Weeks after the first fatal crash of the 737 Max, pilots from American Airlines pressed Boeing executives to work urgently on a fix. In a closed-door meeting, they even argued that Boeing should push the authorities to take an emergency measure that would very likely result in the grounding of the Max.

The Boeing executives resisted. They did not want to rush out a fix, and said they expected pilots to be able to handle problems.

Mike Sinnett, a vice president at Boeing, acknowledged that the manufacturer was assessing potential design flaws with the plane, including new anti-stall software. But he baulked at taking a more aggressive approach, saying it was not yet clear that the new system was to blame for the Lion Air crash, which killed 189 people.

“No one has yet to conclude that the sole cause of this was this function on the airplane,” Mr Sinnett said, according to a recording of the 27 November meeting reviewed by The New York Times.

Less than four months later, an Ethiopian Airlines flight crashed, killing all 157 people on board. The flawed anti-stall system played a role in both disasters.

Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures Show all 9 1 /9 Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures This picture taken on March 11, 2019, shows debris of the crashed airplane of Ethiopia Airlines, near Bishoftu, a town some 60 kilometres southeast of Addis Ababa, Ethiopia. - An Ethiopian Airlines Boeing 737 crashed on March 10 morning en route from Addis Ababa to Nairobi with 149 passengers and eight crew believed to be on board, Ethiopian Airlines said. (Photo by Michael TEWELDE / AFP)MICHAEL TEWELDE/AFP/Getty Images AFP/Getty Images Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures Family members mourn the victims at the crash site of the Ethiopian Airlines operated Boeing 737 MAX aircraft, at Hama Quntushele village in the Oromia region, on March 13, 2019. - A Nairobi-bound Ethiopian Airlines Boeing crashed minutes after takeoff from Addis Ababa on March 10, 2019, killing all eight crew and 149 passengers on board, including tourists, business travellers, and "at least a dozen" UN staff. Families of the victims were taken to the remote site on March 13, 2019, where the plane smashed into a field with 157 passengers and crew from 35 countries, leaving a deep black crater and tiny scraps of debris. (Photo by TONY KARUMBA / AFP)TONY KARUMBA/AFP/Getty Images AFP/Getty Images Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures A page of a Boeing flight crew operations manual is seen at the scene of the Ethiopian Airlines Flight ET 302 plane crash, near the town of Bishoftu, near Addis Ababa, Ethiopia March 12, 2019. REUTERS/Baz Ratner REUTERS Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures epa07434278 Rescue workers search the site for pieces of the wreckage of an Ethiopia Airlines Boeing 737 Max 8 aircraft near Bishoftu, Ethiopia, 13 March 2019. Ethiopian Airlines flight ET 302 carrying 149 passengers and 8 crew was en route to Nairobi, Kenya, when it crashed on 10 March 2019 by yet undetermined reason. All passengers and crew aboard died in the crash. The Boeing 737 Max 8 aircraft has come under scrutiny after similar deadly crashes in Ethiopia and Indonesia within a few months. Several countries have banned the plane type from their airspace and many airlines have grounded their 737 Max 8 planes for safety concerns after the Ethiopian Airlines plane crashed minutes after take-off on 10 March. EPA/STRINGER EPA Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures A grounded Boeing 737 MAX 8 passenger plane of the Norwegian low-cost airline Norwegian is parked at the tarmac at Vantaa airport in Vantaa near Helsinki, Finland on March 13, 2019. - A number of countries have banned Boeing's 737 MAX 8 medium-haul workhorse jet from their airspace in response to the Ethiopian Airlines crash that killed all 157 people on board. (Photo by Heikki Saukkomaa / Lehtikuva / AFP) / Finland OUTHEIKKI SAUKKOMAA/AFP/Getty Images AFP/Getty Images Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures Rescue workers search the site for pieces of the wreckage of an Ethiopia Airlines Boeing 737 MAX 8 aircraft near Bishoftu, Ethiopia, 13 March 2019. Ethiopian Airlines flight ET 302 carrying 149 passengers and 8 crew was en route to Nairobi, Kenya, when it crashed on 10 March 2019 by yet undetermined reason. All passengers and crew aboard died in the crash. The Boeing 737 Max 8 aircraft has come under scrutiny after similar deadly crashes in Ethiopia and Indonesia within a few months. Several countries have banned the plane type from their airspace and many airlines have grounded their 737 Max 8 planes for safety concerns after the Ethiopian Airlines plane crashed minutes after take-off on 10 March. EPA/STRINGER EPA Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures A heap of debris from the wreckage of an Ethiopia Airlines Boeing 737 MAX 8 aircraft are piled at the crash site near Bishoftu, Ethiopia, 13 March 2019. Ethiopian Airlines flight ET 302 carrying 149 passengers and 8 crew was en route to Nairobi, Kenya, when it crashed on 10 March 2019 by yet undetermined reason. All passengers and crew aboard died in the crash. The Boeing 737 Max 8 aircraft has come under scrutiny after similar deadly crashes in Ethiopia and Indonesia within a few months. Several countries have banned the plane type from their airspace and many airlines have grounded their 737 Max 8 planes for safety concerns after the Ethiopian Airlines plane crashed minutes after take-off on 10 March. EPA/STR EPA Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures A crew working with an investigative team to clear the site after the Sunday crash of the Ethiopian Airlines operated Boeing 737 MAX aircraft, carry debris at Hama Quntushele village in the Oromia region, on March 13, 2019. - A Nairobi-bound Ethiopian Airlines Boeing crashed minutes after takeoff from Addis Ababa on March 10, killing all eight crew and 149 passengers on board, including tourists, business travellers, and "at least a dozen" UN staff. Families of the victims were taken to the remote site on March 13, 2019, where the plane smashed into a field with 157 passengers and crew from 35 countries, leaving a deep black crater and tiny scraps of debris. (Photo by TONY KARUMBA / AFP)TONY KARUMBA/AFP/Getty Images AFP/Getty Images Boeing 737 MAX grounding: Ethiopia Airlines Flight 302 in pictures FILE PHOTO: An American Airlines Boeing 737 MAX 8, on a flight from Miami to New York City, comes in for landing at LaGuardia Airport in New York, U.S., March 12, 2019. REUTERS/Shannon Stapleton/File Photo REUTERS

Boeing is facing intense scrutiny for the design and certification of the Max, as well as for its response to the two crashes. There are multiple investigations into the development of the Max. In recent days, unions representing pilots from American Airlines and Southwest Airlines have received federal grand jury subpoenas for any documents related to Boeing’s communications about the jet, according to three people with knowledge of the matter.

The Federal Aviation Administration is also under fire for its role in approving the Max, and its decision to wait for days after the second crash to ground the plane. At a congressional hearing this week, lawmakers will grill federal regulators about how the Max was certified.

Boeing declined to comment on the November meeting.

“We are focused on working with pilots, airlines and global regulators to certify the updates on the Max and provide additional training and education to safely return the planes to flight,” the company said in a statement.

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American Airlines said in a statement that it was “confident that the impending software updates, along with the new training elements Boeing is developing for the Max, will lead to recertification of the aircraft soon.”

The hour-long November meeting, inside a windowless conference room at the Fort Worth headquarters of the American Airlines pilots’ union, was confrontational at times. At the table was Mr Sinnett, along with Craig Bomben, a top Boeing test pilot, and one of the company’s senior lobbyists, John Moloney. They faced several union leaders, many of them angry at the company.

Michael Michaelis, an American pilot, argued that Boeing should push the FAA to issue what is known as an emergency airworthiness directive.

The FAA had already issued one directive after the Lion Air crash, instructing airlines to revise their flight manuals to include information on how to respond to a malfunction of the anti-stall system known as MCAS. But Mr Michaelis pushed Boeing to consider calling for an additional one to update the software.

Such a procedure would have required Boeing and airlines in the United States to take immediate action to ensure the safety of the Max, and would have likely taken the jet out of service temporarily.

“My question to you, as Boeing, is why wouldn’t you say this is the smartest thing to do?” Mr Michaelis said. “Say we’re going to do everything we can to protect that travelling public in accordance with what our pilots unions are telling us.”

Mr Sinnett did not budge, saying that it remained unclear that the new software, which automatically pushes the plane’s nose down, was responsible for the Lion Air crash. He added that he felt confident that pilots had adequate training to deal with a problem, especially now that pilots — who were not initially informed about the new system — were aware of it.

“You’ve got to understand that our commitment to safety is as great as yours,” Mr Sinnett said in the meeting. “The worst thing that can ever happen is a tragedy like this, and the even worse thing would be another one.”

The pilots expressed frustration that Boeing did not inform them about the new software on the plane until after the Lion Air crash.

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“These guys didn’t even know the damn system was on the airplane, nor did anybody else,” said Mr Michaelis, the union’s head of safety.

Another American pilot, Todd Wissing, expressed frustration that no mention of the system had been included in the training manual for the 737 Max.

“I would think that there would be a priority of putting explanations of things that could kill you,” Mr Wissing said.

The Boeing executives, Mr Sinnett and Mr Bomben, explained that the company did not believe that pilots needed to know about the software, because they were already trained to deal with scenarios like the one on the doomed Lion Air flight. All pilots are expected to know how to take control of an aircraft when the plane’s tail begins moving in an uncontrolled way because of a malfunction, nudging the aircraft towards the ground.

“The assumption is that the flight crews have been trained,” Mr Sinnett said in the meeting. He added later: “Rightly or wrongly, that was the design criteria and that’s how the airplane was certified with the system and pilot working together.”

When the pilots pressed Boeing to consider encouraging the FAA to issue an emergency airworthiness directive, Mr Sinnett made the case against moving too quickly.

“We don’t want to rush and do a crappy job of fixing the right things and we also don’t want to fix the wrong things,” Mr Sinnett said, later adding, “For flight-critical software, I don’t think you want us to rush, rush it faster.”

Mr Sinnett acknowledged that the company was looking into potential mistakes in the design of the jet.

“One of the questions will be, is our design assumption wrong?” Mr Sinnett said. “We’re going through that whole thought process of, were our assumptions really even valid when we did this?”

But he remained steadfast that pilots should know how to handle a malfunction of the new software on the plane, given their existing training.

As the meeting was concluding, Dennis Tajer, spokesman for the union, asked the Boeing executives whether they were still confident in the Max.

“Do you feel comfortable that the situation is under control today, before any software fix is implemented?” he asked.

Mr Sinnett replied immediately: “Absolutely.”