American Airlines has removed another month of Boeing 737 Max flights from its schedules and now plans for the aircraft to be back in service on 4 December.

The Fort Worth-based airline previously had Max flights resuming on 3 November.

american airlines Boeing 737 Max

The shift, which follows similar changes by Southwest Airlines and United Airlines, reflects American's latest estimate of when regulators will clear the aircraft to fly.

However, the actual timeline remains highly uncertain. Though Boeing still says it anticipates the Max will be airborne early in the fourth quarter, recent developments have highlighted work still uncomplete.

On 30 August, the Federal Aviation Administration confirmed that a multi-national safety panel reviewing the 737 Max's certification and flight control software needs additional time to complete its review.

The FAA now expects the Joint Authorities Technical Review panel will submit its findings "in the coming weeks". The agency has said its certification work is separate from the panel's review.

When convening the panel in April, the FAA said the group would likely complete its work in 90 days.

Additionally, on 1 September The Wall Street Journal reported the certification could be delayed several more weeks. The report says that in August a group of international regulators found Boeing failed to provide adequate details about changes made to the Max's flight computers.

Those regulators have asked Boeing to resubmit documents, says the report.

Still, American expresses confidence in its new 3 December return-to-service date.

"American Airlines remains confident that impending software updates to the Boeing 737 Max, along with the new training elements Boeing is developing in coordination with our union partners, will lead to recertification of the aircraft this year," the airline says in a statement.

American's schedule adjustment results in about 140 daily flight cancellations, which equates to 4,200 additional cancelled flights between 2 November and 2 December.

Last week, United adjusted its schedule, removing Max flights until 19 December.

Southwest has taken a more-conservative approach, removing the type from its schedules until 6 January.