14th
Air Pressure Changes in Airplane Cabins
Whenever I travel, I have the hardest time getting my ears to pop when I want them to. The discomfort isn’t too bad, but all the babies on the plane don’t seem to enjoy the non-ear-popping experience too much either…. So I was wondering what the actual pressure difference (or rate of change) was that causes ear-popping sensations. At sea level, the air pressure is about 14.7 psi. According to the first patent that I found on Google about airplane cabin pressure, the minimum pressure for human comfort is about 10.92 psi (which corresponds to an elevation of about 8,000 ft). Apparently, cabin pressure systems try to keep the air pressure greater than 10.92 psi when the outside air pressure at 45,000 feet is actually around 2.14 psi. Since I’ve experienced my ears pop driving between San Jose and Tahoe before, I’m estimating that my ears can pop when I experience a pressure drop of less than 1 psi — given that the the barometric pressure for San Jose is usually near 14.6 psi and Tahoe’s barometric pressure seems to be near 14.4 psi today. And that 1 psi change (when I’m driving) happens over the span of a couple hours or so. These air pressure differences don’t seem that large — which may explain why airlines can’t eliminate the ear-popping feeling in their planes. Wikipedia’s entry on cabin pressure states that airlines don’t maintain cabin pressure at 14.7 psi because it uses too much fuel and it stresses the fuselage. Maybe next time I fly, I’ll bring try to bring a barometer of some kind….. ADDED NOTE: I found a table of elevation to air pressure which seems like handy data.
