CHICAGO — In a tense and steely news conference, his first since two deadly crashes of 737 MAX airplanes, Boeing Chairman and CEO Dennis Muilenburg faced sharp questioning but refused to admit flaws in the design of the airplane’s systems.

“We have gone back and confirmed again, as we do the safety analysis, the engineering analysis, that we followed exactly the steps in our design and certification processes that consistently produce safe airplanes,” he said. “It was designed per our standards. It was certified per our standards.”

In the case of the MAX, those processes certified as safe a new flight-control system that was triggered on both the Lion Air and Ethiopian crash flights by a single faulty sensor and then engaged repeatedly to push the nose of each airplane down. Boeing is currently flight testing a software redesign of this system — Maneuvering Characteristics Augmentation System (MCAS).

Yet Muilenburg would not concede that there was anything wrong with the original MCAS design, saying only that the system is being “improved” with the software redesign.

He said airplane accidents are typically due to “a chain of events,” and that “it’s not correct to attribute that to any single item.”

He pointed to actions by the pilots on the two flights, who he said did not completely follow the standard procedure when uncommanded tail movements begin to push the jet’s nose down. He added that Boeing’s system safety analysis of MCAS, a technical document prepared by Boeing during certification of the MAX, depends in part on the pilot making the appropriate response in the case of a system failure.

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At the brief news conference following Boeing’s annual shareholder meeting at Chicago’s Field Museum, Muilenburg faced one question after another about flaws in MCAS but repeatedly declined to concede that it was badly designed.

His statements hewed closely to the line he followed on an earnings teleconference last Wednesday, when he said the MAX crashes were not due to any “technical slip” by Boeing during the jet’s design or certification.

He took questions for less than 15 minutes. Finally, after parrying a question about whether he had thought about resigning and a last question about blame for MCAS, Muilenburg walked out grim-faced.

As he strode briskly from the room, many reporters had not been called upon. One of those shouted after him: “346 people died. Can you answer some questions?”

Boeing’s proposed software fix for MCAS ensures the system takes input from two sensors, instead of one. It will activate only once, not multiple times, if the sensor reading remains stuck at a high value. And the power of the system will be limited, so that the pilot can always pull back on the control column with enough force to counteract any automatic nose-down movement.

With that fix, Muilenburg said, the MAX when it returns to service will be “one of the safest airplanes ever to fly.”

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During the shareholder meeting, a couple of small stockholders asked more gently worded questions about the MAX crashes.

One older man, who identified himself as an engineer, questioned how MCAS was designed to depend on a single unreliable sensor. A young woman questioned whether oversight by the Federal Aviation Administration was sufficiently independent.

Muilenburg’s response to the engineer simply reiterated the statement that Boeing had followed its long-standing procedures in the design and development of the MAX.

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On the need for independent oversight, he said Boeing’s airplane development process includes “non-advocate reviews,” when experts who aren’t on the specific program are brought in to evaluate it.

Security was tight at the shareholder meeting, which was attended by the entire Boeing board. Attendees were screened through airport-style metal detectors and explosives-detecting dogs sniffed at all bags.

The event featured shareholder votes on a series of formal proposals, including one to separate Muilenburg’s dual role as chairman and CEO by appointing a separate chairman, another seeking to ensure that executive pay is not boosted by share repurchases, and another to force more disclosure of Boeing’s lobbying activities.

All these external proposals were given short shrift by the board and none came close to passing.

Outside the museum, a small band of relatives of people who died on the Ethiopian Airlines plane protested in the pouring rain. One sign called for the prosecution of Boeing and its executives for manslaughter.

Tarek Milleron, the uncle of 23-year-old Samya Stumo, who was among those killed, said that Boeing’s leadership “should open up on the chain of events that led to these accidents.”

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