Southwest Airlines appears to be inching ever-closer to launching its long-anticipated service to Hawaii.

The carrier plans to make its first flight to the state this week, the airline confirmed Monday.

But there won't be any passengers on board. Instead, the flight from Oakland, California, to Honolulu, will be a proving flight that's part of Southwest's effort to secure the "ETOPS" certification it needs from the Federal Aviation Administration to operate long overwater flights with its two-engine Boeing 737 jets.

The airline's first Hawaii flight is scheduled for Tuesday, "barring any unforeseen changes," Southwest spokesman Brian Parrish said in a statement to USA TODAY's Today in the Sky blog.

"Tomorrow's validation flight is not a regular, scheduled flight and only FAA Representatives along with Southwest ETOPS Program Team Representatives and ETOPS-trained Southwest Pilots will be onboard to demonstrate our long range navigation and communication procedures and equipment," Parrish added, noting that additional steps will be required to receive the certification.

"Once we pass all phases of the ETOPS application process to the satisfaction of the FAA and receive our ETOPS authorization, we will announce further details of timing for selling and operating flights," he said.

Southwest had already been in the process of securing that needed certification, but the effort received an unexpected delay during the federal government shutdown that furloughed federal workers, including FAA inspectors.

Speaking during the airline's earnings call in late January, Kelly said he expected that his airline would be able to begin Hawaii flights approximately six to eight weeks after the FAA approval process resumed. Before the shutdown, he said, Southwest was aiming for a Feb. 1 startup, though it never publicized that target date.

He suggested then that if the shutdown ended within a week - which it did - the airline might be able to begin passenger flights by mid-March. One potential trouble spot, however, is that a deadline looms later this month for another possible shutdown.

Whenever its Hawaii service does begin, Southwest's first flights will be from California to Hawaii. Inter-island flights would come after that, though the airline has not provided any sort of time frame.

For now, Southwest continues its efforts to secure the certification that would allow its 737s to fly between the U.S. mainland and Hawaii. The certification - short for "Extended-range, Twin-engine Operational Performance Standards" - is standard for airlines wishing to deploy two-engine aircraft on long overwater routes where diversion airports are scarce.

As aircraft technology has advanced in recent decades, the certification has become common. From the mainland U.S., it's frequently used for widebody jets making long-haul transoceanic routes to Europe and Asia. For Hawaii flights, many U.S. airlines already have ETOPS certification to fly narrowbody planes to and from the state.

While many of its U.S. rivals already have the certification, Southwest's effort to seek it is a recent development. Since its launch in 1971, the carrier flew only within the mainland United States for more than 40 years. But that changed in 2014, when Southwest began flying to several destinations in the Caribbean. It has since expanded its footprint to include Mexico and Costa Rica, but none of those flights require ETOPS certification. But, with the planned Hawaii service, Southwest has finally had to seek approval for ETOPS service.