The Boeing 737 Max is flying passengers again in the US - here's when and where each US airline will be flying it

• US airlines are gearing up to relaunch the Boeing 737 Max back into service following its ungrounding by the Federal Aviation Administration.
• American Airlines flew the first passenger flight on Tuesday while United Airlines, Southwest Airlines, and Alaska Airlines will all fly the Max in 2021.
• All except for Southwest Airlines have scheduled the first routes for the Max with cities including Miami, New York, Houston, Seattle, Los Angeles, and Denver among the first on the list.

After a 20-month grounding by the Federal Aviation Administration in the US, the Boeing 737 Max is finally flying passengers again in the US.

American Airlines flew the first scheduled flight on Tuesday from Miami to New York, inaugurating a new chapter for the airliner slowly but surely. The new year will see a gradual ramp-up of operations by the four carriers that currently fly variants of the 737 Max or plan to take delivery of their first models in 2021 including American, Southwest Airlines, United Airlines, and Alaska Airlines.

Just 72 Boeing 737 Max aircraft were flying in the US before the March 2019 grounding, Cirium data shows, but Boeing didn't immediately stop building them, leaving many completed aircraft sitting idle. By the end of 2021, the Max will likely become more commonplace at airports across the US as airlines rush to get the planes back in the skies to take advantage of their economic benefits and put the grounding behind them.

Read more: American will lose its crown as the biggest US airline and could fall behind Delta and United as it struggles to pay off $38 billion in debt

To the north, Canadian carriers WestJet and Air Canada will also resume Max flying once the country's aviation regulator, Transport Canada, clears the jet for passenger service. Authorization is expected to be "imminent," as The Canadian Press reported in early December, and both carriers flew the Max to cities across the US before its grounding, though Canada remains largely closed to Americans due to the pandemic.

Brazil's Gol Linhas Aéreas began flying the Max on December 9, the earliest of any airline, on domestic routes from Sao Paulo. Aeromexico soon followed on December 21, flying the jet between Mexico City and Cancun.

Here's where the Boeing 737 Max will be flying in the US as it returns to the skies.

American Airlines

American's first Max flight on Tuesday was largely uneventful, and that's great news when it comes to the Max.

Miami will now see additional Max routes come January with American recently adding seven cities to the aircraft's destination list, Cirium data shows. Max service will quickly be expanding in the new year to Boston; Washington, DC; Orlando, Florida; Tampa, Florida; San Juan, Puerto Rico; St. Thomas, US Virgin Islands; and St. Croix, US Virgin Islands, as well as New York's John F. Kennedy International Airport, throughout January.

In February, the jet is scheduled to serve Latin America and foreign countries in the Caribbean including Costa Rica, Dominican Republic, El Salvador, Mexico, Haiti, Nicaragua, Jamaica, Cuba, Guatemala, Aruba, Antigua, and Brazil. The Miami-Phoenix route will also see the aircraft.

American plans to have 34 Boeing 737 Max 8 aircraft by year's end, president Robert Isom told reporters before the first flight, with another 66 on order with Boeing. In early December, employees of the airline and members of the media, including Business Insider's David Slotnick, were invited for demonstration flights onboard the aircraft in a push to shore up confidence in the jet ahead of its second commercial debut.

United Airlines

United has a scheduled return to service date for the Max of February 11, 2021, with the jets slated to fly routes from Houston and Denver. The full slate of routes will be announced on January 6, 2021, when United updates its February flying schedule.

Some routes for which United used the aircraft before the March 2019 grounding included Houston-Anchorage, Los Angeles-Honolulu, and San Francisco-Orlando. The aircraft was primarily based in Los Angeles, Houston, and San Francisco, with a penchant for serving the longer routes in United's domestic network, including to the Hawaiian Islands.

United currently has 14 Boeing 737 Max 9 aircraft in its fleet, which it began flying before the March 2019 grounding, and also has orders for the larger 737 Max 10, Cirium data shows.

Alaska Airlines

Alaska has a scheduled start date of March 1, 2021, Cirium data shows, for its long-delayed Boeing 737 Max operations, flying first from Seattle; Los Angeles; San Diego, and Portland, Oregon, Cirium data shows, but that's subject to change.

The first routes include Seattle-Los Angeles, Seattle-San Diego, Los Angeles-Portland, Oregon.

No other Max routes are currently loaded in Alaska's schedule, according to Cirium, but it's expected that the Max will fly Alaska's routes to Hawaii and transcontinental routes as that's where the cost savings will be the most pronounced.

Before it flies passengers, Alaska says it will perform proving flights on the routes the jet is expected to fly including to Alaska, Hawaii, and across the US, according to the airline's website. Over 50 hours across 19,000 miles are slated to be put on the aircraft by the airline before March 1.

Alaska did not operate or even take delivery of a Max aircraft before the March 2019 grounding. A February 2019 press release shows that the airline was planning to take delivery of its first Max 9 in the summer of that year but was ultimately unable to do so.

Despite having never so much as flown passengers on the plane, the Seattle-based airline just secured an order for 36 additional models through a deal with Air Lease Corporation and Boeing. In exchange, 10 of Alaska's Airbus A320 aircraft acquired in a merger with Virgin America were sold to ALC.

The new lease leaves Alaska with 68 Boeing 737 Max 9 aircraft currently on order, complementing its predominantly Boeing 737 Next Generation fleet.

Southwest Airlines

Southwest has no current Max flights anywhere in its schedule, Cirium data shows, and CEO Gary Kelly says it won't be flying before March, but that doesn't mean it's not eager to get the Max flying. A Bloomberg report in November revealed that Southwest is in talks with Boeing to acquire up to 30 737 Max "white-tail" aircraft, the name given to planes that have been built but lost their original customer.

As Southwest operates an all-Boeing 737 fleet, incorporating the Max into daily flying after the FAA's required fixes are completed and pilots are trained on the aircraft won't be difficult at all.

A likely candidate for Max flying would be Southwest's routes between the mainland and Hawaii as the long overwater routes offer an opportunity for the Max to provide cost savings to the airline. Southwest had intended to use the Max on Hawaii flights but didn't get the chance before the March 2019 grounding.

Southwest currently has 34 Max aircraft in its fleet with orders for nearly 300 more, according to Cirium data.