Abstract: A passive method for an aircraft to use its on-board locating apparatus to monitor interrogation signals and ISLS signals transmitted by at least one secondary surveillance radar, and coded reply signals transmitted by at least one fixed ground transponder; to match said transponder reply signals with said ISLS signals, in order to associate said transponder reply signals with interrogations from said radar; to repetitiously compute said aircraft's instantaneous position in space, said computations being based on hyperbolic and linear functions related to said aircraft, said radar, and said associated fixed transponder; and to display said positions for navigational purposes.