I've been trying to think through how it would determine longitude based on rotation of the earth and I agree, that's not really possible. I wonder what other tricks it uses to find the initial location.
walden
joined 2 days ago
This sounds pretty fancy.
Commercial aircraft get their location from multiple places including GPS, ground based facilities (VOR's), IRS, etc. IRS is what I'm used to calling it, but it's the same as INS, which is what this article is talking about.
It determines location by keeping track of rotation, acceleration, etc. It's often called "dead reckoning" because it just gives the best guess, and you don't know how accurate it is. There are multiple of these devices on each aircraft, and they compare their locations to the other sources and if one is drifting way further than the rest, it gets ignored. That's a very basic explanation because how it really works is way above my knowledge level.
It's very cool how these devices find their location, though. When you first boot the system up, it spends about 5 minutes measuring the rotation of the Earth. For this reason, you can't reset it when in motion. Based on what it feels it can determine your exact location on the surface of the earth.
It's recommended to not begin boarding until it's finished, but one person moving around, gusts of wind, etc. don't bother it.