flight MU5735 Photo:CFP

China's aviation regulator released a report to disclose the latest progress on the China Eastern MU5735 crash probe on Monday, one year after the incident happened, saying that a technical investigation team has carried out a great deal of work on the case including onsite inspection, personnel interviews and experimental analysis, but since the case is "very complicated and extremely rare," the investigation is still ongoing.

Chinese experts said that it is a common requirement and practice in the international civil aviation industry to disclose relevant investigation progress information to the public on the anniversary of the incident. But the disclosure is determined by the actual complexity and progress of the investigation, and the current situation indicates that the investigation will take a longer time, experts said.

The report, which was released by the Civil Aviation Administration of China (CAAC), said it will continue to carry out investigation work and release relevant information in a timely manner according to the progress of the investigation.

China Eastern Boeing 737-800 with 132 people onboard crashed in South China's Guangxi Zhuang Autonomous Region on March 21 last year.

The technical investigation team has conducted detailed inspections on the wreckage of the aircraft to determine the possible working status of the aircraft's key control components before the crash, conducted experiments on more than 100 significant pieces of wreckage, and analyzed the cause of damage, read the statement.

It also carried out investigations into maintenance, airline organization and management work, as well as air traffic control services, airport ground support, and security checks and loading of passengers, luggage, cargo, and dangerous goods. Investigations into the final flight status of the aircraft based on relevant data analysis were also carried out, CAAC said.

The regulator said in the Monday statement that in accordance with both domestic and international industry rules and together with the relevant parties, it has conducted an in-depth, detailed and rigorous technical investigation into the crash over the past year.

Historically, Air France AF447, Ethiopian Airlines B737MAX and other accidents have issued interim reports or interim statements to introduce the progress of the investigation and respond to the concerns of the families of the victims and society, experts said. Experts noted that the investigation cycle of large-scale transport aviation accidents often takes more than one year, which is mainly due to the technical complexity and uncertainties faced by the investigation. 

Statistics show that among the more than 1,000 commercial aviation accidents that occurred in the global civil aviation industry in the past 30 years, only 25 percent of them had the final investigation report within one year.

The release came one day ahead the first anniversary of the crash. It is not only a response to public concerns, but also follows the general requirements and practices of the international civil aviation industry, Shao Quan, deputy dean of the College of Civil Aviation under Nanjing University of Aeronautics and Astronautics, told the Global Times on Monday.

Annex 13 to the Convention on International Civil Aviation said that the country conducting an accident investigation must make the final report publicly available as soon as possible within 12 months, if possible. If the report cannot be released publicly within 12 months, the country must publicly release an interim statement on each anniversary of the event.

The report covered the key parts of the investigation work, such as the search, identification, inspection, and experimental verification of the wreckage, and the qualification and ability of the crew members, which are the key steps of the overall investigation, and also an important basis for supporting subsequent research and analysis, and this will take a lot of time, experts said.

The current situation indicates that the accident is very different from previous ones, experts said. After the plane fell to the ground at high speed, it almost completely disintegrated, and the wreckage was tiny and scattered, greatly increasing the difficulty of on-site search and investigation and wreckage evidence collection.

According to accident investigation procedure, the investigation team needs to identify all the found wreckage and conduct detailed inspection and experimental analysis on the significant wreckage in order to determine the failure mechanism and the working status of the final stage, and provide evidence for the follow-up investigation and analysis, which is very complicated professional work, Gao Jun, an expert from the training and flight security department at the China National Aero-Technology Import and Export Corporation, told the Global Times on Monday. 

Other aspects of the investigation are also proving complicated, requiring the investigation team to carry out rigorous, objective and in-depth work to ensure that the final conclusion can stand the test of history, Gao added.