Planespotting technique that tracks aircraft by measuring the latency in pings from their transponders.
British planespotters told the Register.co.uk they used this method to follow a C.I.A. “rendition aircraft” as it crossed Britain during last year’s hunt for Edward Snowden. The Gulfstream jet hadn’t filed a flight plan and was flying at 45,000 feet, above the mandatory air traffic reporting zone.
Interestingly, the Register reported that this plane used to be a U.S. Air Force general’s “gin palace.”