PARIS—The chief executive of Boeing said the company made a “mistake” in handling a problematic cockpit warning system in its 737 Max jets before two crashes of the top-selling plane killed 346 people, and he promised transparency as the U.S. aircraft maker tries to get the grounded model back in flight.

Boeing CEO Dennis Muilenburg told reporters in Paris that Boeing’s communication with regulators, customers and the public “was not consistent. And that’s unacceptable.”

The U.S. Federal Aviation Administration has faulted Boeing for not telling regulators for more than year that a safety indicator in the Max cockpit didn’t work.

Pilots are angry the company didn’t tell them about the new software that’s been implicated in the crashes in Indonesia and Ethiopia.

“We clearly had a mistake in the implementation of the alert,” Muilenburg said.

He expressed confidence that the Boeing 737 Max would be cleared to fly again later this year. The model has been grounded worldwide for three months, and regulators need to approve Boeing’s long-awaited fix to the software.

Muilenburg called the crashes of the Lion Air and Ethiopian Airlines jets a “defining moment” for Boeing, but said he thinks the result will be a “better and stronger company.”

Speaking ahead of the Paris Air Show, Muilenburg said Boeing is facing the event with “humility” and focused on rebuilding trust.

In the United States, Boeing has faced scrutiny from members of Congress and the FAA over how it reported the problem involving a cockpit warning light.

The company discovered in 2017 that a warning light designed to alert pilots when sensors measuring the angle of a plane’s nose might be wrong only worked if airlines had purchased a separate feature.

The angle-measuring sensors have been implicated in the Lion Air crash in Indonesia and the Ethiopian Airlines crash in March. The sensors malfunctioned, alerting software to push the noses of the planes down. The pilots were unable to take back control of the planes.

Boeing told the FAA of what it learned in 2017 after the Indonesia crash in October. Boeing and the FAA have said the warning light wasn’t critical for flight safety.

Muilenburg forecast a limited number of orders at the Paris show, the first major air show since the crashes, but said it was important to attend to talk to customers and others in the industry.

He also announced that Boeing is raising its long-term forecast for global plane demand, notably amid sustained growth in Asia.