A Charm City offensive

The Boston-Baltimore competition reflects the growth and aggressiveness of the low-fare carriers, which are entering new markets at a time when overall air travel is down 21 percent from a year ago, according to the Air Transport Association. Before, the low-cost airlines would go into markets to undercut the big legacy carriers, but now they’re increasingly forced to compete with each other. The battle these airlines are engaged in might be a losing one. Baltimore is the 10th most popular destination out of Boston, generating 460,000 passengers a year, but airline analysts say the market might not be big enough for all three low-cost carriers.

“This is like executive chefs fighting over a can of spam,’’ said aviation consultant Mike Boyd.

So why the big fuss over spam? Space, for one thing. The three carriers are already in or eyeing interna tional markets such as Mexico, Canada, and the Caribbean, but the tight race for the Boston-Baltimore route shows that there isn’t an unlimited number of untapped US markets for the low-cost carriers to enter.

JetBlue, AirTran, and Southwest all made money in the second quarter - a relative rarity in the airline industry, which lost $55.4 billion between 2001 and 2008, according to the air transport group - and JetBlue and AirTran are the only two airlines with more capacity than they had two years ago. The low-cost carriers are also going after bigger markets and taking passengers away from the legacy airlines. Delta, the only legacy carrier that had been flying the Boston-Baltimore route in the past year, left the market before the competition heated up.

“The airlines are recognizing that most of the ripest fruit has been picked from the tree,’’ said Henry Harteveldt, principal airline analyst for Forrester Research. As to whether there will be similar competition across the country? “I think everyone’s going to watch to see how Boston to Baltimore plays out.’’