Boeing said Monday it now expects its grounded 737 Max to resume commercial service in January as it works to address questions from regulators over its documentation for revisions to the plane’s software.

Boeing said it is possible that resumption of Max deliveries to airline customers could begin in December and added it is working toward final validation of the updated training requirements “which must occur before the Max returns to commercial service, and which we now expect to begin in January.”

American Airlines and Southwest Airlines said Friday they were pushing back the resumption of flights because of the 737 Max grounding until early March.

Last week, Reuters reported that U.S. and European regulators had not been able to complete a software documentation audit in Cedar Rapids, Iowa of the 737 Max because of significant gaps and substandard documents. The U.S. Federal Aviation Administration (FAA) must complete that audit before a key certification test flight can be scheduled.

“We are taking the time to answer all of their questions,” Boeing said in a statement Monday, adding that it is aiming for “FAA certification of the Max flight control software updates during this quarter.”

Boeing also said that it has completed one of five milestones needed before the plane can return to service: a multi-day eCab simulator evaluation with the FAA to ensure the software system performs as intended even if there is a system failure.

On Friday, the FAA told U.S. lawmakers a preliminary review by a blue-ribbon panel has found Boeing’s design changes to a key safety system to be “safe” and compliant with regulations.