Hey, I work around alot of Cessnas and I've noticed that on the 172, the fuel tank air vent is a little pipe hanging under the wing on the pilot's left side. On the right side the vent is built into the fuel cap. Why are these two different? I know it's for air to get into the tanks to take the plce of the used fuel, but why aren't the vents the same on both sides? Wouldn't that make more sense? What about airliners? Are they built into the cap or is there a different system?