Flight query about cabin pressure

  CurlyWhirly 22:36 PM 26 Aug 12

I have never flown before but am flying to Majorca in October.

My partner (who has flown before) said that on take off I should suck a sweet to avoid a ringing sound in my ears caused by the change of air pressure.

What I can't understand is how the cabin air pressure changes as all planes are airtight ?

  Quickbeam 22:40 PM 26 Aug 12

Chewing a Curly Wurly works just as well.

  CurlyWhirly 22:41 PM 26 Aug 12

Quickbeam - yeah I love my chocolate :)

Terrified of flying though !

  Quickbeam 22:44 PM 26 Aug 12

If I can't drive there or go by train, I don't go!

  CurlyWhirly 22:48 PM 26 Aug 12

Quickbeam, that's a major restriction on your holiday plans !

  Forum Editor 22:57 PM 26 Aug 12

"What I can't understand is how the cabin air pressure changes as all planes are airtight ?"

Cabin pressure changes because an automatic system makes it happen. As an aircraft begins its climb to the cruise altitude the cabin pressure starts to rise so as to maintain a pressure of around 11lbs per square inch, which is approximately what you would feel if the aircraft was unpressurised at 7000 feet.

Your aircraft will cruise at around 30,000 feet.

When the aircraft begins its descent for landing the flight deck crew will set the cabin pressure control system to to the ground altitude at the destination airport, and the automatic system will gradually adjust the cabin pressure throughout the descent.

You are more likely to feel the effect in your ears during the descent. Some people (I'm one of them) never experience any discomfort, but others - like my wife - can get a mild earache for a few minutes. Sucking a sweet can help.

Cabin pressurisation is essential for your comfort during the flight, and is nothing to worry about. Have a good trip.

  WhiteTruckMan 23:01 PM 26 Aug 12

Aircraft are pressurised to (I think, from memory) 12000 feet above sea level. This means that when it takes off and climbs to cruising altitude the air pressure is vented until it reaches 12000 feet, then the valves close automatically and maintain that pressure as the aircraft climbs. The reverse happens on descent. when the aircraft hits 12000 feet the valves open and the air pressure increases as you go down. So any change you will feel as you ascend and descend only happens in that 12000 feet band.

The reason for this is to reduce stress on the pressurised section of the fusilage. A commercial airliner will make may flights in its lifetime. Each cycle of compression/decompression stresses the metal a tiny amount, leading to metal fatigue. The less the pressure differential between inside and out, the less fatigue on an individual cycle.

You can build an aircraft to sucessfully resist these stresses, and so maintain a sea level pressure at altitude, but that means more material, a heavier airframe, with either less payload or less fuel, giving a shorter range etc. You get my point.


  Quickbeam 23:12 PM 26 Aug 12

"that's a major restriction on your holiday plans"

Not really, I have a sister near Milan and a cousin in Rome and can visit them without flying. It would only be a problem for going to America as I can't afford the Queen Mary!

  CurlyWhirly 23:16 PM 26 Aug 12

"Cabin pressurisation is essential for your comfort during the flight and is nothing to worry about"

I had no idea that cabin pressurisation was even active on flights.

"Have a good trip"

Thank you.

  CurlyWhirly 23:20 PM 26 Aug 12

Thanks to everyone for their input much appreciated.

One final thing I'm unsure about is the difference in flight times on the departure and return flights.

Flying to Majorca is scheduled to take 3hrs 40 mins and yet returning to the UK is only scheduled to take 1 hr 40 mins meaning there's a massive difference of 2 hours !

Would this be anything to do with the jet stream ?

Just curious.

  Woolwell 23:34 PM 26 Aug 12

It's normally set at around 7,000 ft (note not metric) but has become lower on some airlines. Anything above 10,000 ft could cause altitude sickness or hypoxia. The changes in cabin pressure on generally not noticed but if you have had a cold, have sinus problems and have blocked ears then you could get some discomfort in your ears. Sucking a sweet helps but so does pinching your nose and trying to blow through it. You should feel your ears "pop". Jet aircraft are most fuel efficient at height typically at around 30-40,000 feet.

The jet stream normally affects east/west flights.

Enjoy your flight. Don't drink lots of alcohol, it dehydrates you and doesn't help. Drink plenty of water though.


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