SEATTLE — Boeing and its Machinists union reached a tentative four-year settlement to end a strike that has shut down the company's commercial airplane operations since Sept. 6, union and company spokesmen confirmed.

Boeing and the Machinists union said the deal would enhance job security.

Francis "Frank" Larkin, a spokesman for the International Association of Machinists and Aerospace Workers in Washington, D.C., told The Associated Press the deal was reached shortly before 9 p.m. Monday, in the fifth day of talks at Federal Mediation and Conciliation Service headquarters in Washington and the 52nd day of the walkout.

Analysts estimated the strike cost the world's No. 2 commercial airplane maker roughly $100 million a day in deferred revenue and production delays on its highly anticipated next-generation passenger jet.

In a news release, Boeing Commercial Airplanes President Scott E. Carson said the agreement "rewards employees for their contributions to our success while preserving our ability to compete."

Boeing spokesman Tim Healy in Seattle said the settlement includes varying degrees of change in all three parts of the contract that deal with outsourcing — provisions for subcontractors to deliver parts and supplies to the shop floor, procedures for the union to bid for work before it is outsourced and a section on maintenance work.

Healy said it took until Saturday to reach agreement on job security, with the two successive days of talks devoted primarily to economic issues.