American Airlines flight returned to Heathrow after turning around near Iceland.
Its said that a flight attendant had fainted and five other crew members were ill.
Two passengers on board also felt unwell during the flight.
Doctor on board the flight said that sick cabin crew had reported a burning smell
Dr Barbara Persons was on the flight AA109 to Los Angeles and had offered to help when cabin crew and passengers reported to be feeling dizzy.
The flight declared an emergency after numbers of passengers became ill.
One flight attendant passed out near the business class toilet and the doctor attended to her first. She was placed on oxygen.