[The Epoch Times, March 30, 2022](The Epoch Times reporter Xu Manyuan in Los Angeles reported) All 132 people on board China Eastern Airlines flight MU5735 have been confirmed dead. The company’s system and various flight safety issues have also been widely discussed and discussed by the public.
A CCTV documentary with a total length of nearly 5 minutes and titled “Repair of Pickle Fork of China Eastern Technology Yunnan Branch” surfaced recently, and was first forwarded on the Internet by Jiang Feng, a senior self-media person. Currently, mainland media are surging news. The original report on the website has been removed. The film, produced by China Eastern Airlines, promotes the company’s process of repairing the Boeing 737-800NG forks on its own, but it also shows the potential problems of China Eastern’s maintenance team.
Sky, who has nearly 20 years of experience in flying aircraft, has a pilot’s license (ATPL), and currently lives in California, said that because he graduated from a professional aviation university, he has more time to study than ordinary pilots and has a wider range of knowledge. He personally owns two small planes, and he also conducts maintenance on his own, so he has a certain understanding of aircraft maintenance.
After watching the promotional video of China Eastern’s self-maintenance, Sky felt a little “surprised” and raised several doubts.
China Eastern Airlines self-maintenance and self-promotion
The documentary quoted a 2019 CCTV news report, saying that Boeing recalled about 50 aircraft with “fork” cracks globally, and two Boeing 737-800NGs of China Eastern Airlines were also in need of repair. However, it will take at least six months for the plane to be sent to Boeing’s maintenance depot in Victorville, California. After assessing economic losses and operating costs, China Eastern decided to repair it on its own.
Boeing’s public information did not consult the information authorizing China Eastern Airlines to carry out maintenance. However, in the self-recognition and publicity documentary of China Eastern Airlines, it was mentioned that the repair project was highly recognized by Boeing support engineers, and Boeing approved the China Eastern Airlines project as a self-developed maintenance plan.
From the documentary, we can see the picture of China Eastern’s maintenance team making every effort to prepare and operate.
Sky: Manual “step-by-step reaming” method is rare
In 2019, airlines in Indonesia, South Korea, Australia and other places successively discovered “fork” cracks caused by metal fatigue in the fuselage and wings of the Boeing 737-800NG. Therefore, Boeing conducted global inspections and removed all cracks. The plane was sent back for maintenance.
Sky said that the issuance of the Airworthiness Directive (AD) to recall the aircraft for inspection and maintenance is a very serious problem, but because Boeing has the corresponding maintenance capabilities, the repair will not cause problems and accidents, and the Boeing 737-800NG is relatively Mature models are also aircraft models that are considered quite safe by the industry.
There is a “fork” crack, and the parts that need to be repaired and replaced are near the flank of the aircraft. The difficulty lies in the positioning of the new parts and the drilling of two key structures. This replacement procedure is complex, requires a lot of engineering work, and also requires an aviation sheet metal team on the “exclusive” model.
According to the explanation of China Eastern’s promotional video, when making 25.43mm holes, because there were no “supporting” tools, the China Eastern Engineering team adopted the self-developed manual “step-by-step reaming” method to ream the holes. Sky said that the manufacturing of the aircraft is very precise, and each hole must withstand a lot of pressure. If there is an error in the hole spacing, it will definitely affect the pressure that the aircraft can withstand during flight.
He said that most aircraft manufacturers use computerized instruments to accurately measure the data, and use precise drills to drill holes, which is rare “by hand”. But because he didn’t see the real thing, he couldn’t judge whether the drilling was accurate, or whether it was safe, but it was indeed different from the way he was exposed to aircraft maintenance.
Sky said: “My small planes will be repaired by myself, using screwdrivers, but I have never seen a large passenger plane.” Whether the manual operation can achieve the drilling accuracy required by the plane is worrying. Because the distance between holes for aircraft assembly must be accurate, he said for example: “It’s like genuine Lego blocks, the tenon is very strong, but if you buy other copycat brand blocks, it will be different.”
The fork is a suspension system that connects the fuselage to the wings and withstands the stress and torque loads that bend the structure during operation. It is designed to withstand 90,000 life cycles – the entire lifespan of a Boeing 737-800NG.
Sky said that every small part of the aircraft needs to bear a lot of pressure, not ordinary aviation materials, especially the aircraft structural parts, and even the screws connecting the fuselage and the wings.
Sky further explained that these parts as a whole have to withstand at least an average maximum take-off weight (MTOW) of 174,200 pounds for an excessively hard landing, so most of the aircraft parts come from Boeing’s original factory, because there are not many factories in the world that can produce parts that meet the standards. Qualified, an accident occurs, the production factory will also bear a lot of responsibility.
Are the materials and technologies used in aircraft repair up to standard?
A CCTV documentary commended China Eastern for completing the repairs while the tools and equipment fell behind the Boeing team. But Sky believes that the backwardness of tools and equipment is only a superficial problem, and whether the aircraft materials and engineers used by China Eastern Airlines can reach the level of Boeing is the key.
Sky said: “Aircraft safety is very important, hundreds of lives, no joke!” Aviation metal used in aircraft has the characteristics of hard and light weight, a small piece of load-bearing accessories may cost thousands or more than 10,000 dollars; advanced aviation sheet metal There’s a reason why a division’s salary is very different from the average car sheet metal worker.
Sky said: “The aviation sheet metal engineer of this structure is a little more difficult than the general aviation sheet metal engineer. They not only need to be familiar with aerodynamics, but also need to understand the structure of this type of aircraft and need to pass the examination to obtain the certificate.” China Eastern Airlines repairs Boeing by itself The 737-800NG may really reduce operating costs and expenses, but he has reservations about whether it can achieve the required level of safety and professionalism.
Although Liu Xiaodong, head of China Eastern’s propaganda department, issued a statement on the question of the accident of China Eastern Airlines flight MU5735 and the hidden danger of “shift fork assembly” maintenance, he said that the aircraft maintained by China Eastern had withdrawn from the fleet on September 8, 2020, not this accident. aircraft B1791.
But according to the famous rule of American safety engineer Herbert William Heinrich: “When an enterprise has 300 hidden dangers or violations, it is very likely that 29 minor injuries or failures will occur, and there will be 1 serious injury or death accident. “All major security incidents are not sudden, but cumulative, with many symptoms accumulated.
Sky said that the China Eastern Airlines flight MU5735 air crash actually has many omen. In order to avoid such a tragedy from happening again, airlines and relevant units should submit the maintenance and repair records of the aircraft, so that experts in the industry can make professional judgments and let the public Can fly more safely.
Responsible editor: Yang Yihui#