Why is it a necessary precaution on commerical airplanes to have oxygen masks for every passenger?

Question

I need to find this question out for an assignment in class thats due tomorrow!!!

also another question,

If you lived on the west coast of South America, from which direction would the wind usually blow.


And the last question is,

The northeastern United States tends to have colder winters than the nortwestern United States. Which winds contribute to this difference.?

Answer 1

Anyway, while I'm sure you know the basics of pressurizing an aircraft, I'll run through it real quick. Pressurization is purely a matter of pumping air into the cabin and then metering it's release in order to maintain a cabin altitude that humans can function at. The air coming in is supplied by the engines and is routed from there to the air conditioning packs and then into the cabin itself through supply ducting. The metering of that air is done by the cabin pressurization controller through the 'outflow valve'. A properly working pressurization system will maintain the 'cabin' altitude well below the 'actual' altitude of the plane. When the BA 747 lost all it's engines, they lost the supply of cabin air to maintain pressurization. Once that happens, the cabin altitude will start to climb. It doesn't happen immediately, because the outflow valve was likely closed....but the cabin altitude will definitely climb towards the plane's current altitude.

There are a number of FARs that deal with Pressurization and Supplemental Oxygen systems. We'll start with FAR 25.841 which requires that pressurization systems in commercial aircraft must maintain the cabin at no higher than 8000 ft. In other words, when the plane is at it's max altitude, say FL410, it must maintain the cabin altitude at no more than 8000 ft. I can tell you that for most planes at normal cruise altitudes, the cabin is likely in the vicinity of 7000-8000 ft. The next set of FARs can be found in part 121.329-333. This delineates when oxygen must be used and how much you need to have on board for the passengers and crew. Specifically, the crewmembers must be on oxygen whenever the cabin altitude exceeds 10000 ft. Therefore, the warning on the cabin altimeter is generally set at 10000....it's a warning to the crew to put their O2 masks on.

The rules for passenger oxygen supply are somewhat less restrictive and have several different altitudes that lay out exactly how much oxygen must be on board and who must use it. However, FAR 25.1447 says that any cabin oxygen system must deploy automatically prior to 15000 ft. All of the planes I've ever been on have it deploy at 14000. The crew can also manually deploy the masks anytime they choose, but if they mess up the pressurization, the mask will automatically drop at 14k as a testament to their error.

Going back to the BA 747 crew. They are flying along at cruise fat, dumb, and happy. The cabin altitude is likely in the vicinity of 7000 ft. They lose all engines and therefore their pressurization supply. They cabin altitude starts climbing. Even if they start a descent, the cabin will continue to climb. Eventually it will pass 10000 ft at which time the cockpit warning horn goes off and the crew must don their O2 masks. According to your summary, the 'cabin' altitude reached 10000 ft as the plane was passing 26000 ft (as I recall, at this point in the emergency, one of the crew members had trouble with their mask meaning they had to descend faster and lose precious altitude that they needed to restart the engines). The cabin continues to climb and eventually hits 14000 ft. Now the passenger masks automatically deploy. At some point, the cabin altitude will reach the actual altitude of the plane and then they will both descend together as the plane loses altitude. The key here is to recognize the difference between cabin altitude and actual altitude....they are rarely the same unless the plane is completely unpressurized.



heres an idea for the oxygen mask

You know why they have oxygen masks
on planes?

JACK
No, supply oxygen?

TYLER
Oxygen gets you high. In a
catastrophic emergency, we're taking
giant, panicked breaths...

Tyler grabs a safety instruction CARD from the seatback,
hands it to Jack.

TYLER
Suddenly, we become euphoic and
docile. We accept our fate.

Tyler points to passive faces on the drawn figures.

TYLER
Emergency water landing, 600 miles
per hour. Blank faces -- calm as
Hindu cows.

from fight club


an air safety expert explains what happens inside an airplane that decompresses and what passengers need to do when an airplane's oxygen masks fall from the ceiling.

Guest:
thats the second link

Answer 2

OK, about your airplane question: I think if there was a problem with oxygen, everyone would want to be able to breathe. If you don't have a mask for everyone, someone will not be able to breathe.

I don't know about the other questions, though.

Answer 3

CHEVYTRUCKDOOD IS A NERD!!!