It will be several months if not years before passengers see any significant impact from the merger of American or US Airways.

Passengers with existing tickets on American or US Airways and members of both frequent flier programs shouldn’t fret. No changes will come immediately.

The two airlines said they expect the deal to close in December. But that doesn’t mean everything will happen overnight. When the deal does close, here’s what passengers can expect:

FARES: During the past 5 years, the industry has seen the combinations of Delta with Northwest, United with Continental and Southwest Airlines with AirTran. The price of a domestic round-trip flight has climbed more than 15% since 2009, when adjusted for inflation, according to federal statistics.

The merger will give a combined American and US Airways the ability to increase fares. United, Delta and Southwest would be likely to follow. It could also pave the way for further expansion by discount airlines.

FREQUENT FLIER MILES: Miles will be safe. After the merger closes, the two airlines will likely combine the miles into one program and elite status from one airline will likely be honored on the other. That puts the occasional traveler closer to rewards.

The merged carrier will continue American’s participation in the OneWorld alliance, which was founded by American, British Airways, Cathay Pacific and Qantas. Today, it has 13 airlines including Finnair, Royal Jordanian and Japan Airlines. US Airways will leave the Star Alliance, which includes rival United, Lufthansa, Air Canada and 24 others. Alliances allow passengers to earn and redeem miles on partner airlines.

DESTINATIONS: A key reason for merging is to link both airlines’ networks, creating a system on par with Delta and United.

There is little overlap between the their existing routes. The combined carrier will offer more than 6,700 daily flights to 336 destinations in 56 countries.

US Airways passengers will gain access to American’s international destinations, particularly London and Latin America. American’s passengers will be able to better connect to smaller U.S. cities that US Airways serves.

The combined carrier will have considerable presence in New York, Philadelphia, Washington, Charlotte, Miami, Chicago, Dallas, Phoenix and Los Angeles. It’s unclear how many will keep their levels of service. In past mergers, airlines have promised not to close hubs but have dramatically cut service in once-key cities.