Southwest Airlines joins its rivals in offering free onboard movies. What’s the catch?

Southwest Airlines, the nation’s most popular domestic carrier, is providing its passengers with free movies to match the onboard entertainment already offered by most of the carrier’s biggest rivals.

The Dallas-based carrier has already begun rolling out the free movies on some planes, with plans to roll the service out by the end of the week to all customers who fly on planes with wireless internet.

Southwest is playing catchup with its rivals American, Delta, United and Alaska, which already offer free entertainment, most of it available for streaming on the portable electronic devices that passengers bring on the plane.

The carrier was one of the first to offer free streaming television, but is now the last of the major carriers to offer free movies. Although carriers such as Delta and JetBlue offer movies, television and other forms of entertainment on seatback screens, Southwest has stuck with offering entertainment that can be viewed on the devices that passengers bring with them — a less expensive alternative that helps Southwest keep prices low.

“We pivoted early on live TV before anyone else,” said Southwest Airlines spokesman Brad Hawkins. “We are now rounding out that suite of complimentary offerings.”

Seth Kaplan, editor of Airline Weekly, a trade publication, said Southwest Airlines may simply be offering free movies to better compete with its rivals that already have the service.

“This is them trying to match the in-flight entertainment offerings of other airlines,” he said.

But there might be other ways airlines can benefit financially from offering free movies. To watch the movies, most of the large carriers direct passengers to download the airline app to their phone, tablet or laptop.

The airline apps can be used to “upsell” passengers to other services.

In addition to giving passengers “check in” reminders and other alerts about their flights, the Southwest Airlines app includes an enrollment form for fliers to join the carrier’s loyalty reward program and tempts them with links to book a rental car or hotel room with businesses that have a partnership with Southwest Airlines.

Henry H. Harteveldt, a travel industry analyst with Atmosphere Research Group, said airlines may also be able to use their apps to collect data about passenger preferences, such as what entertainment they prefer.

But he thinks one of the primary reasons airlines are offering free movies is to distract and entertain passengers so they won’t be as upset about all the other services and products they must already pay for on their flights.

hugo.martin@latimes.com

Twitter: @hugomartin