The DOT approved Alaska Airlines and Hawaiian Airlines to close their merger, although it still must clear the airlines to combine their operations.

On Wednesday, Alaska Airlines acquired Hawaiian Airlines in a historic merger. The acquisition is the largest merger between U.S. carriers in eight years.

The U.S. Transportation Department said on Tuesday it had agreed to allow Alaska Airlines to close on its $1.9 billion acquisition of Hawaiian Airlines , after the carriers agreed to maintain key Hawaiian routes and adopt consumer protections.