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Only about 60-65 % of the aircraft detected by ADS-B reveal their position. The ones that don't are military and private aircraft - business jets, small single-engined turboprops, and old aircraft lacking a GPS belonging to dubious airline companies. You probably came across the term 'MLAT' or 'multilateration' - a triangulation technique that can reveal the position of these aircraft. It requires a special setup (precise timing) of the ADS-B decoder software and a community of MLAT sharers. It might be a good idea to devote an HAK5 episode to this subject? Late March POTUS and his flying circus were in Brussels, Belgium. Obviously none of the aircraft revealed their position, only the ICAO hex address, callsign, and altitude. POTUS took into the air with a fleet of two US Marine Corps Sikorsky VH-3D Sea King (one of which was 'Marine One') and five US Army Sikorsky UH-60A Blackhawk helicopters (to visit the only American military cemetery in the country). The five Blackhawks revealed themselves on ADS-B Mode S, but the two US Marine choppers went a step further - one was invisible altogether, and in the second one its ICAO hex address had been changed to the non-existing '000001', but they forgot to suppress the altitude, hovering around 1,000 feet, revealing that it belonged to an helicopter. MLAT could unsneak the sneakers! I used PlanePlotter/RTL1090 and an RTL2832U/R820T dongle with the original antenna to track their movements. HAK5 fan from Belgium.