the plane carrying the coffin of Queen Elizabeth II was attempted to be tracked by 6,000,000 users in the first minute after the transponder activated, with 4,790,000 following a portion of the flight, becoming the most tracked flight of all time. The website processed 76,200,000 requests related to the flight over its course. Initially, the site crashed due to the sheer number of users. Tracking Flightradar24 aggregates data from six sources: Automatic dependent surveillance – broadcast (ADS-B). The principal source is a large number of ground-based ADS-B receivers, which collect data from any aircraft in their local area that are equipped with an ADS-B transponder and feed this data to the internet in real time. The aircraft-based transponders use the GPS and other flight data input to transmit signals containing aircraft registration, position, altitude, velocity and other flight data. As of 2019, about 80% of aircraft in Europe are equipped with ADS-B and 60% in the US. Airbus aircraft are ADS-B equipped but Boeing 707, 717, 727, 737-200, 747-100, 747-200, 747SP do not come equipped and are not generally visible unless retrofitted by their operators. Typical ADS-B receivers include Kinetic Avionic's SBS-1 and AirNav-systems's AirNav and these receivers are run by volunteers, mostly aviation enthusiasts. ADS-B signals can also be received and uploaded by a low-cost Software-defined radio. As of 2021, Flightradar24 has the largest ADS-B network in the world with over 30,000 connected receivers. Multilateration (MLAT): The second major source is multilateration using Flightradar24 receivers. All aircraft types will be visible in areas covered by MLAT, even without ADS-B, but while 99% of Europe is covered, only parts of the US are. At least four receivers are needed to calculate the position of an aircraft. Satellite: Satellites equipped with ADS-B receivers collect data from aircraft outside of Flightradar24's terrestrial ADS-B network coverage area and send that data to the Flightradar24 network. US/Canada Radar Data FLARM: A simpler version of ADS-B with a shorter range, primarily used by smaller aircraft, in most cases, gliders. The range of a FLARM receiver is between 20 and 100 km. Federal Aviation Administration: The shortfall in the US is mostly made up from five minute delayed data from the Federal Aviation Administration (FAA) but this may not include aircraft registration and other information. Privacy The site blocks some ADS-B information from display for "security and privacy" purposes. For instance, the position of the Japanese