BEIJING — The South Korean air force rates all of the Western competitors for its F-X Phase 3 fighter program, including the F-35 Lightning, as capable of meeting the in-service date of 2016, an assessment that appears to raise the chances of the Lockheed Martin aircraft.

The air force does not express the same view on the fourth and most recent competitor for the planned 60-aircraft order, the Sukhoi PAK FA.

The Eurofighter Typhoon is in service and can therefore meet the schedule, the air force says in an unpublished briefing paper. And although it notes that the F-35 and the Boeing F-15SE Silent Eagle are not fully developed, the air force says they can be ready in time.

That judgment is less important for the F-15SE than for the F-35. The Boeing fighter would be modified for the SE version mainly by introducing fly-by-wire flight controls, adapting its conformal fuel tanks to house weapon bays and by canting the tail fins with a straightforward structural change—objectives that should be achievable well before 2016.

But for the Lightning the air force’s assessment seems to sweep aside concerns that, while the stealth fighter is especially well suited to the air-to-ground part of the F-X Phase 3 requirement, its repeatedly delayed development schedule has become uncomfortably tight for South Korea’s needs.

The U.S. Air Force does not expect its F-35As to be operational until 2018. Its definition of initial operational capability is more demanding than South Korea’s, but the U.S. schedule offers little reassurance for potential buyers that would need the aircraft earlier.

Even if the South Korean air force’s assessment is not realistic, the expression of that view at least means that the service is willing to proceed as if the F-35 complies fully with its requirements. And if the air force is bending the rules for the F-35, then it seems to be showing a preference for it.

On the other hand, the F-X Phase 3 program could be delayed, giving more time for Lockheed Martin to meet the schedule. The company has said it could deliver aircraft to South Korea in 2016—but that is not the same as establishing an operational capability.

In the briefing paper, the air force is silent on the question of whether the PAK FA would be ready in time. The failure to endorse the Russian fighter’s schedule can only raise concerns that the aircraft, a late entry into the race, is regarded as only a stalking horse for the Western fighters.