British Airways has launched an inquiry into an incident on board a Glasgow-bound Airbus A321 from Heathrow that had to turn back after both pilots complained of feeling light-headed.
The flight, which had more than 100 people on board, was abandoned on 20 December, with cockpit crew forced to wear oxygen masks after deciding to return to London.
The incident was highlighted on a pilots' website by a passenger who said they were on board the flight.
Quoted by the Press Association, the web entry read: "At approximately 20 minutes into flight a very abrupt and panicked message came over the PA from the pilot 'senior flight attendant to the flight deck'." Following the announcement, the passenger said the flight attendants looked "worried".
"No announcement for a long time then the expected technical problem line was posted to all. We landed no problem but were met by a full fire service turn out, including local authority fire service and engineers etc etc," said the passenger.
A BA spokesperson confirmed that the crew felt light-headed but, following a thorough check, no fault was found with the plane.
"Our flight crew are highly trained to deal with such circumstances. The aircraft returned to Heathrow, landed safely and customers continued their journey on a replacement aircraft after a short delay," she said.
"We apologise to customers for the inconvenience but their safety is always our highest priority."