The head of the U.S. Federal Aviation Administration (FAA) said on Tuesday Boeing must improve its safety culture and address quality issues before the agency will allow the plane maker to boost 737 MAX production.

Mike Whitaker, the FAA Administrator said that the agency has not yet begun discussions with Boeing about hiking 737 production, and the FAA will only permit an increase when Boeing is "running a quality system safely."

Whitaker said he has the tools to hold Boeing "accountable and fully intend to use them," adding that Boeing is allowed to produce 38 of the 737 planes per month, but actual current production "is lower than that."

The U.S. FAA in late January took the unprecedented step of telling Boeing it would not allow the company to expand 737 MAX production in the wake of a mid-air emergency on an Alaska Airlines jet earlier in the month. 

Boeing's chief financial officer, Brian West, said last month that the plane maker's first-half output of 737 planes would be less than 38 per month, but in the second half, he said he expected it would "move toward that 38 per month, but it will be dictated" by the FAA.

Whitaker said the timeline on when Boeing will be allowed to boost the 737 MAX production rate will depend on "how effectively they can implement these changes in the safety culture and bring their quality levels up to where they need to be."

The U.S. Justice Department has opened a criminal probe into the January mid-air 737 MAX 9 cabin panel blowout. 

On February 28, Whitaker said Boeing must develop a comprehensive plan to address "systemic quality-control issues" within 90 days and set milestones. "This is a long-term endeavor; it takes a long time to change culture," Whitaker said on Tuesday, adding that "they certainly have it within their capabilities to do that. I don't want to give the impression that this is a 90-day fix, and then we move on." 

Separately, Whitaker spoke with United Airlines CEO Scott Kirby over the weekend about a series of recent safety incidents, including a plane that lost a panel on Friday. Kirby told customers on Monday that the airline is reviewing recent safety incidents and using insights to update employee safety training and procedures.

(With input from Reuters)