Tui has launched an investigation after two crew members and 25 passengers on a flight from Orlando were affected by nausea and dizziness shortly after take-off.
The Thomson Airways Boeing 787 Dreamliner had just left the Florida airport for Bristol on Sunday when two cabin crew members reported feeling ill.
The aircraft, which had 287 passengers on board, dumped fuel and returned to Sanford airport 45 minutes later. Four people were taken to hospital, with the rest receiving medical treatment at the airport.
A specialist chemical hazards team checked the aircraft, but it remains unclear what caused the incident. The 787’s new design means that unlike conventional aircraft, it does not draw cabin air in from the engines, making fumes from them unlikely to be the cause.
Passengers arrived back at Bristol 24 hours late after a replacement aircraft was sent from the UK. The airline apologised and said it had provided food and accommodation to passengers.
A spokesperson said that investigations into the cause were still being conducted. She added: "The safety of our customers and crew is of paramount importance to us and we would like to reassure everyone that events such as these are rare."