The Federal Aviation Administration said on Wednesday it does not have a specific timetable on when Boeing Co’s troubled 737 MAX jet would return to service after two fatal crashes led to the airplane’s worldwide grounding in March.

FAA spokesman Greg Martin said the agency has “no timetable” for allowing the 737 MAX to resume flying and will act “only when it is safe to return to service.”

Bloomberg reported earlier that the troubled 737 MAX aircraft will be back in the air by December, citing a top Federal Aviation Administration safety official.

Boeing did not immediately respond to a request for comment, and has not given a timeline on when the planes would be back in service.

Boeing is not expected to submit its formal software fix to the FAA this week or conduct a certification test flight that is required before it can submit the fix and training upgrade for approval, two people briefed on the matter told Reuters.

Grounded WestJet Boeing 737 Max aircraft are shown at the airline’s facilities in Calgary, May 7. WestJet’s schedule is adjusted through August 3 to accommodate the grounding and a spokesperson said Wednesday the airline was in close touch with regulators. (Jeff McIntosh/The Canadian Press)

A battered aviation industry has been speculating on when Boeing will win regulators’ approval to put the plane back in the air along with a batch of software upgrades and training.

A spokesperson for WestJet told CBC News that its schedule is adjusted through August 3. “We continue to monitor the situation and will adjust our schedule as required,” said Morgan Bell.

“WestJet remains closely in contact with our partners at Boeing, Transport Canada and other regulators to understand how and when to safely reintroduce the MAX aircraft into service.”

Air Canada spokesperson Peter Fitzpatrick said that because the timeline for the plane’s return to service is unknown, the airline has removed all 737 MAX aircraft from its schedule until at least September 2.

“Through various measures we have maintained enough capacity to operate 96 per cent of previous planned flights and customers can plan and book their travel with Air Canada with full confidence.”

American Airlines Group Inc. said on Sunday it was extending cancellations of about 115 daily flights into September due to the grounding.