Posted by: harrisonjones | April 15, 2011

What if the roof blows off?

Can you imagine sitting in a Boeing Fluf (fat little ugly football) at 35,000 feet and watching your complimentary peanuts fly out the roof? If you’re an aviation expert, read on and add to the discussion. If you’re just a normal passenger, who ignored the safety briefing, maybe I can offer some insight and generate some questions. 

Why are airplanes pressurized?

We, as human beings, need oxygen as well as the complimentary peanuts to survive.  The percentage of oxygen in the atmosphere at 40,000 feet is the same as it is at sea level, however we require a level of barometric pressure to force oxygen into our lungs to be processed and that pressure does not exist at altitude. Barometric pressure is what the weather person reports on the 6 o’clock news every night and we usually ignore. That pressure normally equals about 15 pounds per square inch at sea level. Didn’t realize that you were carrying around 15 pounds of air on each square inch of your body? No problem we’ve adapted to it. The weather person expresses it in inches of mercury and the norm is 29.92 at sea level. Enough technical stuff already, back to the problem. When the airplane goes up, the atmospheric pressure goes down and we just can’t live without it. 

How does it work?

As one of my instructors used to say when asked that question, “Works good, last a long time and is easily cleaned with a damp cloth.” The problem is solved by pumping compressed air into the cabin to maintain the pressure. Where do we get the compressed air? No problem, the jet engine draws air in (Humans too if you get too close) and compresses it, mixes it with fuel, ignites it and the heat expands it and forces it out the tailpipe. The process is summed up in four words for pilots. Suck, squeeze, burn and blow. Works good, last a long…  We just bleed some of the air off the compressor section; pipe it through an air conditioner and out the little outlet above your seat. The system provides about 8.5 pounds per square inch at cruise altitude and the cabin altitude remains at 8000 feet or less. 

Now what happens if the roof splits open?

All our compressed air goes out the hole like a busted balloon and takes our peanuts with it. Somewhere it’s raining peanuts. Now you’re living in the rubber jungle. When the cabin altitude exceeds 10,000 feet, all the oxygen masks fall from the ceiling and hang there on rubber tubing. A point worth remembering! The safety briefing encouraged you to pull the mask to the full extension of the tubing before placing it on your face. That’s because the tubing has a string attached to it and when you pull the string it trips a switch to activate the chemical oxygen generator above your seat. There’s one unit for each row of seats and one extra mask in each location in case a child is riding in their mother’s lap. Two kid’s in one row? Bad juju. Just hope you have a sharp flight attendant who moves one of them before takeoff. Place the mask over your nose and mouth and breathe normally. That’s what the doctor said right before he removed my appendix. The oxygen is continuous flow and under pressure to force it into your lungs. It will last 10 to 15 minutes. 

Now what?

Enjoy the oxygen and tighten your seat belt, you are about to be transported to 10,000 feet very rapidly. The captain is required to execute the emergency descent without reference to a written checklist. Don the oxygen mask, retard the throttles, extend the speed brakes and lower the nose until the airspeed is on the little red line on the indicator. Pray that there’s not a thunderstorm or a mountain below you. (Save that for another blog) Keep your elbows out of the aisle because if the beverage cart is in use it will be headed for the front of the airplane very quickly. You might watch for flying laptops and other missiles also. 

I’m new at this and I realize it’s too long and too technical, but I’ll work on it. See you next time.  

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