The problems of the Boeing 737 Max are a legacy of its past

Pilots light up some of the new Boeing aircraft by turning a button and activating two switches.

The Boeing 737 Max, the newest pbadenger aircraft on the market, operates differently. The pilots follow roughly the same seven steps as those used in the first 737 almost 52 years ago: they turn off the cabin air conditioner, redirect the airflow, start the engine, open the pbadage of the fuel, reverse the flow of air, they turn on the air conditioner and turn on a generator.

The 737 Max is a legacy of its past, based on systems from decades ago, many of which date back to the original version. The strategy of continuing to update the aircraft instead of starting from scratch has provided competitive advantages. The pilots felt comfortable ordering the plane, while the airlines did not have to invest in expensive training courses for their pilots and their mechanics. For Boeing, it was also faster and less expensive to redesign and certify this model than to do it entirely from scratch.

However, after two fatalities in less than five months, this strategy left the company in crisis. The Max forced the design of the 737 and created a plane equipped with a patched system that deprives pilots of some of the security features that can play an important role in a crisis, the same as those used for years. It's the only modern Boeing not to have an electronic alert system that explains what does not work and how to fix it. Instead, pilots must review a manual.

The Max also needed improvised solutions to keep the plane in the air, just like his predecessors, alternative methods that may have compromised security. Although the findings are not definitive, the researchers suspect that an alternative, a stall prevention system designed to compensate for larger engines, was crucial in last month's crash in Ethiopia and its predecessor in the US. Indonesia.

The Max is not your father's Buick, said Dennis Tajer, spokesperson for the American Airlines Pilots Union who has been flying the 737 for a decade. He added: "We do not ignore the fact that the base of this plane dates from the sixties."

The Max, the best selling Boeing model, with more than five thousand orders, suddenly threatens the reputation of the company. It may take weeks or months before regulators around the world stop vetting after Boeing 's expected software fix has been delayed. Southwest Airlines and American Airlines have canceled some flights from here May due to Max 's downtime.

The company suspended the production of the aircraft, which put pressure on its profits and some buyers reconsidered their orders. Shares of the company fell more than 4% on April 8 and 11% since the accident in Ethiopia.

"At the time, it was the most modern, but it was fifty years ago," said Rick Ludtke, an engineer who worked at Boeing and helped design the company. Max. "This is not a good plane for the current environment."

The 737 has long been a reliable aircraft, having flown for decades with relatively few problems. Boeing spokesman Gordon Johndroe defended the development of the Max and said the airlines wanted an updated 737 instead of a new one-aisle aircraft and that the pilots were involved in its design .

On January 17, 1967, at a factory near Seattle, flight attendants christened the first Boeing 737 and smashed sparkling bottles in his wing. Boeing announced that the plane was a smaller alternative to his larger plane, so they started naming him Boeing Baby.

Initially, sales were lower than those of Boeing's main competitor, McDonnell Douglas. In 1972, Boeing had only delivered 14 planes and planned to sell the program to a Japanese manufacturer, said Peter Morton, marketing director of the 737 in the early 1970s. "We had to decide if we were going to stop producing it or invest in it, "said Morton.

Boeing decided to invest. The 737 finally began to be sold, after airline deregulation in 1978. Six years later, Boeing updated the 737 with its series of "clbadics," followed by the "next generation" in 1997 and the Max 2017. In the United States, nearly one in three domestic flights are carried out in a 737, more than any other airline line.

Each of the three restructurings is accompanied by a new engine, cabin upgrades and other modifications. However, Boeing has avoided renewing the plane to rebadure the airlines, according to its current and former leaders, pilots and engineers, some of whom have requested anonymity due to open investigations. The airlines wanted the new 737s to be identical to their predecessors so that pilots would not have to undergo expensive flight simulator training and could easily adopt the new aircraft.

Boeing's strategy worked. The Federal Aviation Administration never needed simulator training for pilots moving from one 737 to another.

In 2011, Boeing's executives began to wonder if the design of the 737 had come to an end. The company wanted to create a brand new single-aisle aircraft. Then his rival Airbus, Boeing, added a new fuel efficient engine to his line of single – aisle aircraft, the A320, and Boeing quickly decided to modernize the aircraft.

"We all rolled our eyes thinking: here we are again, the 737," said Ludtke, the former 737 Max cabin engineer, who worked 19 years at Boeing.

"Maybe no one meant that it was not sure, but we really felt we had reached the limit," he added.

Some engineers were frustrated with having to spend years updating the same aircraft, making sure to limit the changes, instead of starting all over again and incorporating significant technological advances, engineers and pilots said, old and current. The Max almost always has the same original layout of the cab and the hydraulic system of cables and pulleys to control the plane, which is not used in modern designs. Integrated computers have the processing power of home computers of the nineties. A spokesman for Boeing said the aircraft had been designed with an appropriate level of technology to ensure its safety.

Engineers' changes sometimes caused chain effects in the way the device was managed, forcing Boeing to be creative. The company has added a new system that moves the wing plates in part to reduce the stresses on the aircraft due to its extra weight. Boeing recreated physical meters from decades ago on digital screens.

As Boeing put pressure on its engineers to find a way to implement larger engines with more efficient fuel consumption, weight was once again a problem. The simple extension of the landing gear to lift the plane could have broken the rules to get off the plane in case of emergency.

Instead, the engineers were able to add only a few inches to the front landing gear and later put the engines on the wing. The engines fitted, but the Max had a slightly erratic angle when he was parked.

Although the design solved one problem, it generated another one. The larger size and new location of the engines gives Max a tendency to tilt during certain flight maneuvers, potentially at a dangerous angle.

To compensate, Boeing engineers created the Maneuver Enhancement System (MCAS), an automated flight control software that would come down from the nose of the aircraft if it was too high. The software was designed to run in the background so Max could fly like his predecessor. Boeing did not mention the system in its training materials for the Max.

Boeing also designed the system so that it relies on a single sensor – which is extraordinary in aviation, where redundancy is common. Several engineers working at Boeing who did not participate directly in the design of the system stated that their colleagues had probably opted for this approach, as the use of two sensors could create other problems. If one of the two sensors fails, the system may have difficulty knowing which one is correct.

Max also lacked more modern security features.

Most new Boeing aircraft have electronic systems with which pilots can consult a pre-flight checklist, making sure not to skip any steps or neglect any parts that do not work well. . In the Max, pilots still complete these lists manually in a book.

A second electronic system on other Boeing aircraft also informs pilots of unusual or dangerous situations during the flight and displays the recommended actions to resolve them.

In the 737, a light usually indicates the problem and drivers should review their printed manuals to find the way forward. On the crashed Indonesian flight, while Lion Air pilots had problems with the MCAS to control the plane, they consulted the manual just before the plane collapsed. in the Java Sea, causing death. of the 189 people who were on board.

"While I fly the plane," said Tajer, the captain of American Airlines 737. "Instead of appearing on your screen, it says:" Here is the problem and the list of recommended measures "".

Boeing decided not to add this system to Max because it could have caused regulators to demand a new pilot training program, according to two former Boeing employees involved in the decision.

The Max also works with a complex network of cables and pulleys that, when pilots stretch the controls, transfer motion to the tail. In comparison, the most modern Airbus and Boeing aircraft, such as the 777 and 787, are "cable flights", which means that pilots' movements on flight controls are transmitted to a computer. who directs the plane. . The design allows for more automation, including systems preventing the jet from entering dangerous situations, such as flights that are too fast or too weak. Some 737 pilots said they preferred the cable and pulley system to the cable because they thought it gave them more control.

In recent accidents, the researchers felt that the MCAS had a malfunction that had displaced a drift, called a stabilizer, by tilting the aircraft to the ground. According to the preliminary report of accident, the pilots tried to fight the system during the unfortunate flight of Ethiopian Airlines, turning off the engine stabilizer.

Once the current was cut, the pilots attempted to regain control manually by turning a rudder near their seat. The 737 is the latest Boeing jet that uses a manual rudder as a backup system. But Boeing has known for a long time that it is difficult to turn the rudder at high speed and it is possible that the two riders had to work together.

According to the preliminary report of accident, the first officer said that the method did not work in the last moments of the flight of Ethiopian Airlines. About a minute and 49 seconds later, the plane crashed, killing 157 people.

Rebecca R. Ruiz and Stephen Grocer collaborated on this report. Kitty Bennett collaborated in the investigation.

* Copyright: c.2019 New York Times Press Service