I have purchased your ebook which I have found most useful – thank you. I just have a couple more queries if you wouldn't mind advising me.
One of my anxieties relates to the aircraft losing cabin pressure. I have read that this seems to be more serious a problem when this happens slowly rather than suddenly as people don’t realise it’s happening and lose consciousness before they can do anything. I’m also worried that it could get very cold/very hot causing people to lose consciousness.
Associated with this worry is the concern that if something like this happened, the oxygen masks would not work/would be affected by this problem.
Is there anything you can tell me about this issue that might reassure me?
Many thanks in advance.
Hi there Jane,
The plane is pressurised to about 8psi or 8000 ft when you are actually at 35000 ft. This is very comfortable even for older or infirm people. The air is pumped in by the engines and exhausted through a valve (outflow valve) at the rear of the plane. This valve modulates (regulates) to keep the air pressure just right.
What can go wrong? The valve can have a fault but there is a backup system. If that fails the pilot can do it manually. A window could possibly (very rare) blow out. A door could possibly leak around the edges. In the case of Helios Airlines, the badly trained pilots did not turn on the air. No matter what the cause, the pilots can usually fix it right away by switch selections. If that fails they do an Emergency Descent to 10,000 ft in about three minutes. In the cabin the oxygen masks deploy and these will keep you breathing happily until the plane levels off at lower breathable altitude.
Now to your question: There are two kinds of decompression; 1/ Slow and subtle 2/Explosive. The first is the one you refer to and might be caused by a variety of reasons. But since Helios, all planes have extra warnings that sound off if the cabin goes above 10,000 ft cabin altitude. There is an automated voice that calls out, and a light that illuminates. Then at 14000 ft a horn sounds off. So it is now impossible to ignore the subtle cabin pressure loss. Also pilots now undergo training in this procedure pretty well every year. The explosive one, which is very rare indeed, is when something much worse causes a hole in the plane and the air is lost suddenly. In the event that the pilots cannot control cabin pressure, they descend as described earlier to a safe altitude where everyone can breath normally. The masks are deployed by the pilots using a switch, but if that were not to happen, they are deployed automatically at 14000 ft cabin altitude. The temperature would fall, not rise, since the air that allows you to breath and keeps you nice and warm may be lost. But since it only takes a couple of minutes to get down to 10,000 ft this is never an issue and the cabin would remain reasonably warm - a bit like turning off your house heating in winter - it takes time to cool down. Lastly, this is a very rare event for which pilots are very well trained. Like every thing in aviation, lessons have been learned and new procedures brought in. I flew in BA for 34 years with 3500 other pilots and I can only remember one Emergency Descent in all that time, over Delhi. Nobody was injured. A funny story comes back; the passengers were mainly Indian and did not understand the safety briefing. When the masks came down their ears hurt due to pressure loss so they put the masks over their ears! Even so nobody was hurt and the plane landed safely. There is an answer to everything that occurs on airplanes and nothing is left to chance. A well-maintained plane flown by good pilots is safer than any other form of activity by a huge margin. Sleeping is far more dangerous, as are bee stings and especially driving a car, which is thousands of times more dangerous. If there is anything else you need to know just email right away Jane.
Thank you very much for your comprehensive reply which was very reassuring. I am feeling much more confident about my upcoming flight.
I would be happy for you to put my question on your blog.
Many thanks again.