With the successive discovery of two "black boxes", the search for important evidence of the flight accident of the "3.21" China Eastern Airlines MU5735 aircraft has basically come to an end.
Many mysteries remain to be solved.
How long will it take for the final survey results to come out?
The fatal accident rate of aviation flight is getting closer and closer to zero. Will it be equal to zero one day?
On some issues that people are generally concerned about, a reporter from China Youth Daily and China Youth Daily interviewed Wang Yanan, editor-in-chief of Aviation Knowledge, and Zhang Zhonglin, a commentator of civil aviation.
Three key 'witnesses' in flight accident investigations
As the key evidence in flight accident investigations, the "black box" is not actually black.
Its appearance is bright orange, which makes it easy to find it as soon as possible after an accident.
The protective layer of the "black box" is made of strong materials such as steel and titanium to protect critical information even in the event of a serious accident.
According to the requirements of the International Civil Aviation Organization (ICAO), the "black box" must withstand a shock force of 3400G and a high temperature test of 1000°C.
Searching for "black boxes" is not only the primary task of flight accident investigations, but also one of the difficulties faced by previous investigations.
On June 1, 2009, Air France Flight 447 crashed en route from Rio, Brazil to Paris, France, killing all 228 people on board, making it the worst air disaster in Air France's history.
It was not until two years later that investigators retrieved the "black box" that had been sleeping for a long time from the bottom of the Atlantic Ocean, and then found the cause of the pilot's error that caused the plane to lose control and crash into the Atlantic Ocean.
Wang Yanan said: "The 'black box' of Air France 447 provides the strongest support for the accident investigation."
At a press conference held on March 28, Zhu Tao, the aviation safety inspector of the Civil Aviation Administration of China, said that the decoding of the two "black boxes" of MU5735 is in progress, but relying only on the data provided by the "black boxes" is often insufficient. In order to restore the whole truth of the large-scale air disaster.
While advancing the decoding work, the Civil Aviation Administration is collecting as much information as possible.
"Flight accident investigation is a very rigorous job, and at least three pieces of evidence need to be obtained. One is the 'black box' data, the second is the wreckage at the scene, and the third is the information obtained from the external investigation. The three must be able to confirm each other." Wang Yanan said These three aspects of evidence are compared to three "witnesses". "No one can be trusted. The conclusion can only be established when the three "witnesses" agree." Zhang Zhonglin compared the accident investigation process to solving a case: "For example, The 'black box' is monitoring, the wreckage collection is the investigation of the crime scene, and the investigators are the forensics. Only through the clues and monitoring playback of the scene can the process be ascertained."
Obviously, the "black box" is the most important part of the process of "solving a case", but it is not the whole.
For example, the "black box" cannot record the process of the aircraft body's metal fatigue leading to fracture, and some mechanical failures will not be recorded by the "black box".
In the blind spots that are not covered by the "black box" data, the wreckage becomes the key evidence in the accident investigation.
"The wreckage can explain a lot of problems. For example, a detailed study of the wreckage can reveal whether the aircraft was damaged due to a collision or disintegrated in the air." Wang Yanan said that the distribution pattern of the wreckage on the ground after the disintegration of the aircraft in the air is similar to that of the complete aircraft. The distribution pattern of the fall apart after contact with the ground is completely different, and the degree of damage is also different.
The information obtained from the peripheral investigation can also provide some reference for the accident investigation.
Taking MU5735 as an example, in a video circulating on the Internet, the plane fell to the ground in a near-vertical attitude; while some witnesses in the nearby villages said that the plane dived at a certain angle.
Zhang Zhonglin believes that the aircraft is in a vertical dive in the video because the shooting location is directly behind the aircraft, and the inclined trajectory cannot be seen.
Although the video is flat, the world is "stereoscopic and three-dimensional".
Wang Yanan believes that neither video nor eyewitness accounts can be used as the final basis, because accident investigation cannot be judged by human senses, and the most reliable data is the "black box".
How long does it take to investigate a flight accident?
In December 1944, 52 countries signed the "Convention on International Civil Aviation" in Chicago, USA, and established the International Civil Aviation Organization (ICAO).
As of March 2019, a total of 193 countries have acceded to the Convention, including all UN member states except Liechtenstein.
According to ICAO regulations, within 30 days after the flight accident, the country in charge of the investigation should submit a preliminary report to ICAO; within one year after the accident, the country in charge should submit a final investigation report to ICAO.
In Zhang Zhonglin's view, ICAO's regulations on investigation reports are principled rather than mandatory, and whether they can be implemented depends on specific circumstances.
Still taking the Air France 447 crash as an example, "It took two years for the 'black box' to be retrieved. How could a report be issued within 30 days?" Wang Yanan also believes that ICAO is actually only asking for a summary of the previous stage of work. , flight accident investigation cannot stipulate a "time limit to solve the case", in that case, "accident investigation is not a technical problem".
MU5735 collided violently with the ground, and both "black boxes" were severely damaged. One of the internal memory chips was damaged and had to be repaired first, which made the investigation much more difficult.
Wang Yanan estimates that if the chip can be repaired as soon as possible, the accident investigation should be able to produce results within half a year, and if it does not go well, it will take longer.
Throughout the history of human flight, clear conclusions can be drawn from most accidents, but there are also some air accidents that have become permanent unsolved cases due to insufficient evidence.
For example, the MH370 accident that caused a global sensation in 2014, the wreckage of the plane and the remains of passengers have not yet been salvaged.
Zhang Zhonglin believes: "The air crash investigation may not always have results, and may not necessarily have correct conclusions. Some air crash investigation conclusions may be overturned by new discoveries."
Is the plane safe?
"The investigation procedures for every flight accident are actually the same, but the problems they face are different." Wang Yanan said that some accidents have relatively simple causes, such as sudden mechanical failures that directly lead to air crashes. More often, technical failures are related to Human factors are intertwined.
"In recent years, although the flight accident rate has declined, the reasons are still similar to those of 30 or 40 years ago. Apart from being shot down and hijacked, it is nothing more than improper maintenance of the aircraft, inadequate pilot safety style, and design defects," Zhang Zhonglin said. For example, last year's flight accident in Sanfoqi, Indonesia, was caused by mechanical failure.
"There is nothing new under the sun, similar air crashes in history, back and forth are all those reasons."
In 1990, James Risson of the University of Manchester in the United Kingdom put forward the theory of the "Swiss cheese model" in his psychology book "Human Error", which is also known as the "air accident model" theory.
According to this theory, organizational activities can be divided into different levels, each with certain loopholes, like Swiss cheese.
Accidents ensue when unsafe elements act like a beam of light through vulnerabilities at all levels.
There is also a famous theory in the field of aviation safety called "Hain's Law".
According to this theory, behind every serious accident, there must be 29 minor accidents, 300 near misses and 1,000 hidden dangers.
"Actually, accidents are like a pyramid. Air crashes are the top of the pyramid, and all kinds of unsafe behaviors are unsafe behaviors at the bottom of the pyramid. From hidden dangers, ordinary accidents, serious accidents to air crashes, the pyramid goes up step by step." Zhang Zhonglin said.
So, can flight accidents be completely nipped in the bud by taking measures to prevent microscopic and progressive development?
Wang Yanan believes that no engineering product made by humans can achieve absolutely zero failures or zero accidents.
In the past 20 years, the global civil aviation safety curve has been rising, and the overall trend is getting better and better.
But it is against scientific laws to make the safety accident rate completely equal to zero. "We can only reduce the accident rate and reduce it, and it is infinitely close to zero."
According to data released by IATA in March 2021, from 2016 to 2020, there were 1.38 accidents per 1 million flights worldwide, and the average risk of death from air travel was 0.13.
A person must fly a plane every day for 461 consecutive years to encounter a flight accident with one fatality;
In other words, the vast majority of people will not experience any fatal flying accidents in their lifetimes.
Before the accident of MU5735, the safe operation of Chinese civil aviation had reached 4,427 days, which is the longest safe operation record in the world.
"Any plane in China can be taken with confidence, because the Civil Aviation Administration will not let unsafe planes fly into the sky." Zhang Zhonglin said that according to ICAO statistics, the incidence of air crashes per million hours in China is far lower than Global Air Crash Average, "Of course, the lower the number, the better."
Wang Yanan believes that in terms of probability, the possibility of a flight accident will always exist, but the probability is very small.
In fact, the number of fatalities caused by airplane accidents is much lower than that of road traffic accidents.
According to the 2020 Statistical Bulletin of National Economic and Social Development, the number of deaths per 10,000 vehicles in road traffic accidents is 1.66.
Up to that time, in the past 12 years, no one has died in China's civil aviation due to a flight accident, and the safety of civil aviation is much higher than that of road transportation.
However, the good operating record in the past does not mean that the regulation of the aviation industry can be relaxed.
Wang Yanan pointed out that for the public, it is difficult to improve aviation safety through individual actions, and it is necessary to rely on government agencies to monitor whether the implementation of safety regulations in the entire industry meets the standards, whether the aircraft can maintain airworthiness anytime, anywhere, and so on.
He said: "Why do institutions like the FAA (Federal Aviation Administration) or the Civil Aviation Administration of China appear? It is because aviation safety cannot be supervised by individuals. The government must come forward and supervise the entire system on behalf of consumers."
This newspaper, Beijing, March 30th
China Youth Daily and China Youth Daily reporter Hu Wenli