South Korea appears poised to order 60 Boeing F-15SE Silent Eagles for its F-X Phase 3 competition, throwing a lifeline to the venerable fighter’s production line and offering the manufacturer an opportunity to improve it for future contests.

Seoul’s Defense Acquisition Program Agency says it has excluded one contender — identified by local media as EADS, offering the Eurofighter Typhoon — because the bidder, with the aim of reducing its price, changed previously agreed upon conditions of its offer without consent. The contentious change was EADS’s alteration of its offer from 45 single-seaters to 54, and 15 two-seat Typhoons to six, says Yonhap news agency.

Yonhap says the third contender, the Lockheed Martin F-35 Lightning, has also been excluded, because its bid did not meet the budget, 8.3 trillion won ($7.5 billion). Lockheed, however, is refuting this assertion, saying it “has not to date received an official notification from the Republic of Korea regarding the results of the price bidding for the F-X Program. The F-X source selection process has multiple phases and we will continue to work closely with the U.S. Government as they offer the F-35 to Korea.”

Boeing is not yet assured of a contract, however, and the air force is likely to keep pushing for the F-35, the type that it has always wanted for the competition.

The F-15SE is a proposed upgrade of the F-15 with features to control radar reflections, but to get into production it needs the South Korean order. Without F-X Phase 3, F-15 production may end in 2019 — and earlier for long-lead items—when the last of 84 new-build F-15SAs for Saudi Arabia are due to be delivered. F-X Phase 3 would prolong production until 2021, 49 years after the type’s first flight.

Boeing’s fighter has had several advantages in the program. Already in South Korean service, it has probably been the cheapest contender, a key advantage given the inability of the agency, constrained by parliament, to consider above-budget bids. Last month it rejected all offers because they exceeded the budget; it then called for new proposals from the competing companies. Lockheed Martin not only had to deal with the high cost of the F-35; it also had to offer the aircraft through the U.S. government’s foreign military sales arrangements, which links the price paid by the customer to that paid by Washington.

An additional advantage of the F-15 is that its major assemblies are already in production by Korea Aerospace Industries. So local manufacturing content, demanded by the agency, should not have driven up costs as much as it did for the other two. The F-15 offers a considerable payload-radius, although all three types meet the requirement in that respect. The type also comes from the U.S., which underwrites South Korean security.

Deliveries of F-15Ks for South Korea and similar F-15SGs for Singapore ended in 2012. Deliveries of Saudi Arabia’s new aircraft are not due to begin until 2015, although Boeing has already rolled out the first and is upgrading 70 F-15Ss to the F-15SA configuration. South Korea bought 61 F-15Ks under F-X Phases 1 and 2. One crashed.

The F-15SE has canted tail fins and can carry four bombs or air-to-air missiles internally, thanks to modified conformal fuel tanks that are optionally attached to the fuselage sides. A new BAE Systems digital electronic warfare system frees up space for more fuel and the airframe is treated with radar absorbent material. Since the F-15K won earlier F-X competitions with a mechanically scanning radar, Boeing has fitted the F-15 with the Raytheon APG-63(v3) radar, which has an active electronically scanning antenna. Since that radar has been sold to Singapore, it is presumably available to South Korea.

Jefferies aerospace analyst Howard Rubel says Boeing’s pursuit of the contract probably underscored its ongoing industrial cooperation with Korean aerospace producers. “The deal would represent a significant success for Boeing and indicate that its efforts to improve the F-15’s survivability have made progress,” he wrote in an Aug. 19 note to his clients. “The range and payload of the plane far exceed the capability of the F-35.”

But Rubel also stressed that the competition is not over until a deal is signed. “Much can happen between one round and the final contract,” he notes. “From Lockheed Martin’s point of view, a win would reinforce the company’s point that stealth and other F-35 system capabilities dominate such factors as range, payload or one versus two engines.”