Why do planes fly so high, and why do your ears pop when you fly?

TUREFF• •0

Look out of the window on a long flight and you are often around seven miles up, far above the clouds. It seems like a lot of effort to climb that high just to come back down again. There are good reasons for it, and they are connected to the reason your ears pop.

Why airliners cruise so high

Large passenger jets usually cruise somewhere between about 30,000 and 40,000 feet. Several things make that height attractive.

Thinner air means less drag. Air at cruising altitude is far less dense than at sea level, so there is less resistance pushing back on the aircraft. Less drag means less fuel burned for the same distance.
Jet engines are designed for it. Modern turbofan engines run most efficiently in the cold, thin air found high up.
Above most weather. Much of the cloud, rain and turbulence that affects flying is lower down, so climbing above it usually gives a smoother ride, though not always.
Room to organise traffic. Air traffic control separates aircraft by height as well as by distance, and a wide band of cruising levels makes that easier.
Height is a safety margin. In the rare event of a problem, more height gives the crew more time and more options.

Why not fly even higher?

There is a limit. Wings need air to produce lift, and engines need air to burn fuel. Go too high and the air becomes so thin that the aircraft has to fly very fast just to stay up, while the engines struggle. Each aircraft has a best cruising height that depends on its design and how heavy it is. As fuel is burned off on a long flight, the aircraft gets lighter, so pilots often climb in steps to higher levels as the journey goes on.

The air in the cabin

At cruising height the outside air is far too thin to breathe comfortably, so the cabin is pressurised. It is not kept at sea-level pressure, though. Most airliners keep the cabin at a pressure similar to being somewhere around 6,000 to 8,000 feet up a mountain. That is a compromise: it is comfortable for healthy passengers, while keeping the pressure difference across the aircraft's body small enough that the structure does not need to be heavier. This is also why a bag of crisps puffs up during a flight, and why some people feel a little more tired or dehydrated than usual.

Why your ears pop

Behind your eardrum is a small air-filled space called the middle ear. It is connected to the back of your throat by a narrow passage called the Eustachian tube, which opens briefly when you swallow or yawn to let air in or out and balance the pressure. When the plane climbs, cabin pressure falls, and air in your middle ear needs to escape. That usually happens easily, with a small pop. When the plane descends, cabin pressure rises, and air has to get back in. The tube does not open as easily in that direction, so descent is when ears hurt most. If pressure is not balanced, the eardrum is pushed inwards, which can feel full, muffled or painful.

How to help your ears

Swallow and yawn often, especially during the descent.
Chew gum or suck a sweet to keep swallowing.
Try a gentle pressure-equalising move: close your mouth, pinch your nose and blow very gently until you feel a pop. Do not force it.
Stay awake for landing if you can, since you swallow less when asleep.
Babies and young children often find it harder. Feeding a baby or giving a child a drink during take-off and landing can help them swallow.

When to take extra care

A cold, sinus infection, hay fever or ear infection can block the Eustachian tube and make flying painful. If you have one of these and a trip coming up, ask a pharmacist or GP for advice before you fly. See a doctor if ear pain, hearing loss or discharge continues for more than a few days after a flight. What is the strangest thing you have noticed on a flight? Tell us in the comments.