Delta Air Lines (DL, Atlanta Hartsfield Jackson) stands the possibility of losing its Seattle Tacoma International to Tokyo Haneda route allocation after the US Department of Transportation (DoT) ruled that American Airlines and Hawaiian Airlines claims concerning Delta's alleged underutilization of the sought-after Tokyo Haneda slot are in fact worthy of further examination.

In their respective complaints filed with the DoT in October this year, American and Hawaiian claimed that Delta's decision to operate a limited season service in the Seattle-Haneda market, with only 17 planned operations over a 182 day period over the period October 1 until March 28, 2015, represents a gross underutilization of the much-prized slot.

Both called for a review of the slot's allocation with each pitching their own individual proposals. American has offered to start a year-round daily Los Angeles International to Tokyo Haneda flight beginning January 15, 2015, while Hawaiian would provide year-round service to Haneda with full utilization of the slot pair.

In its defence, Delta claimed that its utilization of its Seattle-Tokyo Haneda slots not only meet the DoT's [90-day] dormancy condition, but also complies with a departmental precedent that when a carrier holding unused frequencies has “firm plans” to use them, those frequencies will remain with the holder and not be reallocated.

However, the DoT dismissed Delta's defence in its ruling stating that above all else, the public interest needed to be considered, as in this instance, there is proof the slot is not being adequately used.

"The Department does not need to decide whether Delta’s current level of Seattle-Haneda service triggers the dormancy condition. Where frequency allocations are not being operated effectively, the Department has the authority to reallocate them to ensure that they are used effectively and in a manner that promotes competition and otherwise best serves the public interest. The Department finds that the public interest warrants a proceeding to determine whether it remains in the public interest to allow this limited Haneda opportunity to remain with Delta for service at Seattle, or whether the public interest favors an alternative use of the authority," it said.

Given the urgency of the matter, a decision is expected by late January.