The US  air transport regulator (FAA) has dashed  Boeing hopes that its 737 MAX will fly  again this year, before the authority submits to questions from Congress about its response to two fatal accidents.

In an interview prior to a hearing in Congress, the head of the Federal Aviation Administration (FAA), Steve Dickson, told CNBC that the plane will not be authorized to fly before 2020.

The process to approve the return of the MAX to the still has 10 or 11 milestones to complete, including a certification flight and a period of public comment on the pilot training requirements, Dickson said.

"If you do the calculations, it will run until 2020," he added.

The MAX has been grounded since March after the second of two accidents that killed a total of 346 people.

Boeing, which did not immediately respond to the AFP inquiry, was aiming to obtain regulatory approval this month and expected flights to resume in January.

Dickson said: "I have made it very clear that Boeing's plan is not the FAA's plan." He added: "We are going to keep our heads down and support the team so that this report is done well."

Boeing and the FAA have been under intense scrutiny after the accidents, for their response to problems with the aircraft, including an automatic flight management system involved in both cases.

Lawmakers put the magnifying glass on FAA officials, and wonder if there was a lax supervision of Boeing during the original certification of the aircraft.

The delay in allowing MAX to resume flights has led Boeing to reduce the production of its best-selling aircraft, while deliveries of new devices are suspended.

An article in The Wall Street Journal on Wednesday indicated that the FAA's analysis after the Lion Air plane crash in October 2018 estimated that unless arrangements were made to the key flight management system, the MAX was prone to 15 similar accidents during its useful life of decades, a higher rate than other airplanes.

A former FAA official quoted by the newspaper said the high rate would be "unacceptable" in the current security context. But instead of suspending the plane, the FAA determined that it would require Boeing to review the MCAS flight management system in a supervised process, among other measures that proved insufficient.