Boeing 737 MAX's go-around is approaching, is it really safe after the improved design?

Approval by the regulatory agency means a safe judgment, but more homework is needed to restore confidence

article | Caijing reporter Liu Wanyuan and Wang Jingyi

editor | Shi Zhiliang

grounded for nearly two years, Boeing (NYSE: BA) 737 MAX's go-around is getting closer.

Recently, as the highest local regulatory agency, the European Aviation Safety Agency (EASA) and the US Federal Aviation Administration (FAA) have made it clear that this aircraft has made adjustments sufficient to ensure safety and can be used before the end of 2020 Europe and America go around. American Airlines (NASDAQ: AAL) has even arranged a 737 MAX flight from Miami to New York starting December 29. A relevant person from Boeing China confirmed to the Caijing reporter: “It is expected to obtain the necessary regulatory approvals in time in the fourth quarter and support the expected delivery. Of course, the regulatory agency will finalize the actual time.”

is on a global scale In the first country to ground the Boeing 737 MAX, Feng Zhenglin, director of the Civil Aviation Administration of China, publicly responded on October 22. There was no set timetable for the go-around, but three principles must be met: design changes to the aircraft must be approved for airworthiness; the pilot; Sufficient and effective training must be obtained; the investigation conclusions of the two accidents must be clear and the improvement measures must be effective.

went around in winter, the only uncertainty is the specific date. However, the question still lingers in the public minds, is the Boeing 737 MAX really safe?

Professor Huang Jun of the School of Aeronautics and Astronautics, Beijing University of Aeronautics and Astronautics, told Caijing reporter that if the 737 MAX can regain the FAA's airworthiness certification, the flight safety of the aircraft can be guaranteed. But he also pointed out that "in theory, no aircraft is 100% safe. From the perspective of the modification of the MCAS system, the risk of accidents due to this component is now avoided." For ordinary people, the 737 MAX The go-around will have no actual impact for the time being.

"Even if it gets the airworthiness certification, the domestic airlines will not go back to the 737 MAX for a while, because the current capacity is enough, if the capacity is too much for the go-around, after all, there is no peak travel season in China." Aviation consulting company Li and Li The founder Li Hanming told a reporter from Caijing.

Affected by the new crown pneumonia epidemic, the airline's attendance rate has not yet returned to the level of previous years, and it has no intention to put a high-capacity aircraft such as the 737 MAX into operation. The 737 MAX has about 178 seats, which is the largest single One of the channel planes.

MCAS system design flaws have been resolved

In October 2018, a Boeing 737 MAX flight of Lion Air from Indonesia crashed in Java, killing 189 people. In March 2019, the same Boeing 737 MAX, an Ethiopian Airlines passenger plane lost contact and crashed 6 minutes after takeoff, killing 157 people on board. There were two crashes within a few months. The Civil Aviation Administration of China took the lead in issuing a no-fly order, suspending the commercial operation of the Boeing 737 MAX. Countries such as the United Kingdom, Malaysia, and Australia have also suspended the 737 MAX. After the Ethiopian Airlines crash, Dennis Muilenburg, then CEO of Boeing, admitted that the cause of the crash was a design flaw in the MCAS (Enhanced Maneuverability) system installed on Boeing 737 MAX models.

wants to explain what the MCAS system is and why it needs to be installed. It is necessary to review the design logic of this model.

Boeing 737 MAX is a derivative model of Boeing 737 equipped with the new engine LEAP-1B. Compared with the engine configuration of the previous series, the LEAP engine is larger. However, due to the insufficient height of the landing gear in the original design of the Boeing 737, and the lack of space for hanging the LEAP engine under the wings, in order to give full play to the engine's efficiency, the installation position of the engine needs to be higher and forward.

However, the new engine weight, size and position will damage the aerodynamic performance of the original configuration, especially in the high angle of attack state-the vortex leaving the engine compartment produces lift, and the engine compartment is located before the center of gravity, The aircraft produces a slight head-up effect, and the drag of the control stick will be reduced, but this is exactly the opposite of the pilot's normal operating experience.

Chen Jianguo, a senior civil aviation captain who has flew the 737 MAX many times, told Caijing reporter that pilots flying an airplane are connected to driving a car from the perspective of power-assisted design. The turning hours can be turned with a small amount of force, but the greater the turning range. Larger, the greater the force and angle of turning the steering wheel must be, otherwise it is easy to over-steer.

Chen Jianguo said: "Aircraft lever operation is also a similar requirement. When the aircraft pitch angle becomes larger and larger, the pilot feels that the force required to carry the lever should be larger and larger, not smaller and smaller, which is consistent with the conventional flying experience. It’s the opposite, and it’s easy for the pilot to subconsciously bring the angle too large and cause the plane to stall.”

When it is difficult to control the plane with normal driving habits, Boeing introduced automatic control functions to ensure the stability of the plane: on the original control system Add a set of software "patches", that is, the MCAS mobility feature enhancement system. Aviation expert and permanent director of the Chinese Society of Aeronautics Zhang Juen concluded that the basic design logic is to monitor the angle of attack (Angle of Attack) data, and make the system automatically turn on when the angle of attack is large enough and the flaps have been retracted. , To adjust the stabilizer and lower the nose.

However, this patch system installed in order to maintain the stability of the aircraft has become the chief culprit in the two crashes of the 737 MAX due to fatal flaws in the design logic.

Li Hanming told the Caijing reporter that for a system, there are two principles: do what should be done and not do what should not be done. MCAS itself is an automatic operation system, there is no problem when the sensor data correctly conveys the information, but when the sensor data does not meet the conditions, the effector should remain stationary.

In fact, the Boeing 737 MAX does have two angle of attack sensors, but the MCAS judgment logic does not compare whether the data of the two sensors is correct, but when the data of one of the sensors indicates that the angle of attack is too high, MCAS will be activation. However, if the sensor fails or the data is incorrect, MCAS will continue to function and constantly adjust the "trim", causing the aircraft to dive and crash.

"MCAS relies solely on the sensor data of the angle of attack sensor. When the sensor fails, it also makes the wrong decision." Li Hanming said. Another fatal flaw of

is the pilot's ignorance of the MCAS system.

According to media reports, Boeing provided airlines with the angle of attack warning light (which lights up when the two sensor data is inconsistent) and the angle of attack indicator that are compatible with the MCAS system, but they are not standard on the 737 MAX. Customers need to "add money" "Buy separately. The two crashed planes of

did not have optional warning lights and indicators. Before the first air crash, all 737 MAX pilots were never told that the new model was equipped with the MCAS system. The flight manual did not mention it at all, nor did the flight training teach any solutions to such situations. When MCAS is automatically turned on by mistake, it will cause the aircraft stabilizer trim system to operate at high speed, but the cockpit will only display the trim wheel quickly rotating. The pilot does not know what triggered it, let alone how to manually shut off the MCAS system.

According to Boeing’s previous disclosures, a series of improvements have been made to address the design issues of the 737 MAX’s MCAS system:

1. The flight control system will compare the data of the two angle of attack sensors at the same time;

2. The angle of attack warning will be added to the aircraft’s main display Among them, it will be installed for customers free of charge;

3. With the flaps retracted, if the difference between the two angle of attack sensors is 5.5 degrees or more, MCAS will not be activated, and the angle of attack warning will Prompt the pilot;

4. If the aircraft's angle of attack is too large, the MCAS will only be activated once for each angle of attack warning;

5. MCAS can never give instructions to the horizontal stabilizer that the flight crew cannot offset by pulling back the joystick. The pilot will be able to overtake MCAS through the lever and manually control the aircraft and continue to climb.

In this regard, Chen Jianguo believes that by changing the operating logic of the MCAS system and the configuration of related software and hardware systems, it is sufficient to avoid the risk of the MCAS system in the two accidents. "From the perspective of pilot training and operation, as long as you understand the working principle of the system and know how to turn off the system, it is very simple to use the MCAS system effectively and safely in flight." Z1z

Huang Jun told the reporter of Caijing, If the 737 MAX modification plan canBy passing and regaining the FAA's airworthiness certification, the flight safety of this model can be guaranteed. But he also pointed out that obtaining airworthiness certification only allows the aircraft to meet the minimum standards for safe flight.

"A series of serious errors jointly caused"

The design flaws of the MCAS system itself directly led to the 737 MAX crash. However, according to the investigation report on the Boeing 737 MAX series released by the US House of Representatives on September 16, there were two previous 737 MAX crashes. It was caused by "a series of serious mistakes" made by Boeing and the FAA.

The report reviewed Boeing’s engineering and technical design issues. The chairman of the House Transportation Committee, Peter DeFazio, told the media, "The conclusion of the analysis is that if the MCAS design flaws in the 737 MAX are not corrected, as many as 15 fatal accidents may result in the entire fleet life. "Z1z

puzzled the public as to how the MCAS system that caused the two crashes passed the FAA's airworthiness certification?

"The FBI and Boeing concluded that the 737 MAX meets the'certification' standard. This so-called certification killed 346 people within a few months. Compliant with the certification is not safe. There are obviously problems with this system and process. "De Fazio reprimanded.

In fact, the two air crashes were not caused by a single mechanical failure, technical error or improper management, but a series of technical assumption errors by Boeing engineers, lack of transparency by Boeing management, and serious inadequacy of FAA supervision.

The report analyzes that the urgency of cutting costs has affected countless decisions. The investigation found that in order to avoid the difference between the 737 series aircraft and the new 737 MAX model being sufficiently significant, "so that it is necessary to conduct simulator training for pilots of the new model" and adding one million dollars in cost to each aircraft, Boeing concealed the MCAS system of the new aircraft from pilots and users.

cost control includes choosing not to have a pilot warning system as standard. According to the report, "FAA accepted Boeing's argument about the impracticality and economic cost of installing the warning system-if it is installed, it may help pilots to operate the aircraft correctly in Lion Air and Ethiopian Airlines accidents."

In addition, the report also revealed how Boeing's close relationship with the FAA affected its supervision. The first is "being an athlete and a referee". Many cases show that Boeing employees are authorized to perform work on behalf of the FAA, but they did not warn the FAA about potential safety and certification issues. The second is affecting FAA's decision-making. Documents submitted by multiple FAA officials show that FAA management rejected the recommendations and conclusions of FAA technical experts at Boeing's request.

For this report, Boeing responded that it had fully cooperated with the House Committee, and the design modification of the 737 MAX had been subject to in-depth internal and external review. A Boeing spokesperson said that Boeing has learned bitter lessons from the accident. “Once the FAA and other regulatory agencies confirm that the 737 MAX can go back safely, it will be one of the most thoroughly audited aircraft in history. Safety is full of confidence.” In addition, Boeing said that it has been working to strengthen the safety culture, rebuild trust with customers, regulators and passengers, and carry out internal reforms, “to make the voice of engineers stronger and more directly convey concerns to senior management. ".

Chen Jianguo pointed out that Boeing's previous risk assessment of MCAS had problems. Starting from the principles of risk management, risks that are extremely unlikely to occur but will cause great consequences do not require too much attention, such as two engines hitting a bird at high altitude at the same time. However, the failure of the MCAS system can cause catastrophic consequences, and the probability of errors in the system is not low.

From the pilot's point of view, he believes that Boeing's bigger mistake lies in concealing the installation of the MCAS system on the 737 MAX.

"When we heard that the crash of the 737 MAX was due to the MCAS system, all pilots were very angry. They were equipped with such a potentially lethal system and did not tell the pilots? In this state of unknowingly, the world has driven and boarded The people of the 737 MAX can only say that they were lucky enough to escape the catastrophe, because if they encounter the same system failure, they are likely to face the same ending as Lion Air and Egypt Air." Chen Jianguo told the Caijing reporter.

Europe and the United States are grounded late, go around early

On March 11, 2019, less than 20 hours before the Ethiopian Airlines plane crashed, the Civil Aviation Administration of China took the lead in the world to issue a notice requiring domestic airlines to suspend the 96 Boeing 737 MAX jets operated by them today. On March 12th and 13th, Europe and the United States were also grounded.

On the following March 21, 2019, the Civil Aviation Administration announced the suspension of accepting applications for the Boeing 737 MAX airworthiness certificate. Since civil aircrafts operated in Mainland China must hold three certificates including type certificate, production license and single airworthiness certificate at the same time, they cannot operate normally without one. This means that before the Civil Aviation Administration cancels this restriction, even Boeing Delivery resumes, and domestic airlines cannot accept 737 MAX models.

Airworthiness certification is usually a long process. When the 737 MAX 8 entered China, it took 15 months of airworthiness certification before it was finally approved. As for the status of the airworthiness certification for this return to flight, the Shanghai Aircraft Airworthiness Certification Center of Civil Aviation of China declined the reporter's request for an interview.

Feng Zhenglin recently revealed that the president of Boeing has approached him twice about the go-around. The Civil Aviation Administration of China has maintained technical cooperation and contacts with FAA, Boeing and the aviation regulatory agencies of the European Union.

China's civil aviation safety flight level is leading the world. As of 2019, China Transport Airlines has achieved a new safety record of 112 months of continuous safe flight and 80.68 million hours, and has achieved zero liability accidents for air defense safety for 17 consecutive years and 7 months.

Although the Civil Aviation Administration of China has not yet let go, there are more and more signs of Boeing 737 MAX going around.

Even though the aircraft can only lie down at present, the airline has not forgotten to do daily maintenance and maintenance. In September of this year, the aircraft maintenance company Shandong Taikoo just replaced the landing gears for several 737 MAX aircraft owned by Shandong Airlines, and selected elites from various departments, "for the 737 MAX aircraft to achieve a high level in the country after the go-around Maintenance has laid a solid foundation."

The United States expressed more direct support for the 737 MAX's go-around. FAA Director Steve Dickson personally tested the 737 MAX passenger plane on September 30 this year, trying to dispel the outside world's doubts about the 737 MAX passenger plane.

American Airlines also stated that after the 737 MAX airliner is certified, from December 29 to January 4, the company will use the 737 MAX to fly Miami to New York flights, initially once a day, and will consider launching more flight. American Airlines did not forget to remind: "We will make sure that customers know that they are flying on the 737 MAX."

Li Hanming told the Caijing reporter that the order of the 737 MAX in the world is the United States first, then Europe, and then Look at china.

On October 16, Patrick Ky, director of the European Aviation Safety Agency (EASA), said that the Boeing 737 MAX models have made adjustments that are sufficient to ensure safety and can return to the European market before the end of 2020. Patrick Ky said that after the test flight in September this year, the European Aviation Safety Agency is currently conducting the final document review and is expected to announce the draft airworthiness directive in November, followed by a four-week public consultation.

The agreement of European and American regulatory agencies is of great significance to the global return of the 737 MAX, because many countries and regions will directly accept the airworthiness certification results of these two agencies.

After all, China’s only professional aircraft airworthiness certification organization, China Civil Aviation Shanghai Aircraft Airworthiness Certification Center was only established 13 years ago. The two countries where the air crash occurred, Ethiopia and Indonesia, lacked independent airworthiness certification capabilities. The Caijing reporter checked the official website of the Ethiopian Civil Aviation Administration and found that since Ethiopia does not have the ability to design aircraft, the Civil Aviation Administration of Ethiopia only requires "access" to issue the aircraft that are manufactured by Boeing and other foreign aircraft that are only operated in Ethiopia. The airworthiness directives and other contents of China cannot carry out independent airworthiness certification like China.

Ethiopian Airlines CEO Tewolde Gebremariam has previously stated publicly that because the crew and passengers have lost confidence in this model, if the Boeing 737 MAX is to go around, they will be the "last airline to go around."

Is the Boeing 737 MAX safe?From a technical level, the approval of the regulatory agency means to give a safety judgment; but from the level of confidence restoration, it seems that there is still a lot of homework to be done.