system
Given the following post, respond as if you're commenting on Reddit:
human
If planes are pressurized why do we have our ears popping?

I mean, there is supposed to be a constant pressure in the plane and the pressure is supposed to be independant of the outside pressure, so why do we have our ears popping when the plane is gaining altitude?
gpt
Aircraft *don’t* maintain constant ground level pressure in their cabins. They’re required by law to maintain a *minimum* pressure, which is equivalent to the pressure at an altitude of 8,000 feet. So when a plane takes off, the pressure in the cabin falls until it reaches the minimum required by law, and then remains at that level for the duration of the flight. When it lands, the pressure increases until it matches ground level. So your ears may pop on take-off and landing.

The reason is cost. A pressurized cabin must hold in high pressure air at cruising altitude, and the greater the pressure differential between the inside and outside, the stronger the cabin must be. Strength requires more material, adding weight and reducing fuel efficiency. At sea level, the pressure is 14.7 psi, while at 8,000 feet the pressure is 10.9 psi, for a difference of 3.8 psi. So if the cabin maintained sea level pressure, it would need to withstand an extra 3.8 pounds for every square inch of surface area, making it heavier.

The FAA determined that 8,000 feet is a good compromise that the vast majority of people find comfortable. Even if you’re sick, it won’t kill you unless you have something like pneumothorax, in which case you shouldn’t be flying anyway. So they settled on that number. But the majority of aircraft manufacturers do better. The Boeing 767 maintains at least 6,900 feet of pressure, the Airbus A380 averages around 6,100 feet, while the Boeing 747-400 won’t let it drop below 5,200 feet. So your subjective impression of ear popping may vary based on which plane you’re in. It’ll also vary depending on where you take off or land. If you’re taking off from sea level, the drop from zero to 8,000 feet is substantial, and you’re going to feel it. If you take off from Denver, you’re already at 5,200 feet, so you may feel no change at all, or a very small change.

There are business jets that can maintain sea level pressure all the way, like the Emivest SJ30. They don’t care as much about per-seat passenger costs, so they’re willing to spend a little extra on reinforcing the cabin for passenger comfort. But big commercial airliners are designed with compromises between comfort and cost, and not having sea level pressure is one of those compromises.