It’s finally kicked in.

Though United Airlines and US Airways had their marketing alliance approved in October, their code-sharing agreement didn’t take full effect until January. The partnership allows the airlines to sell tickets on each other’s flights, coordinate schedules and offer reciprocal perks such as frequent-flyer miles and use of either carrier’s airport lounges.

United passengers now have access to 14 additional cities in the East and Southeast, while US Airways customers initially gain service to Oakland, Sacramento and San Jose, Calif.; Portland, Ore., and Salt Lake City, and more flights to other Western cities. More code-sharing flights are to be made available later.

In addition, elite-level members in each program may earn 25 to 100 percent mileage bonuses on paid flights on the other airline.

United said the sharing arrangement will be expanded to US Airways’ expanding Caribbean route network and United flights to Asia, Europe and Latin America.

Starting March 1, Mileage Plus elite members (Premier, Premier Executive and Premier Executive 1K) will have their elite status recognized on US Airways with the following benefits: priority boarding, check-in, security and waitlist. And beginning April 1, Mileage Plus members will be able to call reservations to redeem miles for award travel on US Airways.

Both carriers continue to operate under Chapter 11 bankruptcy protection, but the hope is that this alliance will keep other carriers from muscling in on their market share.