Baggage included? What about seat selection? Travel sites are scrambling to keep up with new airfare rules

  • The largest airlines are expanding no-frills fares.
  • These tickets are often restrictive but terms vary by region.
Jeff Greenberg | UIG | Getty Images

Buying a coach-class plane ticket isn't as simple as it used to be.

Recently, airlines introduced some of their most restrictive — and perhaps confusing — ticket fares to date, with some not even allowing passengers to access the overhead bins.

Travel sites, including fare search-and-comparison like Hipmunk and Booking Holdings unit Kayak, have recently unveiled new features that aim to highlight what exactly passengers are getting when they buy a "no-frills" fare. On these flights, passengers fly on the cheap without non-essential extras.

For passengers who fail to understand what they're getting in a ticket, the misunderstanding can be both costly and frustrating.

"Basic economy" passengers on American and United, for example, cannot use the overhead bin — and any bags they bring on must fit under the seat in front of them. If the basic economy passenger brings a full-size carry-on to the gate, It'll cost the baggage fee plus a $25 gate-check charge, for a total of $50.

Starting this spring, American will offer basic-economy tickets to Europe. Those passengers can use an overhead bin but they'll have to pay for a checked bag, similar to Delta's international basic-economy tickets.

To help make subtle differences clearer, Kayak launched what it calls a Baggage Fee Assistant, a small pop-up window. It allows users to see whether in-cabin bags are included, and gives them the change to add checked bags, depending on what the ticket allows.

"It gets harder and harder to let users know what they're getting," said Vanessa Kafka, Kayak's vice president of product. She told CNBC that several travelers contacted Kayak, confused by some of the no-frills tickets' rules.

Some sites like Hipmunk, which allows users to compare airfares, make a clear call-out above no-frills fares.

Travelers can also search for tickets by how much mileage they can earn. However, airlines have made it harder to earn miles over the past several years, rewarding passengers based on what they spend, not how far they travel.

Last year, fare-tracking app Hopper introduced Fare Bear, which helps passengers determine the full price of a ticket, including seat assignment, a meal, baggage fees and other add-ons that used to be free.

Airline websites call out basic economy fare restrictions several times in the purchase process, and even give travelers the chance to upgrade before they hit the "buy" button.

As carriers roll out more of these basic economy fares, and a la carte services, some executives have said they measure the product's success by how many passengers pay up to avoid it altogether.