​​Boeing on 11 November estimates deliveries of its 737 Max aircraft could resume in December as it announced the completion of the first of five milestones to gain approval of safety modifications from the US Federal Aviation Administration to return those aircraft to service.

Boeing says 737 Max deliveries could resume in December as it announced the completion of the first of five milestones to gain approval of safety modifications from the US Federal Aviation Administration to return those aircraft to service.

This estimate, however, is based on the airframer's assertion that the FAA could rescind the grounding of Max aircraft during the fourth quarter. The FAA reiterates that it will not commit to a timeline on when it will do so, and Boeing chairman David Calhoun has said it could take "at least a year" for airlines worldwide to return Max fleets to service even after the agency determines they are safe to fly.

The airframer states that the FAA and other regulators may approve "a phased approach" to return aircraft to service. European regulators have said January would be the earliest date they may certify 737 Max aircraft.

Resuming deliveries in December could reduce the waiting time carriers would face once the Max is cleared to return to service.

Locating storage space for Max jets is becoming a challenge as the grounded fleet grows. Boeing has reduced production of 737 Max aircraft since April but is still building around 40 aircraft per month, all of which must go into the airframer's finite parking spaces for aircraft.

This current rate of production is drying up predelivery payments for aircraft and placing pressure on Boeing, says Richard Aboulafia, civil aircraft analyst at the Teal Group in Virginia.

"They really need deliveries to resume so revenue can start coming in again," Aboulafia says.

Southwest Airlines and American Airlines both announced last week that they were extending Max flight cancellations into March, amid uncertainty of how long the groundings will last.

Boeing's optimism about gaining approval from FAA is newly bolstered by its announcement that the agency completed "a multi-day eCab simulator evaluation with the FAA to ensure the overall software system performs its intended function, both normally and in the presence of system failures".

The next steps will be a "simulator session with airline pilots to assess human factors and crew workload under various test conditions", followed by an FAA certification flight test, according to the airframer. Boeing would then have to submit its final Max aircraft software modifications to the FAA.

After that a Joint Operational Evaluation Board representing several regulatory agencies would conduct another multi-day simulator session with pilots to determine training requirements. The FAA Flight Standardization Board would then publish a report on the proposed training, review any public comments about it, and determine whether to approve the pilot training for Max aircraft.

Public opinion will likely be a key factor in whether airlines will be able to sell tickets on Max aircraft and some members of Congress have said they would not feel safe flying on the aircraft.

Both houses of Congress are investigating two fatal crashes of 737 Max aircraft in an effort to prevent future crashes and potentially reform FAA oversight. Lawmakers aim to hold Boeing accountable for mistakes that contributed to the crashes but have not yet expressed a desire to intervene in how airlines would return Max aircraft to service.