British Airways Flight BA295 descended 28,000 feet over Ireland before landing safely at Heathrow. A technical issue forced the return. Here is what is known about the incident and the emergency response.
In aviation, the quickest way down is sometimes the safest way home. That lesson, drilled into airline pilots through years of repeated training, appears to have been put into practice on Monday, October 5, when British Airways Flight BA295 shed roughly 28,000 feet of height over Ireland, turned back and landed safely at London Heathrow.
The facts are now clearer than they were in the first hours. The Boeing 777-200ER left Heathrow’s Terminal 5 at 11.50am for Chicago O’Hare, a journey scheduled to take eight hours and 40 minutes. Flight-tracking data shows that about an hour into the flight, having reached its cruising height of 37,000 feet, it descended in a matter of minutes to about 9,000 feet. The crew set the code 7700 on the aircraft’s transponder and reversed course. The aircraft then flew a holding pattern off the coast of Wales before touching down at Heathrow at around 5pm, after almost five hours in the air.
British Airways has since confirmed that the pilots returned to Heathrow because of a “technical issue”. The airline said the aircraft landed safely, that passengers left it in the normal way, and that its staff were working to rearrange their journeys. It has not said what the technical issue was.
That silence matters. A loss of cabin pressure, known as decompression, is the explanation most widely discussed, since a rapid descent of this kind usually points to a pressurisation problem. But the airline has not confirmed it. A steep descent, by itself, is not proof that decompression took place.
One new piece of evidence does strengthen the case. Footage filmed inside the cabin shows oxygen masks hanging from the ceiling while a recorded announcement instructs passengers to put them on at once. On an airliner, the masks are designed to drop automatically when the pressure in the cabin falls too far, though the crew can also release them by hand as a precaution. Their deployment is therefore consistent with a pressurisation problem, without being final proof of one.
The code 7700 does not settle the matter either. A transponder is a small radio that tells air traffic control who the plane is and how high it is flying. Pilots can type a special four-digit code into it. The code 7700 simply means: this is an emergency, give us priority. It does not say what the emergency is. It may be used for grave technical, medical or operational problems alike.
Why, then, is cabin pressure the leading suspect? At 37,000 feet, the atmosphere is so thin that it cannot push enough oxygen into human lungs for normal breathing over any length of time. An airliner therefore keeps its cabin pumped up with air. It does not recreate sea-level conditions exactly. Instead, the cabin is held at a comfortable equivalent height of several thousand feet above sea level, much like the air of a hill station.
If that pressure escapes, the air inside starts to match the thin air outside. Until the aircraft reaches lower altitudes, the escaping air leaves less oxygen to breathe. The result is hypoxia, a condition in which the brain and body are starved of oxygen. A person may grow confused, feel weak or lose consciousness, and at great heights this can happen with surprising speed. That is why the oxygen masks that drop from the ceiling are so vital a safeguard.
Masks, however, are only a temporary measure. The lasting remedy is to bring everyone down to air that can be breathed without emergency oxygen, which generally means 10,000 feet or lower, depending on the terrain below and the circumstances. A rapid descent from 37,000 feet to about 9,000 feet matches what pilots are trained to do after a pressurisation emergency. Safety experts treat this fast descent as a basic part of handling a pressure failure. Bring the plane down, and the thin air outside becomes thicker air that people can breathe.
A passenger’s account shows how this played out on board. Tom Nicholls told The Mirror that there was a sudden patch of turbulence, and that the masks came down shortly afterwards, leaving some uncertainty in the cabin. A couple seated in front of him could not reach their masks and went looking for a spare seat that had one. By the time they found it, he said, the captain had announced that the aircraft was below 10,000 feet and masks were no longer needed. In other words, the descent did its job faster than two passengers could change seats.
Mr Nicholls also said the manoeuvre did not feel like a rapid descent, and he praised the pilots. That fits the way such a descent is flown. It should never be described as an aircraft “falling”. Pilots deliberately lower the nose, reduce engine power and deploy speed brakes, which add drag much as an open palm held outside a moving car’s window catches the wind. The aircraft loses height swiftly, yet stays under control throughout.
What could cause pressure to be lost in the first place? There is no single culprit. The fault may be in the system that keeps the cabin pumped up with air, in the valves that let air out, in a leaking door or seal, or in some other technical part. Structural damage that opens a larger gap in the pressurised fuselage is a graver possibility, but there is no evidence of this on BA295, and the airline’s own description of a technical issue, followed by a normal landing and disembarkation, does not suggest it. Research into such events shows that many involve pressurisation system components rather than a dramatic hole or complete structural failure.
The long wait before landing now has an explanation as well. Initial reports say the plane circled off the coast of Wales to burn off fuel. A Boeing 777 that has just left for America is too heavy to land without risking structural strain or overheated brakes. It can land overweight if it truly must, but with the aircraft stable at 9,000 feet, the crew had time to lighten it to its maximum landing weight first. This accounts for a flight that turned back after about an hour yet stayed airborne for nearly five.
For those strapped into their seats, those minutes must have felt endless. Until British Airways or investigators say exactly what failed, decompression stays the most probable explanation rather than a confirmed one. Yet if cabin pressure was indeed the problem, the plunge was not the peril. It was the disciplined act of a trained crew, the very action that protects every life on board, and on Monday everyone on BA295 walked off the aircraft.
(Girish Linganna is an award-winning science communicator and a Defence, Aerospace & Geopolitical Analyst. He is the Managing Director of ADD Engineering Components India Pvt. Ltd., a subsidiary of ADD Engineering GmbH, Germany.)