American Airlines said it chose to continue with the flight because of the full load of passengers waiting at London's Heathrow airport to return to the United States.
"With such a small passenger load we did consider whether we could cancel the flight and re-accommodate the five remaining passengers on other flights," says American Airlines' European spokesperson Anneliese Morris.
"However, this would have left a plane load of west-bound passengers stranded in London Heathrow who were due to fly to the U.S. on the same aircraft."
Morris was quick to point out that despite the staggeringly low passenger count, the flight did carry a full cargo load.
"We sought alternative flights for the west-bound passengers but heavy loads out of London meant that this was not possible. The only option was to operate the flight," Morris said.
"This put the aircraft in London Heathrow for the following day, enabling us to operate a full schedule and avoid further inconvenience to our passengers and cargo customers."
________________
Kieran Daly, air transport intelligence editor for Flight International magazine, said the amount passengers carried was irrelevant.
"Airlines are still a business. The cargo had to be flown and perhaps some of it was time-sensitive," Daly said.
"It's just not practical for an airline to tell its customers that it won't fly until it has a full passenger load. Customers won't be happy and the airline will quickly be out of business."