KBKhA single-chamber LOX/naphthyl liquid-rocket engine derived from the four-chamber RD-0124A for a proposed Angara-A5 third-stage upgrade. KBKhA publishes 29.5 tf vacuum thrust, 353 s vacuum specific impulse and 160 kgf/cm² chamber pressure; work is paused at the technical-project stage, so no flight or active-service status is asserted.