June 16 (UPI) -- Boeing CEO Dennis Muilenburg said Sunday there is still no clear schedule for when the company's 737 Max planes will be cleared to fly again and acknowledged communications about the plane with regulators and the airlines were "unacceptable."
Speaking to reporters ahead of the Paris air show, Muilenburg said the company would work to ensure the plane is safe, including planned Federal Aviation Administration flight trials of its safety improvements, after the planes were grounded globally as the model was involved in two crashes that killed 346 people.
"We haven't given the airlines a specific timetable," Muilenburg said. "This will all be governed by safety."
Last week, American Airlines extended its cancellations of flights involving the 737 Max through Sept. 3 and other U.S. airlines including Southwest and United have also canceled flights involving the plan through August.
The Wall Street Journal reported that FAA flight tests could begin as early as next week and could last about a week followed by several weeks of analyzing and documenting the results, but a spokesman told the outlet the agency had "no updates to provide at this time."
"We continue to work with Boeing to gather the necessary data we need to ensure the aircraft is safe to return to service," the spokesman said.
Muilenburg also noted that "it will take time rebuilding the confidence of our customers and the flying public," when the plane is cleared to fly again.
He added that it was "unacceptable" that the company's communication wasn't consistent in the aftermath of the crashes and pledged the company would work to resolve issues that led to flaws in the plane's software and sensors going undiscovered.
"Clearly, we can make improvements and we understand that and we will make those improvements," said Muilenburg.
And Muilenburg said he was "disappointed" the company didn't reveal sooner a discovery by engineers in 2017 that cockpit alerts of certain sensor malfunctions had problems because of a software error. Senior Boeing leaders said they didn't know about the issue until after the second crash.