FORT WORTH, TEXAS — U.S. carriers are preparing to introduce bus services on some routes as the pilot shortage affects airlines' plans to return to their pre-pandemic flight schedules.

The pilot shortage problem in the U.S. continues to cause problems for airlines to meet the increasing demand for air travel despite higher salaries and bonuses offered by airline operators to attract and maintain talented flight crew.

According to a report published by Bloomberg news agency, United and American signed contracts with the Colorado bus-as-flight company Landline to transport passengers and their luggage by bus on short, domestic routes.

For instance, United takes passengers from Denver to smaller cities by bus, including Breckenridge and Fort Collins.

American is expected to start its bus service starting from June 3rd. Passengers will be transported between New Jersey and Pennsylvania by buses painted by American Airlines' corporate livery. The bus service will not replace aircraft routes. Landline-operated services are incremental to the airline's existing flight schedules, American said.

Another major U.S. carrier Delta Air Lines announced that it was lowering its education requirements to overcome the pilot shortage, including a requirement for a four-year college degree.

United has recently announced that it dropped 29 destinations from its summer schedule because its feeder company SkyWest Airlines didn't have enough pilots to serve those routes.

America's newest regional airline Breeze Airways is trying to solve the pilot shortage by recruiting pilots from Australia under the E-3 visa program.

In contrast to regular airport shuttle services, Landline connections are intended to serve customers with a seamless experience in the same way that regional airlines do.