WASHINGTON/SEATTLE (Reuters) - The head of the U.S. Federal Aviation Administration has told his team to “take whatever time is needed” in their review of Boeing Co’s 737 MAX, according to a Nov. 14 memo and video message reviewed by Reuters.

FILE PHOTO: An aerial photo shows Boeing 737 MAX aircraft at Boeing facilities at the Grant County International Airport in Moses Lake, Washington, September 16, 2019. REUTERS/Lindsey Wasson -/File Photo

The comments came days after Boeing said it expected the FAA to certify the 737 MAX, issue an airworthiness directive and unground the plane in mid-December. That timetable sent the planemaker’s stock price soaring on Monday, even as it acknowledged that it would not win approval for changes to pilot training until January.

U.S. officials have privately said this week that Boeing’s timetable was aggressive - if not unrealistic - and was not cleared in advance by regulators.

On Friday, FAA Administrator Steve Dickson sent a clear message that the agency would make the decision on its own timetable on whether to unground the plane that was involved in two fatal crashes in five months, killing 346 people in Indonesia and Ethiopia.

“This effort is not guided by a calendar or schedule,” Dickson wrote in the memo sent to Ali Bahrami, a top FAA safety official.

Dickson offered his unequivocal support for a “data-driven methodical analysis, review and validation of the modified flight control systems and pilot training required to safely return the MAX to commercial service.”

Boeing still must complete an audit of its software documentation before it can schedule a key certification test flight and faces other hurdles.

In a video message posted on YouTube here&feature=youtu.be on Friday, Dickson said: "I am not going to sign off on this aircraft until I fly it myself and I am satisfied that I would put my own family on it without a second thought."

“I know there is a lot of pressure to return this aircraft to service quickly. But I want you to know, that I want you to take the time you need and focus solely on safety. I’ve got your back,” Dickson said. “The FAA fully controls the approval process.”

Boeing said on Friday it was working closely with the FAA and other regulatory authorities.

“With the rigorous scrutiny being applied, we are confident the MAX will be one of the safest airplanes ever to fly,” the company added, noting the “FAA and other regulatory authorities will determine the timing of certification and return to commercial service.”

The three U.S. airlines that operate the 737 MAX - Southwest Airlines Co, American Airlines Group Inc and United Airlines Holdings Inc - are scheduling flights without the aircraft until early March 2020, nearly a year since the grounding.

Separately, Representative Peter DeFazio, who heads the U.S. House Transportation and Infrastructure Committee, said on Friday he had sent a series of follow-up questions to Boeing Chief Executive Dennis Muilenburg about the decisions that were made before, during, and after the rollout of the 737 MAX.

Muilenburg testified before the committee on Oct. 30, and was repeatedly hammered by lawmakers over his compensation and key mistakes in the development of the MAX.