SEATTLE — In the days after the first crash of Boeing’s 737 Max, engineers at the Federal Aviation Administration came to a troubling realization: They didn’t fully understand the automated system that helped send the plane into a nose-dive, killing everyone on board.

Engineers at the agency scoured their files for information about the system designed to help avoid stalls. They didn’t find much. Regulators had never independently assessed the risks of the dangerous software known as MCAS when they approved the plane in 2017.

More than a dozen current and former employees at the FAA and Boeing who spoke with The New York Times described a broken regulatory process that effectively neutered the oversight authority of the agency.

The regulator had been passing off routine tasks to manufacturers for years, with the goal of freeing up specialists to focus on the most important safety concerns. But on the Max, the regulator handed nearly complete control to Boeing, leaving some key agency officials in the dark about important systems like MCAS, according to the current and former employees.

While the agency’s flawed oversight of the Boeing 737 Max has attracted much scrutiny since the first crash in October and a second one in March, a Times investigation revealed previously unreported details about weaknesses in the regulatory process that compromised the safety of the plane.

FAA-certified ‘safe’

The company performed its own assessments of the system, which were not stress-tested by the regulator. Turnover at the agency left two relatively inexperienced engineers overseeing Boeing’s early work on the system.

The FAA eventually handed over responsibility for approval of MCAS to the manufacturer. After that, Boeing didn’t have to share the details of the system with the two agency engineers.

Late in the development of the Max, Boeing decided to expand the use of MCAS. The new, riskier version relied on a single sensor and could push down the nose of the plane by a much larger amount.

Boeing did not submit a formal review of MCAS after the overhaul. It wasn’t required by FAA rules.

The agency ultimately certified the jet as safe, required little training for pilots and allowed the plane to keep flying until a second deadly Max crash, less than five months after the first.

The FAA and Boeing have defended the plane’s certification, saying they followed procedures.

“The 737 Max certification program involved 110,000 hours of work on the part of FAA personnel, including flying or supporting 297 test flights,” the agency said.

Boeing said that “the 737 Max met the FAA’s stringent standards and requirements as it was certified through the FAA’s processes.”

Boeing needed the approval process on the Max to go swiftly. Months behind its rival Airbus, the company was racing to finish the plane.

The regulator’s hands-off approach was pivotal. At crucial moments in the Max’s development, the agency operated in the background, mainly monitoring Boeing’s progress and checking paperwork. The nation’s largest aerospace manufacturer, Boeing was treated as a client, with FAA officials making decisions based on the company’s deadlines and budget.

During the Max certification, senior FAA leaders sometimes overruled their own staff members’ recommendations after Boeing pushed back.

After the crash of the Lion Air plane in October, FAA engineers were shocked to discover they didn’t have a complete analysis of MCAS. The safety review in their files didn’t mention that the system could aggressively push down the nose of the plane and trigger repeatedly, making it difficult to regain control of the aircraft.

Despite their hazy understanding of the system, FAA officials decided against grounding the 737 Max. Instead, they published a notice reminding pilots of existing emergency procedures.

The notice didn’t describe how MCAS worked. At the last minute, an FAA manager told agency engineers to remove the only mention of the system, according to internal agency documents.

The FAA department that oversaw the Max development had such a singular focus that it was named the Boeing Aviation Safety Oversight Office.

Many FAA veterans came to see the department as a symbol of the agency’s close relationship with the manufacturer. The top official in Seattle at the time, Ali Bahrami, had a tough time persuading employees to join, according to three current and former employees.

Some engineers believed Bahrami had installed managers in the office who would defer to Boeing. “He didn’t put enough checks and balances in the system,” Mike McRae, a former FAA engineer, said of Bahrami. “He really wanted abdication. He didn’t want delegation.”

The FAA said in a statement that Bahrami “dedicated his career to the advancement of aviation safety in both the private and public sectors.”

For decades, the FAA relied on engineers inside Boeing to help certify aircraft. But after intense lobbying by industry, the agency adopted rules in 2005 that would give manufacturers like Boeing even more control. By 2018, the FAA was letting the company certify 96% of its own work, according to an agency official.

In the middle of the Max’s development, two seasoned engineers in the FAA’s Boeing office left. The engineers, who had a combined 50 years of experience, grew frustrated with the work, which they saw as mostly paper pushing, according to two people with knowledge of the staff changes.

In their place, the FAA appointed an engineer who had little experience in flight controls, and a new hire who had gotten his master’s degree three years earlier. People who worked with the two engineers said they seemed ill-equipped to identify any problems in a complex system like MCAS.

Boeing played down the importance of MCAS from the outset. An early review by the company didn’t consider the system risky, and it didn’t prompt additional scrutiny from the FAA engineers, according to two agency officials. The review described a system that would activate only in rare situations.

The FAA engineers who had been overseeing MCAS never received another safety assessment. As Boeing raced to finish the Max in 2016, agency managers gave the company the power to approve a batch of safety assessments. They believed the issues were low risk.

Boeing was in the middle of overhauling MCAS. To help pilots control the plane and avoid a stall, the company allowed MCAS to trigger at low speeds, rather than just at high speeds. The overhauled version would move the stabilizer by as much as 2.5 degrees each time it triggered, significantly pushing down the nose of the plane. The earlier version moved the stabilizer 0.6 degrees.

When company engineers analyzed the change, they figured the system had not become any riskier, according to two people familiar with Boeing’s discussions on the matter. They assumed pilots would respond to a malfunction quickly, bringing the nose of the plane back up. In their view, any problems would be less dangerous at low speeds.