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Airplane Cabin Pressure

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The holidays are here and December is a particularly busy month for the airline industry as we travel to visit family and friends across the United States.

Cabin air pressure can present problems for these travelers. The fuselage of a jet is a pressure vessel. Between every normal takeoff and landing, the cabin pressurizes and depressurizes. While cruising to their destinations, passengers need air (with oxygen) pumped into the cabin to breath. After compressing and cooling it, the engine(s) supply the breathable air. Although the altitude of a Boeing 737 will reach 41,000 feet, the passenger cabin typically attains only 8,000 feet.

Why don’t the pilots pump more air into the cabin, keeping the interior “atmosphere” near sea level? They don’t do this because the pressure differential between the thin outside air and the dense cabin air would be too great, placing excessive stress on the fuselage. As an overfilled balloon pops, a fuselage with too much cabin pressure will crack or burst open. For a B737, relief valves will open automatically to prevent the cabin differential pressure from exceeding 9.1 pounds per square inch (psi). In rare cases, due to undetected structural fatigue, fuselage skins fail even under ordinary conditions. In July a Southwest Airlines Boeing 737-300 depressurized after a one-foot hole appeared in its upper fuselage. Fortunately, the aircraft was diverted and landed safely.

More commonly, though still rare, a small hole will open in the cabin skin. Although not explosive, the hole will cause a loss of cabin pressure, and the oxygen masks to drop. After thousands of pressurization cycles, the metal can simply gives way. Fortunately, the airlines inspect their aircraft regularly, sometimes even x-raying fuselages to detect cracks. Their vigilance allows passengers to breath easily.

Associates and Bruce L. Scheiner, Personal Injury Lawyers not only has aviation experts who have a solid understanding of the complex issues surrounding aviation accidents, they are experienced pilots. Put their experience to work for you by contacting 1.800.DialBLS or www.focusedonjustice.com