Why do my ears pop during a flight, even though the aircraft is artificially pressurised

A.� Because the pressure in the aircraft is reduced gradually to a safe level, rather than achieved in one go. So your ears pop as they respond to this gradual change.

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Q.� What is the highest altitude at which humans can live

A.� Around 5,000 metres is the highest altitude you could live for any period of time. However, subsonic airplanes fly at 12,000 metres, an optimum height for fuel economy.

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At 12,000 metres the air pressure is only around one fifth of what it is at sea level.

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Q.� What would happen if sea level pressure was maintained at 12,000 metres

A.� The pressure inside the plane would be so great in relation to that outside that the plane would explode.

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The air pressure inside the plane is, therefore, maintained at the safest level, that of around 2,5000 metres, when the plane is cruising. Even so, anyone with respiratory problems or who has been drinking alcohol while flying may still feel ill at this reduced pressure.

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Q.� What happens when taking off from airports at high altitudes

A.� Some airports, notably La Paz in Bolivia, which is 5,000 metres above sea level, have a much lower outside air pressure than is safe. In this case the pilot actually has to gradually increase pressure on take off or decrease it on landing at La Paz.

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Q.� What can I do if my ears don't pop

A.� By the time you land the pressure on the outside should be the same as that on the inside and the pressure on either side of your ears should be equal If not, pinch your nose gently and blow to increase the pressure in your head slightly, which will pop your ears.

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Alternatively you could, finances permitting, switch to flying Concorde when it comes back into service. Because of the high altitudes it flies at the�fuselage has to be extra strong and so the internal pressure does not have to be lowered as much as it does for subsonic planes.

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Do you want to know why something happens the way it does Click here to ask.

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by Lisa Cardy