Also this may be a whole other post I need to make but bonus question for anyone interested in answering: Why can I perceive the tilt(like the cabin is angled more towards the sky or is leaning to the left or right) of the airplane cabin even though I am in the same upright position in relation to the actual cabin itself?
In: Physics
Something no one else has touched on (unless I missed it) is that for some of the busiest airports, there are just too many planes trying to use the same handful of runways.
Take a look at this [screenshot](http://prntscr.com/o2lj9v). This happens to be Hartsfield-Atlanta, the busiest airport in the world… see all the light blue planes? They’re all landing at ATL.
Between flight scheduling and air traffic controllers (ATC), everything’s generally pretty smooth, but sometimes there are just too many incoming flights to get them spaced out all nice and pretty like that. There are FAA mandated minimum distances between planes, so the planes that are coming in on straight shots have to be X distance apart (if at the same altitude) or Y distance apart if more than Z feet different in altitude.
All of those planes still have to get on the ground, so there are times when, instead of a straight shot to the runway, the line of planes will have to circle the airport so that ATC can keep everyone at the mandated spacing.
Another way to think about it…. if you go to an amusement park, and you’re among the first in line for a ride, you don’t generally have to go through the whole serpentine queue, right? They’ve got a couple of chains disconnected and you can skip entire waiting areas. As the day goes on and more people enter the park, workers come by and fasten the chains, and make everyone on the outside of the chain “load up” those waiting areas, right?
Same deal. If ATC can have planes speed up or slow down to keep the spacing right, generally they’ll try to get all the planes (from one direction) to just make a longer straight line, and everyone shoots a straight approach. One guy’s coming in from Miami (or somewhere else), ATC will have everyone behind a specific flight slow down a little and get that Miami flight in the middle. Too many planes, they open the queuing areas with TV’s showing cartoons, and everyone circles around the airport, from the top down.
Here are a couple of images that might help clarify, in case I’ve muddied the water too much…
[Separate stacks](https://www.heathrow.com/file_source/HeathrowNoise/Images/Heathrowoperations/stacking590.gif)
[Conventional vs. linear holding patterns](https://www.heathrow.com/file_source/HeathrowNoise/Images/Heathrowoperations/stacking590.gif)
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