The merger between Alaska Airlines and Hawaiian Airlines is official, making it possible to share loyalty benefits between both carriers.

Alaska Airlines closed its $1 billion purchase of Hawaiian Airlines on Wednesday, a day after the federal government removed the last major regulatory obstacle to the deal.

The DOT also required both airlines to guarantee fee-free family seating and preserve service to small, rural communities in both Alaska and Hawaii, among other requirements. “Our top priority is protecting the traveling public’s interest in this ...