British Airways flight BA295 declared an emergency while flying over Ireland on Monday after the aircraft made a rapid descent from its cruising altitude.The Boeing 777 was travelling from London Heathrow to Chicago O'Hare when it descended from around 37,000 feet to approximately 9,000 feet while crossing Ireland.Flight-tracking data showed the aircraft's sudden change in altitude.The flight circled over the Bristol Channel after turning back towards the UK. The aircraft may be holding in the area to burn off fuel before landing, a procedure sometimes used when an aircraft needs to reduce its weight before making a precautionary landing.However, the flight landed back at London Heathrow after a reported pressurisation problem.