Six airlines won permission Friday to resume scheduled commercial air service from the U.S. to Cuba for the first time in more than five decades, another milestone in President Barack Obama’s campaign to normalize relations between the two countries.

The airlines — American, Frontier, JetBlue, Silver Airways, Southwest and Sun Country — were approved by the Department of Transportation for a total of 155 roundtrip flights per week. They’ll fly from five U.S. cities to nine cities in Cuba other than Havana.

The airlines must begin service within 90 days, although they can request an extension if they need more time. Some of the airlines have been working for months on logistics and have told the department they could start flying in as few as 60 days. Other airlines have indicated they may need as much as four months to get ready.

Approval is still required by the Cuban government, but the carriers say they plan to start selling tickets in the next few weeks while they wait for signoffs from Cuba.

More than a year ago, Obama announced it was time to “begin a new journey” with Cuba. “Today we are delivering on his promise,” said Transportation Secretary Anthony Foxx.

As it considers opening routes to Havana, the department’s selection process has been complicated because airlines have requested far more routes than are available under the U.S. agreement with Cuba. A decision on Havana routes is expected later this summer.

The routes approved Friday were not contested because there was less interest among U.S. airlines in flying to Cuban locations other than Havana.

All flights currently operating between the two countries are charters, but the agreement the administration signed with Cuba in February allows for up to 110 additional flights — more than five times the current charter operations.

American Airlines has been the most aggressive in its approach, requesting more than half the possible slots to Havana plus service to five other, smaller Cuban cities. The airline has a large hub in Miami, home to the largest Cuban-American population. The Fort Worth, Texas-based airline has also been flying aircraft on behalf of charter companies for the longest time, since 1991.

U.S. airlines have been feverishly working to establish relationships with Cuban authorities. For instance, American had a number of meetings this week in Havana with Cuban aviation and banking officials.

“We have been working for months on this plan,” Galo Beltran, Cuba country manager for American Airlines told The Associated Press this week during the trip to Havana. “For us, it is going to be fairly easy because of the experience we have.”

Cuba already has seen startling growth in aviation. Last year, it saw 18 percent more passengers than in 2014, according to government aviation officials.

Currently, 46 airlines fly to Cuba, including Air France, Aeromexico, KLM, Air Canada, Areoflot and Iberia.

Cuban aviation officials say they are ready for the extra flights but that questions remain, especially at Havana’s airport, about where the additional planes will park.

There has been plenty of interest by Americans in visiting Cuba since relations between the two nations started to thaw in December 2014. Nearly 160,000 U.S. leisure travelers flew to Cuba last year, along with hundreds of thousands of Cuban-Americans visiting family.

Most Americans still cannot legally visit Cuba; however, the Obama administration has eased rules to the point where travelers are now free to design their own “people-to-people” cultural exchange tours with very little oversight.

Prices for an hourlong charter flight are about $500, while commercial airlines will probably offer flights for significantly less than that amount, although none have publicly discussed pricing. The check-in process for charters is also a cumbersome one, and the companies lack the traditional supports of commercial aviation such as online booking and 24-hour customer service.

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This article was written by Joan Lowy and Scott Mayerowitz from The Associated Press and was legally licensed through the NewsCred publisher network.

Photo Credit: Jose Marti International Airport in Havana, Cuba. calflier001 / Flickr