That smashes the previous record, achieved just last month during US House Speaker Nancy Pelosi's controversial visit to Taiwan. Her plane's journey to Taipei was tracked by about 2.9 million people.
Inside Flightradar24, the website that tracks every plane in the sky
The Royal Air Force plane carrying the Queen spent one hour and 12 minutes in flight. It landed at RAF Northolt, a military station about six miles from Heathrow Airport in Greater London.
From Northolt, the Queen's coffin was taken to Buckingham Palace. On Wednesday, September 14 the coffin will be escorted to Westminster Hall, Parliament, where the Queen will lie in state until her funeral on Monday, September 19 in Westminster Abbey.
Nancy Pelosi will not be attending, although President Joe Biden and First Lady Jill Biden will.
The RAF C-17 globemaster plane transported Her Majesty's coffin.
Andrew Matthews/Pool/AFP/Getty Images
Flightradar24 is one of several increasingly popular plane-tracking tools. The site began in Sweden in 2006 and became publicly accessible three years later.
Its first significant moment of mainstream attention came in 2010, when the Icelandic volcano Eyjafjallajokull's eruption grounded and rerouted thousands of flights throughout Europe and North America.
Ian Petchenik, the website's director of communications, told CNN Travel that the resulting traffic spike "was certainly our first foray into international events, and how displaying air traffic to the public in real time could influence how people were thinking about world news."
Before Pelosi's Taiwan visit, the most popular flight search on Flightradar24 was opposition leader Alexei Navalny's flight back to Russia, where he was going to be put in prison upon arrival in 2021.
You can now drink beer made by the Queen -- or, at least, her estate
Flightradar24 staffers knew that the Queen's final air voyage had potential to become tremendously popular. Their team tried to provide as much website stability as possible, but the massive influx of new users proved a technical challenge.
"This immediate, massive spike was beyond what we had anticipated," Petchenik wrote in a blog post. He added: "In total we processed 76.2 million requests related to this flight alone -- that's any action by a user, like clicking on the flight icon, clicking on the aircraft information in the left side box, or adjusting settings."
He predicts that this particular flight search record will remain unbroken "for a long while."
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During her seven-decade reign, Queen Elizabeth traveled the world, making royal visits to places as far-flung as Bermuda, Nepal, Ghana, Mexico, Pakistan, Australia and Russia.
One of her final high-profile appearances was in May of this year, when she attended the opening day of the Elizabeth Line, a new London tube line named in her honor.