ST. LOUIS — Boeing officials are planning upgrades for the F-15 beyond those outlined for Saudi Arabia and offered to South Korea, but the company is mum on precisely what is next for the workhorse fighter.

South Korean procurement authorities are expected to announce their choice for a tender of 60 fighters in mid-September, says Steve Winkler, Boeing’s director of business development for the F-15 program.

The Saudi buy of F-15s carries the company’s production line, based in St. Louis, through 2018. A South Korean buy would add about three more years to the life of the production line, Winkler said.

Final bids and pricing were submitted to South Korea Aug. 16. With the Eurofighter Typhoon eliminated from the competition, it is now between the F-15 Silent Eagle and Lockheed Martin’s F-35, which is thought to be more expensive.

With conformal tanks configured to carry weapons internally, Winkler says the F-15 Strike Eagle has front-aspect stealth qualities.

Korea Aerospace Industries is designing the conformal weapons bay and Israel Aerospace Industries is designing the conformal fuel tanks.

Some radar cross-section reduction work is expected to be done to the early stages of the engine and inlet to improve low-observability properties. Winkler declined to say specifically what this work is, but said the design work has already been done and this effort is not developmental.

The F-15 Silent Eagle design is benefiting from work the Saudi government is paying for to develop the digital electronic warfare system and active, electronically scanned array radar.

Also included in the offering is digital fly-by-wire, conformal weapons bays, and the advanced cockpit system featuring 11 x 19-in. color touchscreen displays.

Boeing originally offered South Korea the Raytheon APG-63(v3) radar, but later offered the APG-82(v1) radar.