Updated for 2024. With the FAA re authorization act of 2024, there are now 50 slots allowing operations beyond the 1,250 mile perimeter, supporting 25 round-trip destinations. See table below.

I often see posts like, "I want my airline to fly from DCA to XYZ", where XYZ is beyond 1,250 miles from DCA. Some folks are not aware of the Perimeter Rule which limits how far scheduled flights are able to operate into and out of DCA. The current limitation evolved since National opened in 1941 leading to the 1,250 mile restriction we have today. In 2000, Congress made the first of several exemptions for DCA flights to operate beyond the perimeter, which they expanded in 2003 and 2012. This literally takes an act of Congress and we have 40 slot exemptions today. They authorize the DOT to choose the airlines and destinations (2 slots in each direction). The only exception to this was part of the 2012 authorizations, when Congress authorized the "big 4" at DCA (AA, US, DL, UA) to reallocate one slot pair each from a within-perimeter destination to one outside of the perimeter at their discretion, i.e. they could pick any destination..

I went back and researched the initial exemptions (operators and destinations) to where the slots have evolved currently, represented in the table below.

Hopefully you guys find this helpful (or at least interesting)