Abstract: A system for correlating secondary surveillance radar (SSR) data and ACARS data which results in a real time correlation of data which are unique to the separate existing systems. More specifically, a method is provided to attach flight identification data from ACARS signals to real time SSR data from Mode S transponders. Aircraft Mode S addresses are decoded and then converted to aircraft registration numbers using an algorithm or lookup table. Registration numbers are then correlated with registration numbers from decoded ACARS signals. The result is a real-time system which may provide an aircraft's registration information, including registration number, owner, make, and model, as well as its current flight identification number, and ACARS messages. As part of an aircraft multilateration system, the system provides an independent air traffic control picture complete with aircraft position and identification by flight number without the use of active radar equipment.