Sept 18 (Reuters) - Alaska Airlines said

Wednesday it has completed its $1.9 billion acquisition of

Hawaiian Airlines after it reached agreement with the U.S.

Transportation Department.

The airlines on Tuesday agreed to maintain key Hawaiian

routes and adopt consumer protections under an agreement that

will last six years. The Justice Department in August opted not

to block the deal that was announced in December by Alaska, the

fifth-largest domestic U.S. airline, to merge with Hawaiian, the

10th-largest carrier.