Why hasn't the FAA cleared the Max? Here's the worry

One big question hanging over Boeing and the 737 Max: When will it return to service?

The head of the Federal Aviation Administration is set to testify before a House committee on Wednesday. World safety agencies, airlines and the traveling public will be listening for clues.

The Max was grounded last March. Early in the grounding, attention focused on the Maneuvering Characteristics Augmentation System (MCAS) and its role in repeatedly pushing the Max's nose down. Two crews were overpowered by MCAS and the crashes killed 346 people.

Back in the spring it was widely reported that Boeing was finalizing a fix for MCAS. And yet the plane remains uncertified.

“I have been curious how it could be the case that in April, Boeing announced in just a few weeks we have the fix it’ll be delivered to the FAA in a few weeks," said Stan Sorscher, a former Boeing engineer and official at the engineers' union SPEEA. “That assurance is repeated and repeated and repeated and we never quite find out what is holding up the certification."

Boeing says it is doing everything it can to end the grounding. However, aviation safety consultant Alan Diehl recently said on MSNBC that it could still be months.

"I would not expect this airworthiness directive to be issued at least for another couple, three months,” he said. "I’m convinced the FAA wants a buy-in from their counterparts in Europe, Canada and around the world."

That may be hard to do. Last month a Canadian safety official wrote to his counterparts saying he still had concerns about MCAS. He said new issues were “constantly appearing” with the latest version. His suggestion: Take it out and certify the Max as a new airplane.

It’s not clear how widely held this view is, but Sorscher said it makes some sense.

“There is a certain elegance to letting the plane fly the way it was designed. And I think that’s what he was getting at," he said. "It comes with a little more complexity in how you certify the airplane.”

It would also take more months to conduct a broader certification.

Michel Merluzeau, of the aerospace analysis company AIR, says Boeing may not have that kind of time.

“Anything that goes too deep into 2020 — and I mean beyond March, beyond April — we would be entering uncharted territory and that could lead to a more serious crisis at the Boeing level and for the Puget Sound area as a whole," Merluzeau said.

About 9,000 people depend on the 737 line in Renton for jobs. However, the trust of the traveling public depends on confidence in the FAA’s decision.

Merluzeau said FAA chief Steve Dickson understands all of that.

"He’s going to do what he needs to do to restrengthen the perception of the FAA as the premiere regulator agency in the world. And that’s what we need. We need a strong FAA," he said.