Northwest Airlines, in the first major break with the simplified fare structure adopted by major United States carriers last month, introduced a two-for-one leisure fare last night on all domestic flights except to Hawaii and Alaska.
Intended principally to stimulate family summer travel, the new fare, which allows an adult and a child to fly for the price of one, also shortens the advance-purchase requirement for family travel to a minimum of seven days from 14 days.
Rather than risk losing market share,American, United and Delta will almost certainly match Northwest, even though it will mean unraveling an important part of their new fare structure, introduced seven weeks ago.
Northwest, which serves more than 100 airports in the United States, accounted for about 12 percent of systemwide air traffic last month, compared with American's 20 percent, United's 19 percent and Delta Air Lines' 17 percent.
Since the introduction of the restructured fares -- which feature first-class and full-coach fares aimed primarily at business travelers and seven- and 14-day advance-purchase fares aimed primarily at leisure travelers -- business travel has increased modestly, but leisure traffic has hardly gained, according to Northwest officials.
Moreover, the carrier estimated that last month's restructured leisure fares averaged almost 10 percent more than last summer's fares.
"We felt that isn't stimulative," said John H. Dasburg, Northwest's president and chief executive. "So we decided to entice the leisure traveler back into the marketplace this summer with an affordable product."
Under Northwest's new fare, an adult and a child age 2 to 17 can fly round trip between New York and Chicago for a total of $250. Before last night, the lowest round-trip fare (a 14-day advance purchase) for two people on that route was $500.
And the lowest round-trip fare on that route last summer for two people (on a "companion fare," applicable to child or adult) was $303.
Tickets for the new fare must be purchased no later than June 5 but are valid through Sept. 13, six days after Labor Day. They are non-refundable but, as is true of tickets purchased under the simplified structure announced by American on April 9, flights can be rescheduled by paying a $25 service fee, as long as applicable advance-purchase and Saturday stay-over requirements are met.
While most of the large carriers went along with American's revamped fare structure last month, Trans World Airlines has continued to offer lower fares, particularly for flights booked through its St. Louis hub.
America West, Continental and USAir each have offered low fares over certain routes they consider vital. And even American lowered fares to match Southwest Airlines, the discount airline. But most carriers adhered to the basic four-tier structure.
To qualify for Northwest's new fares, tickets for both child and adults must be purchased at the same time for the same flight. "If you show up at the airport without the other person," said Mark E. Abels, vice president of corporate communications, "you can't get on the flight."
The fare applies to any adult, not just parents but also siblings, relatives and friends. In an unusual interpretation of the regulations, a child is defined as anyone from age 2 to 17, while an adult is defined as anyone age 12 or older.
Northwest said that would allow a family of six, for example, to pair up two children with their parents to obtain the lowest fare, and the remaining two children to pair up -- one as an adult, the other as a child.
Mr. Dasburg said Northwest had no plans to change or reduce business fares.