'Basic Economy' fares now on sale at American, United

And then there were three. American and United each began sales of their new “Basic Economy” fares on Tuesday, matching rival Delta in an effort by the "big three" U.S. airlines to fight back against encroaching budget carriers.

American and United had already announced their intentions to add Basic Economy fares, which cost less than standard coach tickets but come with notable restrictions. Now, they've followed through with the first sales of such fares. Delta became the first to introduce such a fare type more than two years ago.

American’s Basic Economy fares rolled out on Tuesday on 10 different routes from four of its hub airports: Charlotte, Dallas/Fort Worth, Miami and Philadelphia. The new fares show up on flights from March 1 onward.

American latest to add 'Basic Economy,' carry-on restrictions

United adds 'Basic Economy' fares with carry-on bag restrictions

United followed American later Tuesday by revealing that its first Basic Economy fares had gone on sale on certain flights between Minneapolis/St. Paul and seven of its hub cities (Chicago O’Hare, Denver, Houston Bush International, Los Angeles, Newark, San Francisco and Washington Dulles).

While American and United each had previously announced plans for basic economy fares, their same-day rollout of the fare type appeared to be a coincidence. Delta is already selling such fares after formally announcing them in 2014.

The fleet and hubs of United Airlines, by the numbers

The fares – roughly $20 to $40 cheaper per round-trip – come with restrictions. Among the most notable, American and United will not allow Basic Economy customers to stow carry-ons in overhead bins. (Delta has no such provision). Basic Economy customers also will be among the last to board the plane and – generally – will not be able to select seat assignments in advance. Basic Economy fares will truly be nonrefundable; changes will not be permitted, not even for a fee.

The new Basic Economy fares now in place at the USA's three biggest airlines have been developed as a weapon to battle a new breed of budget carriers rapidly expanding at major hubs.

Those discounters – notably “ultra low-cost carriers” such as Spirit, Frontier and Allegiant – are known for charging rock-bottom base fares but adding fees for everything from seat assignments to water. They also charge a fee for using their overhead bins. But, despite their fee-heavy structures, those budget outfits often compare favorably to major "full-service" airlines in online fare searches.

The bigger airlines view the new Basic Economy fares as something to help them combat that in an age where the most price-sensitive customers will simply book on an airline with a cheaper fare – even for savings of as little as $1.

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The fleet and hubs of American Airlines, by the numbers

Now flying on American: Real international-style premium economy seats