British Airways Chicago flight returns to Heathrow after emergency descent over Irish Sea

A British Airways flight from Heathrow to Chicago turned back and made an emergency return to London on Monday 5 October. The aircraft had made a steep descent over the Irish Sea after a reported loss of cabin pressure.

Flight BA295, a Boeing 777, left Heathrow's Terminal 5 at about 11.50am for Chicago O'Hare International Airport. The trip normally takes more than eight hours.

Less than an hour into the flight, the aircraft was south of Dublin. Flight tracking data showed it dropping from a cruising height of around 37,000ft to about 9,000ft in a matter of minutes.

The crew declared an emergency and turned the aircraft back towards London. Passengers reportedly said the oxygen masks dropped from the cabin ceiling during the descent.

Hours spent burning fuel

The aircraft was carrying enough fuel to cross the Atlantic, so it could not land straight away. It spent several hours flying in a holding pattern over the Bristol Channel and south-west England, between Pembrokeshire and North Devon, to burn off fuel and bring its weight down.

It then flew back east and landed safely at Heathrow in the late afternoon, almost five hours after it took off.

Long-haul aircraft usually burn or dump fuel before an unplanned return. They take off much heavier than the maximum weight they are designed to land at, and landing overweight puts extra strain on the aircraft.

What British Airways said

British Airways has not said exactly what went wrong. It said only that the pilots returned to Heathrow because of a technical issue.

A British Airways spokesperson said: "The safety of our customers and crew is always our top priority, and the aircraft landed safely after our highly trained pilots returned to Heathrow following a technical issue."

The airline said passengers left the aircraft normally. Its teams were working to get people's travel plans back on track, and many passengers were rebooked onto flights to Chicago the next day.

Why aircraft descend so quickly

When the pressure system on an airliner fails, or crew think it may be failing, pilots are trained to descend quickly to about 10,000ft or lower. At that height the air holds enough oxygen for people to breathe normally without masks.

Messages from the aircraft reportedly showed that pressure in the cabin had dropped to the level normally found at about 10,500ft. That is one of the signs crews watch for before starting an emergency descent.

Passengers' masks hold enough oxygen to last until the aircraft reaches a safe height. To people on the ground, or watching on tracking websites, the rapid drop can look alarming. Aviation experts say it is a routine and controlled step, practised regularly by pilots.

An emergency of this kind is signalled to air traffic controllers with transponder code 7700, the code for a general emergency. That alerts controllers to give the aircraft priority.

No injuries have been reported. British Airways has not given any more detail about the technical fault or about when the aircraft went back into service.