Earlier this year, Milwaukee's General Mitchell International Airport conducted a survey of nearly 2,400 travelers and found that 48 percent of respondents flew through an alternative airport, only 19 percent of adult travelers who search air fares online always or often look at alternative airports and more than half of U.S. travelers "are not taking advantage of fare savings by searching for alternative airports."
Clearly, Mitchell Airport, an alternative airport to Chicago's O'Hare International Airport, has a very specific ax to grind: The folks there want more travelers from Chicago's northern suburbs to fly through Mitchell instead of through O'Hare. But the survey has a wider application -- and in a wider set of circumstances.
To me, an alternative airport is any field with commercial service other than the most obvious -- and usually proximate -- airport to your home or your destination. And you have several cases when you might want to consider such an airport at either end of your trip:
The main reason to consider an alternative airport is to find lower fares. This situation arises most often in cities that are "fortress hubs" for a giant line, such as Atlanta and Minneapolis for Delta, Houston for Continental, and Dallas-Fort Worth for American. This is the centerpiece of Milwaukee's case: It claims that average fares from Milwaukee to common destinations are $108 less than at O'Hare and $17 less than at Chicago's Midway Airport.
The opportunity to find lower fares at alternative airports is especially attractive where a really small regional airport has service from a low-fare airline that specializes in small-city deals. In the case of Chicago, however, you wouldn't always go to Milwaukee; instead, you might go to Rockford, where Allegiant and Direct Air offer less-than-daily flights to a handful of the nation's top tourist destinations at very low fares.
Parking often costs less at alternative airports than at the giant hubs. Again, Milwaukee claims its rates for comparable parking are less than half the rates at O'Hare.
Security, access to rental cars and other processing factors are usually easier and less stressful at smaller airports than at giant hubs.
On the other hand, if you live in or head for a small community with limited air service, you may want to use a more distant large airport with better service and lower fares. I know from that case: Fares at my home airport, Medford, Ore., can be very high to/from cities not linked by a line such as Allegiant. I find, for example, that maybe half of the travelers I know who live here often drive to Portland or Sacramento airports -- about 300 miles either way -- to find better and cheaper air service.
When you consider an alternative airport, you have to factor in the access. Often, a more distant alternative airport will have little or no convenient public transportation to/from an adjacent big city. If you don't drive, you have a problem. From Milwaukee, for example, public transit to Chicago is on Amtrak, with seven daily trains that run two to three hours apart, and there is no good public transportation at Rockford. You find the same problem at other potentially attractive fields, too; Islip, on Long Island, is a long shuttle-plus-train schlep into Penn Station, and there is no good public transportation between Steward Field, near Newburgh, and New York City.
Be especially careful in Europe: Some big low-cost airlines use fields far from the city they're supposed to serve. Ryanair's German base at "Frankfurt-Hahn," for example, is actually 75 miles from Frankfurt, with no direct rail service, and its "Paris" airport at Beauvais is 50 miles from Paris, also with poor access.
As long as you're careful to avoid local airport access problems, I concur with Milwaukee's overall recommendation: Check alternative airports. Most of the big online travel agencies offer you an easy option. Just click on that "search alternative airports" box -- it costs you nothing -- and you can sometimes knock your air travel bill down significantly.