Southwest Airlines Co. negotiated for three years, but it finally stroke a tentative agreement with the Transport Workers Union (TWU) of America Local 556.

The union, which represents a hefty number of 14,500 flight attendants of the airline company, recently said that a final version of an agreement was drafted.

Two weeks prior, deals were struck with unions that represent the pilots and maintenance technician staff belonging to Southwest Airlines Co.

According to the internal code of TWU Local 556, all tentative agreements have to first pass a review of the executive board of the union. As the executive board has yet to take a stance on the agreement, its details were not publicly released.

After the board makes its comments on the agreement, the flight attendants must provide a ratification ballot. Only after that ratification vote is cast can the contract go into full effect, provided that a majority of members voted "yes."

Audrey Stone, the president and lead negotiator of TWU Local 556, commends the members of the union for being "the best flight attendants" in the air travel industry and points out that the quality of their services is outstanding.

"We deserve a contract that recognizes that dedication and professionalism," she notes.

It took even longer for pilots from Southwest to reach an agreement in principle. This August, after four years of intense negotiations, the union led a no-confidence vote against Gary Kelly, the helm of Southwest.

The reached agreement reads that pilots will be getting an instantaneous salary boost of 15 percent, with 3 percent per annum increases and a ratification bonus to boot.

Later this month, the Southwest Airlines Pilots' Association will review the new deal and take a vote on whether or not to ask a membership vote to ratify the agreement. According to the Wall Street Journal, the process could take until November.

When looking at the maintenance techs' agreement, it is still pending approval from the executive committee of its union, the Aircraft Mechanics Fraternal Association. After the committee passes the agreement, technicians will cast a ratification vote for its final form. That deal also required more than three years of negotiations.

There might not be a coincidence that a slew of preliminary contracts have recently landed.

This August, Randy Babbitt, the senior vice president of labor relations at Southwest, announced his retirement from the company.

According to the leader of Southwest Airlines Pilots' Association, Capt. Jon Weaks, the unions hailed Babbitt's retirement as a big step forward toward driving the negotiations to an end.

In February 2016, another TWU local representing 12,000 Southwest ground workers signed a new five-year labor contract by only 75 votes.

The number of airline passengers has been increasing over the past years, putting extra pressure on pilots, flight attendants and grounded maintenance personnel.