Boeing Co. and its white-collar engineers’ union said Wednesday they had reached a tentative agreement on a six-year contract extension, avoiding a potentially bruising fight that would’ve renewed long-standing tensions between employees and management.

The existing four-year contract was set to expire in October, and, if renewed, would provide Boeing with labor stability into the 2020s and shift the last large group of its unionized employees away from a defined benefit pension program.

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