The two men are believed to have clung on to the British Airways plane as it flew from Johannesburg in South Africa to Heathrow.
The victim fell on to a shop in Richmond, south-west London, which was below the flight path, yesterday morning.
The second man, aged between 25 and 30, is in a serious condition in a west London hospital after miraculously surviving the ordeal. He was discovered alive by staff at Heathrow.
"A postmortem examination will be held in due course and inquiries are ongoing to establish the male's identity. No arrests have been made. In regards to the male who survived, police were alerted at 8.28 AM on June 18 to reports of a suspected stowaway on a flight from Johannesburg to Heathrow," she was quoted as saying by The Guardian.
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Incidents like these have been reported earlier as well when stowaways have plunged to their deaths in the streets of west London after smuggling themselves on to planes.
They hide themselves in the landing gear where they are exposed to the elements and have to endure plummeting temperatures. Most are killed by the cold and lack of oxygen at high altitudes.
In September 2012, Jose Matada, 26, died after falling from the undercarriage of a Heathrow-bound flight from Angola on to a quiet street in Mortlake, west London.
He died after facing temperatures of minus 60C during the four-hour flight.