Berlin - Most air travellers are aware that cabin pressure in a plane is artificially elevated so passengers and crew can feel comfortable.
The air pressure outside when a plane reaches its cruising height is too low, making the air cold and thin.
During the flight, most passengers feel more or less normal - but exactly what level of air pressure is there in a plane? The answer may come as a surprise. It's not the altitude you would usually experience on the ground that is being replicated.
It's actually more similar to what you'd experience at the top of a high mountain.
The plane's cabin pressurisation system generates what is standard at an altitude of around 2 500 metres above sea level.
The plane is constantly exposed to a difference in pressure between inside and outside the plane during a flight. Outside there is a continuous drop from being on the ground to the plane reaching cruising height. That places strain on the fuselage.
It’s important that changes be gradual and be monitored, to make absolutely sure that the fuselage doesn't rupture.
The classic blocked-ear feeling that passengers experience during their flight is actually dependent on the location of the airport the flight takes off from. The lower the altitude of the starting point, the more severe the ear pain can be, since passengers are affected by a greater drop until mountain-top pressure is achieved.
So, for example, when a plane takes off from Berlin's Tegel airport in Germany, which is around 40 metres above sea level, the amount of pressure that needs to be generated in the cabin is substantially higher than during a take-off from Mexico City, which is around 2 200 metres above sea level.
In the latter case, the ears of most passengers don't pop, as there is less to compensate for – simply put, the pressure hardly drops much to become equivalent to the standard altitude of around 2 500 metres.