Frontier Airlines (F9, Denver International) and Spirit Airlines (NK, Fort Lauderdale International) have sued the US Department of Transportation (DOT) over the allocation of slots at Washington National. Both argue that they should have been awarded two slots, while asserting that Alaska Airlines was ineligible due to its codeshare agreement with American Airlines.

In January 2025, Frontier Airlines petitioned the Court of Appeals for the District of Columbia Circuit to review the DOT’s order granting two slots exemptions at Washington National to Alaska Airlines, American Airlines, Delta Air Lines, Southwest Airlines, and United Airlines, enabling them to operate new non-stop round-trip services beyond the airport’s 1,250-mile perimeter (2,012 kilometres). Alaska was granted the slots to operate a daily service from Washington to San Diego International.

According to Frontier, it should have qualified as a “limited incumbent” (meaning a carrier that holds fewer than 40 slots at the airport) and therefore have been eligible for the two slot exemptions reserved for limited incumbents, which were ultimately granted instead to Alaska Airlines. However, the DOT ruled that Frontier was a “new entrant” because it had never held permanent slots at Washington National.

Alaska Airlines should not have been granted the slots due to its codeshare partnership with American which already provides the carrier with “meaningful access to the DCA market,” Frontier argued. Alaska intervened in the lawsuit and requested the court’s authorisation to defend itself in the case, siding with the DOT.

In March 2025, Spirit Airlines intervened in the case as well, joining Frontier in support. However, it claimed that it, rather than Frontier, should have been considered a “limited incumbent” because, while it does not currently operate at DCA, it did so between 2008 and 2012 when it flew from Washington National to Fort Lauderdale International and Myrtle Beach International.

Spirit urged the court to vacate the DOT’s final order related to the two “limited incumbent” slot exemptions, recognise that Alaska Airlines is statutorily barred from receiving these slots, and direct the DOT to reallocate them, allowing both Spirit and Frontier to compete head-to-head with their proposals.

Frontier Airlines was looking to operate a daily service to San Juan Luis Muñoz Marin, while Spirit wanted to serve San José, US.

In a statement to ch-aviation, Alaska Airlines said the DOT's decision came after months of thorough consideration. "The new SAN-DCA roundtrip flights fulfil Congress’s key objective of connecting airports that currently do not have nonstop service, providing passengers to and from the eighth-largest US city, including the nation’s largest military community, with new and better options. We look forward to launching the service on March 17."