Block 2 would carry weapons internally, a provision for which would be made in the Block 1 design. Antennas would be conformal, and sensors would be “integrated”—for example, in the radar, radome and apertures. There would be minimal gaps and a radar-absorbing coating on the canopy, and the structure of the aircraft, not just its paint, would absorb radio waves. The result would be an aircraft as stealthy as the F-117, the agency proposes.

Block 3 would advance the aircraft to the level of the B-2, F-22 and F-35, but no details are given.

All of this is a step beyond the previous concept, in which the KF-X would have aimed only at something like the Block 1 standard.

The aircraft is expected to be between the Lockheed Martin F-16 and Boeing F-15 in size. Consistent with that, the agency shows the C103 design with two engines of 18,000 lb. thrust each. According to a 2009 external review of the program, the empty mass of the KF-X should be 10.4 metric tons.

Since work began in 2002, the KF-X has been stuck in feasibility studies, concept definition and preliminary design. The finance ministry last year put a stop to it entering full-scale development this year. Instead it allocated just 4.5 billion won for further studies.

The agency's Lee says that if full-scale development begins in October 2014, the first prototype could be rolled out in August 2019 and fly in September 2020. Two years ago, the South Korean air force said it expected the KF-X or an alternative to enter service in 2021. That would obviously be impossible for a type that made its first flight in 2020.