LONDON — A British Airways passenger jet from London to Chicago descended 27,000 feet in just seven minutes on Monday after declaring an emergency because of an unspecified “technical issue,” the airline said.The Boeing 777 took off at 12:15 p.m. local time (7:15 a.m. ET) but made the descent just 30 minutes later while flying over Ireland, according to flight tracking website FlightAware.It turned around and spent around four hours zig-zagging over the Bristol Channel, to the west of England, before landing back at London Heathrow Airport at 5 p.m. local time (noon ET).“The aircraft landed safely after our highly-trained pilots returned to Heathrow following a technical issue,” British Airways said in an emailed statement. “Customers disembarked the aircraft normally and our teams are working to get their travel plans back on track as quickly as possible.”Heathrow did not immediately respond to a request for comment.Passengers will likely be put up in hotels by the airline until another flight can arranged, as stipulated by the U.K. Civil Aviation Authority.This is a developing story. Please check back for updates.