The needle-nosed jet took off from Brize Norton air force base in Oxfordshire, west of London, at around 1:45 p.m.
In a reverse of Tuesday's flight from London's Heathrow airport, the jet will fly west over the Atlantic before turning around southwest of Iceland and landing at Heathrow just after 5 p.m.
The route is designed to duplicate the operating conditions of Concorde's London-New York route.
The plane is being flown by chief Concorde pilot Capt. Mike Bannister, who also led Tuesday's successful test flight.
The supersonic fleets of British Airways and Air France were grounded after an Air France Concorde crashed outside Paris on July 25, killing 113 people.
Authorities believe a stray metal strip on the runway ripped one of the jet's tires, and rubber debris smashed into the fuel tanks, causing a leak and fire that brought the plane down.
British Airways has since strengthened the wiring in the undercarriages of its seven Concordes, lined the fuel tanks with Kevlar and made other changes meant to prevent fuel leaks. The French tire maker, Michelin, has also developed a new extra-resistant tire to prevent punctures.
BA said the results of today's flight would be submitted to the airworthiness authorities. The airline has said it hopes to resume commercial Concorde flights by late summer.
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