The Boeing 737 MAX is about ready to return to US skies. Will it make it for the holidays?

U.S. authorities are in the final miles of the 19-month marathon to re-certify the Boeing 737 MAX.

Most expect the Federal Aviation Administration to sign off on changes to the aircraft's systems and training protocols before the end of the year. Once this happens, the race will be on to see what U.S. airline will return the jet to service first.

“I like what I saw," FAA administrator Steve Dickson said in September after piloting a modified MAX 7 for 40 minutes above Washington state. At the time, he would not commit to a return-to-service timeline but did say regulators were in the "home stretch" of the process.

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American Airlines, Southwest Airlines and United Airlines flew a combined 72 MAXes when the aircraft was grounded in March 2019. The grounding occurred after two fatal crashes in Ethiopia and Indonesia took the lives of 346 people.

Now, the aircraft appears poised to resume service as regulators near closers to approving the jet to fly commercial flights again.

“Based on what we’re hearing, that would allow for an ungrounding sometime in the month of November," said Robert Isom, president of American, painting an optimistic view during a third quarter earnings call on Thursday. "If that holds true, that would allow us to be flying the aircraft [about] a month later.”

This timeline fits with what American is already selling. The airline has 737 MAX 8-operated flights for sale beginning Dec. 29 on the New York-Miami route — also the first route it flew with the plane when it first debuted for American in 2017.

Related: FAA chief upbeat after piloting Boeing 737 MAX test flight, but says ‘still work to do’

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American flew 24 MAX 8s when the jet was grounded in March 2019. It has orders for another 76 planes with plans to take delivery of as many as eight from Boeing this year. At least 10 more MAXes are scheduled for delivery to American in 2021.

Not every airline is as optimistic. Also speaking on Thursday, Southwest chief operating officer Mike Van de Ven only went as far as to say the carrier hoped re-certification would occur this year.

"Ultimately, an airworthiness directive and instructions need to be issued for an ungrounding," he said during the Dallas-based carrier's third quarter earnings call. "We’re hopeful that could be before the end of the year.”

Related: Southwest cuts Boeing MAX deliveries by 75 jets over next two years

Southwest will need three- to four-months to modify its MAX 8s and train pilots before it will resume flying the planes, Van de Ven said. This would push a re-introduction to as late as April if the MAX is re-certified in December.

The airline flew 34 737 MAX 8s when the jet was grounded. At the end of June, it had outstanding orders and commitments for another 380 MAXes with 48 aircraft due through the end of 2021.

United was even less committal on its MAX timeline during an earnings call on Oct.15. Commercial chief Andrew Nocella said the carrier does not know when the plane will be re-certified, but did not plan on resuming flights until 2021.

The Chicago-based carrier operated 14 737 MAX 9s when the plane was grounded. It has firm orders for 171 more MAXes.

Related: American delays MAX deliveries, retires Airbus A330s

In July, Boeing CEO Dave Calhoun said the planemaker hoped for a re-certification of the MAX in the fourth quarter.

The timeline of the MAX return will determine a number of other fleet decisions at U.S. airlines. Alaska Airlines is considering topping up its order for 32 MAXes to replace its Airbus A320s and Southwest is eyeing the MAX 7 as a replacement for its 737-700s.

“The MAX needs to be re-certified for that to be a viable plane," Ben Minicucci, president of Alaska Airlines, said when asked if an order to replace the A320s was imminent during the company's third quarter earnings call on Thursday. The airline has options for an additional 37 MAX jets on top of its firm order.

Reuters has reported that an Alaska order for more MAXes could occur shortly after FAA sign off.

Related: Why Alaska Airlines can’t retire its Airbus A320s all at once

Southwest has a lengthier timeline. The carrier aims to make a decision on either the Airbus A220 or MAX 7 to replace its 737-700s in the next year, said Van de Ven. Deliveries would begin around 2025.

A commitment for more MAXs from the world's largest 737 operator Southwest would be Boeing's to lose. However, since the grounding of the jet, the airline's management team has publicly acknowledged the benefit of two aircraft families for an airline its size — especially if one was grounded again.

Southwest still views the MAX 8 as the most efficient in its fleet despite the grounding. Once it resumes flying the plane, it plans to initially use it to replace the 737-700s that are due to exit its fleet in 2021.

Related: Southwest Airlines expands again, adds three more cities to its route map