Aug 29 (Reuters) - Southwest Airlines ( LUV ) began

Friday flying its first jet with a secondary barrier to the

flight deck designed to prevent intrusions.

The plane - a Boeing 737 MAX 8 which was delivered in

recent days - took off Friday afternoon from Phoenix to Denver,

the airline said.

Secondary barriers -- long sought after the Sept. 11, 2001

attacks that exposed the risks of inadequate flight deck

protection -- are crucial to aviation safety, pilots unions have

argued.

The flight is a milestone that marks the beginning of the

roll out of the safety feature across the new U.S. commercial

airline fleet in the coming years.

Boeing ( BA ) and Airbus told Reuters they have

begun delivering airplanes with the barriers under the Federal

Aviation Administration regulation announced in 2023 that took

effect on Monday.

Last month, the FAA agreed to give airlines until late July

2026 to put the barriers in newly delivered planes into use.

Most major carriers have told the FAA they plan to take

advantage of the extension and not immediately begin using the

barriers.

Southwest ( LUV ) has opted to immediately begin complying as they

take delivery of new airplanes and expects to take delivery of

about 25 additional Boeing ( BA ) airplanes this year that will have

the barriers.

"We felt like we could get it done and put it in

production as soon as the aircraft was ready," said Justin

Jones, Southwest's ( LUV ) executive vice president for operations

After the hijacking of four U.S. airplanes on September 11,

2001, the FAA adopted standards for flight deck security to make

them resistant to forcible intrusion and unauthorized entry.

The FAA rule requires aircraft manufacturers to install a

second physical barrier on new planes used in commercial

passenger service in the United States, but does not require

existing planes to be retrofitted. Plane makers without FAA

certification of barriers do not yet need to be in compliance.