The long-warming "Captain of China" is finally officially released.
On the day 3U8633 was in danger in 2018, it touched the hearts of countless people. This is a special treatment that can be called a miracle. Therefore, when it was put on the screen, the entire civil aviation industry had high expectations.
As the saying goes, "The layman is watching the excitement, while the insider is watching the doorway." Many viewers only know that the broken glass of 3U8633 caused a series of subsequent dangers, but few people know that this aircraft is an Airbus A319. The model, the falling windshield was supplied by Saint-Gobain, France.
In addition, there are more points worth pondering. For example, why does glass break? Is this glass accident of Sichuan Airlines accidental? These are all questions that need to be answered from a more professional perspective.
Why does the glass break?
Aviation glass is an important part of the aircraft. It not only acts as a transparent part, but also mainly involves maintaining the aerodynamic shape of the aircraft and the pressurization of the cabin. According to the installation position, it can be divided into cockpit glass and cabin porthole glass.
All aviation glass needs to be subjected to a series of rigorous tests before being installed and applied, and must have anti-impact and anti-crack properties.
In order to achieve the above functions, the windshield glass of the cockpit must be composed of multiple layers of glass. Generally, thermally tempered glass is the outermost layer, and the middle and inner layers are chemically strengthened glass. The layers are combined with PVB (polyvinyl butyral) or PU (polyurethane) or PVB+PU. This design is to increase impact resistance.
â–˛ Sichuan Airlines accident map / Dongfang IC
Windshield glass needs to be verified in three aspects in terms of structural strength:
(1) Ultimate strength verification;
(2) Damaged safety verification;
(3) Fatigue verification.
A technical expert working on the windshield glass of passenger aircraft told a passenger that for aircraft designed to operate at a height of no more than 13,700 meters, the windshield glass, as a component of the pressurized cabin, should be able to withstand 1.33 times the cabin pressure relief The pressure of the maximum setting value of the valve; and considering the safety factor of 1.5 times, an additional factor of 2 is needed to cover material performance fluctuations, long-term performance degradation, and environmental conditions. Therefore, in order to prove the ultimate bearing capacity of the windshield, needs to be tested under 1.33Ă—1.5Ă—2=4 times the maximum setting value of the relief valve (considering the upper limit of the pressure tolerance of the relief valve).
In addition, when any layer of the windshield itself is damaged, the windshield must be able to withstand the maximum pressure difference load and the critical aerodynamic pressure bearing capacity of the cabin, taking into account the influence of temperature; therefore, to prove the damage of the windshield The safety capability needs to be tested and assessed with a load of 2 times the pressure difference after the maximum use pressure difference and the maximum aerodynamic pressure difference in the cabin are superimposed with only a relatively weak and intact structural layer of glass.
The above-mentioned experts said that in special risks, the windshield must be proved to be able to withstand the impact of a 1.8 kg bird at the aircraft’s maximum sea level cruise speed to ensure that it does not penetrate, and at least the inner glass will not cause damage to the pilot. Out.
In addition to anti-impact, the windshield must also have the function of deicing and defogging. Therefore, the inner side of the outermost tempered glass is also equipped with a transparent conductive covering film-heating film, the device is to help the windshield deicing. A demister is installed in the middle of the inner glass.
According to the above situation, Shen Haijun, a professor at the School of Aeronautics and Mechanics of Tongji University, told Traveling Yike that there may be four major reasons for the break of the windshield glass. One is the impact of foreign objects in high-speed movement, such as birds, hail, etc.; the second is the problem of window frames and installation fasteners; the third is the quality of the glass; the fourth is the failure of the heating system.
According to the situation reported by the Civil Aviation Administration, Sichuan Airlines flight 3U8633 was climbing to an altitude of 9800 meters. The front windshield of the right seat of the cockpitSuddenly broke and fell off. The height of 9,800 meters is close to the stratosphere. Shen Haijun said that at such a height, the possibility of external impacts from flying birds and hail is very low.
However, this possibility cannot be completely ruled out at present. The above-mentioned windshield expert told a traveler that there had been bird strikes on the Chengdu-Lhasa route.
â–˛ Source / Xinhua News Agency
Window frame and installation fastener problems may also exist. The expert introduced that due to the Sichuan Airlines incident, the windshield window frame, pressure plate, and fasteners were left intact in their original positions, and there were no signs of defects in the window frame or fasteners. "The possible reason is that during the installation process, the windshield installation design requirements were not completely followed, which resulted in a high forced assembly stress on the windshield glass and possibly caused local damage to the windshield glass. During the long-term flight of the aircraft, A certain combination of high differential pressure load, flight load and forced assembly stress exceeds the rupture strength and causes sudden rupture, or the fatigue damage of the initial defect site accumulates, which eventually leads to sudden rupture.”
It is understood that Sichuan Airlines flight 3U8633 fell off The windshield on the right side of the machine is the original part of the machine. It was put into operation until the incident, and there was no failure record. If the installation problem is indeed caused after the investigation, then the responsibility for the accident is likely to be attributed to the Airbus Assembly Center.
The quality of glass cannot be ignored either. The aircraft involved in the accident was Airbus 319, which belongs to the Airbus A320 series and was delivered to Sichuan Airlines in 2011. If there is a defect when leaving the factory, the defect may be caused by fatigue load during the long-term flight.
The windshield of Sichuan Airlines flight 3U8633 is produced by the French Saint-Gobain Group. Saint-Gobain (China) Investment Co., Ltd. told a traveler that this was an extremely rare accident. The Civil Aviation Administration of China has organized investigations by relevant parties, and it is inconvenient to accept any interviews before the official investigation results are released.
Whether there is a failure in the heating system is also the focus of the investigation. A heating film is added in the middle of the windshield glass. If the heating system fails, there may be local short circuits and arcs (Note: A gas discharge phenomenon not only has a great destructive effect on the contacts, but also prolongs the time to disconnect the circuit) The problem, which in turn caused the aircraft windshield to break.
There are precedents for this issue. In October 2013, the Civil Aviation Administration of China issued an airworthiness directive requiring the inspection and replacement of the windshield heating joints for fixed windows. The CAD2012-MULT-02R1 airworthiness directive pointed out that several operators reported that several cases of burnt smell and/or smoke appeared in the cockpit during the cruise phase. The investigation found that the cause of these incidents was the burning of the end blocks of the windshield joint produced by Saint-Gobain. Involving A330 and A340 related models.
The above-mentioned windshield glass technical experts said that pilots have more say in when to replace the cockpit glass. If minor scratches or wear occur, after checking in accordance with the manual, it is confirmed that the conditions for continued use are met. The pilots and dispatchers may not require the replacement of the glass. Under normal circumstances, the service life of the cockpit glass can reach ten years.
The cabin porthole glass has such a high-strength load capacity compared to the glass without the cockpit, but it also has functions such as pressure resistance, and it is generally double-layer glass. In the past, most of the accidents of window glass breakage were caused by the impact of foreign objects.
Aviation glass accidents in history
There are similar precedents for aviation glass accidents in history. The most widely known is the British Airways accident in 1990. The survey results two years later showed that the main cause was poor maintenance management.
British Airways flight BAC1-11 5390 took off from Birmingham International Airport at 7:20 in the morning on June 10, 1990, and flew to Malaga, Spain. At 17,300 feet above Didcot in Oxfordshire, England, the windshield glass on the left side of the aircraft's nose broke and fell off. The captain was sucked out of the window and hung on the outside of the fuselage.A panicked flight attendant held his legs. Finally, under the operation of the co-pilot, the plane successfully landed at Southampton Airport at 7:55.
After the accident, the British Aviation Accident Investigation Office and other relevant departments (Air Traffic Control Office, Civil Aviation Administration, Royal Air Force Institute of Aviation Medicine) formed an accident investigation team to Information, crew members, aircraft damage, weather conditions, aircraft communications and recording equipment, medical pathology and other information have been comprehensively reviewed. The following are the focus and methods of the investigation. The
investigation team first conducted simulation tests and researches, inspected the specifications, size and area of ​​the fixing screws on the windshield, and inspected the screwdriver for repairing the windshield.
secondly reviewed the airworthiness certification of the aircraft, including: BAC One-Eleven aircraft type qualification, aircraft maintenance requirements, airline quality standards, maintenance engineer licenses, company authorizations, and maintenance manuals.
inspected the British Airways infrastructure again, and thoroughly investigated the airline’s quality supervision system, management roles in the quality supervision system, quality review process, maintenance control procedures, and ground handling reports.
finally investigated the management organization of British Airways in Birmingham, including organizational responsibilities, organizational equipment and facilities, air stations, inventory management procedures, quality assurance practice training, and E1022 procedures used in Birmingham.
The investigation team completed the investigation in two years. The investigation report provided by the British Civil Aviation Administration to a passenger showed that the windshield of British Airways Flight 5390 was replaced 27 hours before the accident. The investigator found that among the 90 screws installed in the windshield, 84 screws are 0.026 inches (1 mm) in diameter, which is smaller than the standard; the remaining 6 screws are 0.1 inches (3 mm) in length, which is much smaller than the standard. The standard is short, coupled with the influence of the reduced air pressure in the cabin, which eventually causes the glass to break and fall off.
The investigator revealed that because of the heavy workload of the engineers in the British maintenance department, they used the naked eye experience as the criterion of “as similar as possible” when selecting components, instead of referring to the aircraft maintenance files and the opinions of warehouse management personnel, which led to the accident. .
In addition to the above direct reasons, the British Civil Aviation Authority believes that there are indirect reasons. The investigation team believes that the safety of the maintenance task has not been highly valued, because only one person is responsible for the quality of the fixing screws, and the accessories are directly flying after installation and have not been tested.
The aircraft shift maintenance manager did not take care of the windshield glass installation process properly, had bad trading behaviors, did not comply with company standards and used inappropriate equipment, which affected the quality of maintenance and the judgment of failures. The local management department of British Airways did not monitor that the product samples and quality audits used by the shift maintenance manager did not meet the standards because they did not directly monitor the work of the shift maintenance manager.
Monopolized glass market
These rare accidents reflect the safety of aviation glass, and let more people understand the shortcomings of China's civil aviation industry parts production.
The global aviation glass supply is basically monopolized by three foreign manufacturers, namely France’s Saint-Gobain Group, UK’s GKN Company (LSE: GKN) and American PPG Company (NYSE: PPG).
Saint-Gobain Sully, a subsidiary of Saint-Gobain Group, is responsible for the production of aviation glass. For more than 50 years, it has provided glass products for mainline airliners, jets, regional airliners, helicopters, fighter jets and other aircraft around the world.
â–˛ Source / Saint-Gobain's official website
Saint-Gobain Suli's main customers are Airbus and Russia's Irkut Aircraft Company. The Airbus A320 family, A330, A340, A380 and Irkut’s MS21 all use Saint-Gobain’s aviationglass. China is also a major business development location for Saint-Gobain. According to a traveler, Saint-Gobain is a Class III supplier of COMAC. The ARJ21 aircraft produced by COMAC uses aero glass produced by Saint-Gobain.
British GKN company is another major aviation glass production giant in continental Europe. GKN Aerospace's GKN business is distributed in Europe and the United States. The products mainly involve aviation structure, propulsion system and aviation glass. GKN's current customers include Boeing, Airbus, and many aircraft operators.
The American PPG company, among the Big Three, provided windows for Ford Tri-Motor aircraft in 1927. Since then, it has been providing glass panels for the military. At present, Airbus, Boeing, Embraer, and Bombardier, the four largest aircraft manufacturers in the world, are all customers of PPG.
China’s aircraft industry is also accelerating its development, which will inevitably drive the rise of upstream and downstream industrial chains. However, in the field of aviation glass production, there has not yet been a breakthrough.
Compared with glass products such as automobile glass, aviation glass is extremely difficult to produce. GKN told Traveller that the technical barrier of aviation glass mainly lies in how to ensure transparency requirements. Aircraft windshields need to be laminated in a very clean environment to ensure minimal optical defects. In addition, aviation glass forming is also a unique technology, requiring special ovens, vacuum chambers, and tools such as five-axis machines.
Based on the existence of the above technical barriers, there are only a handful of aviation glass productions in the world.
Zang Shuguang, deputy dean of the Institute of Glass Science, China Academy of Building Materials Science and Technology, said in an interview with a traveler that the institute was able to produce aviation glass in the 1950s, and China Aviation Development’s 621 institutes can also Production of aviation glass. At that time, military aircraft and Yun-7 civil aircraft used aviation glass produced by the above two units.
However, due to the twists and turns of China's civil aircraft industry, civil aviation glass manufacturers have been lacking practical application experience.
Foreign aircraft manufacturers do not come to China to select suppliers, and they generally source materials locally. More importantly, civil aviation glass involves the issue of airworthiness certification. Foreign suppliers have passed the certification of the Federal Aviation Safety Agency or the European Aviation Safety Agency. Chinese glass manufacturers without airworthiness certification of the above organizations cannot enter the international giants. List of suppliers.
Zang Shuguang believes that if domestic civil aircraft adopt domestic aviation glass and pass the airworthiness certification, Chinese aviation glass manufacturers can enter the market.
First of all, the aircraft design unit must provide technical requirements for the glass enterprise, and the glass enterprise shall provide design solutions and manufacture samples. Then complete various tests and assessments. The test flight conclusion was obtained after the installation test flight. Glass companies can obtain airworthiness certificates individually or with the aircraft. The product can be installed on the corresponding model only after it has been approved by the airworthiness department and issued a certificate. In the process, the airworthiness department must intervene in advance.
However, China's civil aircraft industry has just restarted, and the reliability requirements for various components are relatively high. China Aviation Glass lacks practical experience, and there is no sufficient data to confirm its reliability. Therefore, the glass supply for Chinese civil aircraft still comes from foreign giants.
â–˛ Inside the C919 large passenger aircraft, domestic glass has been used for C919 portholes / Oriental IC
In recent years, AVIC Sanxin Co., Ltd. (002163.SZ , Hereinafter referred to as "AVIC Sanxin") has become a new force in special glass production. Founded in 1995, AVIC Sanxin focuses on the development of special glass deep processing and technology, curtain wall engineering and general aviation airport, photovoltaic glass and photovoltaic engineering.
According to "Hainan Daily", the high-end glass production base of Hainan AVIC Special Glass Material Co., Ltd. under AVIC Sanxin has settled in Hainan. The first-phase production base covers a total area of ​​641 mu, and there are 4 production lines that are regarded as key provincial projects.
Among them, Line 1 is the transformation project of electronic thin glass production line, Line 2 is the transformation project of ultra-white solar TCO glass production line, and Line 3 is the all-oxygen combustion production line Low-E coating energy saving projectGlass production line, Line 4 is aerospace and high-speed rail glass production lines, both of which are large projects with a daily output of 600 tons.
The C919 prototype independently developed and produced by China used aviation glass produced by AVIC Sanxin. AVIC Sanxin said that it has not yet formed a scale, and further orders are being confirmed. According to many people in the civil aviation industry, the prototype does not represent the final commercial use, and China's aviation glass production capacity needs to be improved.
Relying on China's civil aircraft production, aviation glass and other Chinese parts companies are expected to break the monopoly of European and American companies, but the road to master the most advanced technology and equipment is still long. Zang Shuguang said that civil aircraft manufacturers can allow aviation glass manufacturers to start from small pieces, accumulate experience, gradually cultivate and strengthen confidence in domestic products, and then expand the industry. (Editor in charge / Yang Peiqian)
