the circuit and the oil circuit will cause the aircraft to not be able to operate normally. These are all problems of the aircraft itself.

  But it may also be caused by the external natural environment, such as icing, wind shear, the aircraft entering the icing layer, and the fuselage is covered with thick ice. If it is too late to melt, it may also lead to a crash. Wind shear can cause the aircraft to drop altitude instantly, or even lead to disintegration.

  Then there is the human error in operation, and there will be an accident. Therefore, there may be many reasons for the accident, which requires accident investigation and analysis to finally draw a conclusion.

  However, there is always an accident chain when an accident occurs, such as inspection, maintenance, operation, environment, etc. As long as one link in the chain is avoided, the accident may be avoided. Now, because there is no official authoritative investigation information disclosure, it is difficult to say which part of the problem is wrong.


  Q: A brief introduction to the Boeing 737 aircraft types


  There are many types of 737 passenger aircraft. The 737-800NG is a mature model that has been airworthy, which is different from the 737 max that has suffered two accidents in a row. The 737max is due to defects in the improved software and problems in the verification and airworthiness environment. It was grounded after two accidents, and has been re-airworthiness since then, and has now returned to service.

  General aircraft accidents, if it is the cause of the aircraft itself, it may be a one-time problem, or it may be a common problem related to the aircraft type. This cannot be said that there is a problem with the 737 aircraft.

  If some models have possible defects, they will be improved in time after the problem is found, because there will be maintenance and inspections for each flight, and changes will be made in time after problems are found. If a common problem is found, a notification should be issued, or even the plane should be grounded for complete improvement. This requirement is very strict.


  Q: After a plane crash, it is often seen in the news that the cause of the plane crash can be deciphered from the black box. Why is this? Is the black box critical?


  This black box is commonly known as a flight recorder. The earliest time in 1954, American airlines required the installation of a voice recording system in the aircraft cabin. At that time, it was a tape, which was to record the pilot's in-cabin calls. Airborne equipment is installed in a relatively common standard black square box, which is relatively stable. It was called a black box at that time. Later, after the 1960s, it was changed to orange-red.

  It records the voices of everyone's calls, which allows people to analyze what problems may have occurred. With the development of computer storage capabilities, the recorded data is now more comprehensive. Then there is the data of all the sensors in flight, including attitude angle, angle of attack, airspeed, ground speed and various flight states, such as electrical state, engine state, engine fuel supply, deflection angle of control surface, etc. , will record a lot of data. In this case, in the event of an accident, the black box is crash-resistant, it has been rigorously tested, and it is resistant to fire and shock.

  This time I saw that the passenger plane of China Eastern Airlines fell into the mountain. It should not be difficult to find the black box. In addition to the conspicuous color, it also has a beacon, which can transmit radio signals, allowing you to quickly find it. If the data is not damaged, after the experts After analysis, I believe that the cause of the accident will be located relatively quickly.

  Of course, there may also be data loss or some special situations not recorded by the flight recorder, which is difficult to say. But under normal circumstances, the flight recorder will record a large amount of data that may reflect flight problems. After data analysis, it will be very helpful for accident investigation.


  Q: Why can't the data in the black box be synced to the cloud?

  A: The amount of data is very large. If it is transmitted to the cloud, it requires high communication bandwidth, which is difficult to achieve at present. In addition, there are also data security issues. Some data, such as longitude and latitude, altitude, speed, etc., can be received by the air traffic control transponder.


  Q: Basically, this kind of disaster can only be solved through the black box. Is there only one way?


  This is not the only way. For example, if there is a special situation during the flight, the pilot will often communicate with the tower, the control center or the air traffic control department. Or send the 7700 code and report the problem first. In this case, it is possible to have a preliminary understanding of the situation and what may have happened through the air-to-ground voice communication.

  Of course, the most scientific and most evidence-based data is the data in the black box. The records of this data are more objective, accurate and reliable.

  If the pilot survived or the passenger survived, a survey of survivors can also be used to see what may have gone wrong.


  Q: When flying to the sky and encountering such a dangerous situation, is there really nothing that passengers can do? There's no way to save yourself?

  A: If the plane crashes or makes an emergency landing, it is very difficult for our passengers to have the opportunity to save themselves, because you are in a moving body, and the only way to save yourself is to lower your head and hug your legs as required to minimize the impact force. Open the window and jump down, and then there is no parachute, so it is said that the passenger has little possibility of self-rescue when a civil airliner crashes. You can only minimize the damage you suffer in the process, including taking off your glasses and high-heeled shoes to avoid damage to the body caused by foreign objects caused by the impact, and there is nothing else you can do.


  Q: Why are there only life jackets but no parachutes on the plane? Wouldn't it be better to have a parachute per person? Once you have a problem, open the window and jump off, can't you?


  The life jacket on the plane is for the passenger plane to fly at sea, and it is required to be equipped with this kind of water life-saving equipment, which can be used in case of emergency landing at sea or water.

  As for the parachute equipment, the cabin of a civil airliner will be pressurized, and it is difficult for you to get out of the cabin. If you want to parachute, you must open the cabin door, right? Skydiving is also learned, and you also need to have skills. Generally, it is very difficult for passengers to survive skydiving. If you jump into the woods if you don’t jump well, there will be disasters. Equipped with a parachute, as well as the weight problem, it will bring additional weight to the aircraft. Moreover, the aircraft itself is a very safe means of transportation, and a disaster accident is inherently a small probability event.

  Of course, there are some small navigable planes, such as those that take one or two people, and they have parachutes. When the plane encounters a problem or breaks down, you can use the parachute to land the plane. For large civil airliners, the direct use of parachutes to land will be very expensive if implemented, and the efficiency may not be very high. A high-cost method is used to deal with a very small probability event, from the commercial operation of the airline. In terms of cost, it may not be completely suitable.

  Although the technology is feasible, it may be unbearable for everyone as a consumer at that time. For example, if you install a parachute on the entire plane, the cost of seven, seven, or eight will add up, and everyone will not be able to get on the plane. This is a complex system engineering problem.


  Q: It has always been said that the plane is the safest means of transportation, and the probability of safety accidents is very low. How to understand this statement?


  Don't panic. When an aircraft flies into the sky, once any fault occurs, it is likely to cause a crash. Therefore, in the international civil aviation industry, the manufacturing requirements for aircraft are very strict. First of all, they must pass airworthiness and require the aircraft to meet the minimum safety standards. Generally speaking, the requirements The accident rate of the whole aircraft should be in the power of 10-9. Compared with road traffic, because they travel a lot, the probability of accidents will actually be higher than that of aircraft such as airplanes.

  When designing aircraft such as airplanes, safety and possible accident rates must be considered, so you must have two engines. If one fails, the other can maintain basic flight and landing. The airborne equipment is also three-redundant and four-redundant. The so-called redundancy configuration is to ensure safety through the joint work of multiple systems, so the probability of simultaneous failure is very low, because it is connected in parallel. relation.

  Therefore, the safety of civil aviation aircraft design is still very high, and generally no accidents will occur, or the probability of accidents is very low.

  Some people say that you are talking about 10 to the negative 9th power. This is difficult for everyone to understand. Here is an analogy. It is roughly equivalent to a family. Four generations from grandfather to father to son are flying 24 hours a day, 365 a year. The whole day is on the plane, and it is not necessarily that someone will catch up with a crash accident. This means that the probability is relatively low.