Airlines have less than two weeks to submit bids to the US Federal Aviation Administration to win four new routes to destinations beyond a 1,250mi-perimeter of Washington National Airport.
The FAA has set a 12 March deadline to receive applications for the slot exemptions, which are available to all airlines except American, Delta, United and US Airways. Any comments based on the applications must be submitted by 27 March, or 15 days later.
The four excluded carriers already operate routes exempted from National Airport's 2,012km (1,250mi) "perimeter rule". And each of those airlines can apply separately to add one new route to an airport lying beyond the perimeter.
All eight of the new routes, which form 16 new slot exemptions, are being added under the FAA modernisation and reform act. President Barack Obama signed the new law on 14 February, starting a 90-day clock to assign the four routes to so called "new entrants and limited incumbents".
The perimeter rule at National Airport forces carriers to use nearby Dulles International airport on most routes beyond 2,012km. The perimeter encompasses airports such as Chicago O'Hare and Dallas/Fort Worth International, but excludes Denver International airport and all destinations west.
The FAA has previously granted 24 slot exemptions, or 12 routes, to National Airport's perimeter rule.