I live on Montrose Avenue in Chicago, about 5/6 miles east of ORD and nearly parallel to runway 90L. As I see the many planes approaching so evenly spaced I wonder how the controllers/pilots maintain such even spacing, i.e., 3 miles, 1". How is that spacing controlled.
I am an old Air Force vet, an airplane fanatic, but not a pilot.
Thanks for replying.

Simply put: Practice. They can measure the distances via their radar scope, but it mostly comes down to knowing what looks right.

lots and lots of speed restrictions, along with some fancy vectoring, and if they’re lucky some visual separation on the arrivals.

Speed control is the primary means. Aircraft are assigned specific approach speeds to maintain so that everyone is moving at roughly the same speed or speeding up/slowing to keep the spacing tight. 3 miles of separation is the minimum but to use more than that especially at a busy airport like KORD wastes airspace and results in reduced arrival rates so ATC works very hard to keep the spacing at those nice even distances.

Roger Curtiss

well…after many years of rigorous training, pilots are accustomed to heavy traffic on approach…o asked this question to a BWIA pilot from here in Trinidad and he said that it’s mainly practice and also, one must be extremely cautious when approaching in busy aiports such as JFK where he flies to…he says it’s just a matter of timing and falling into the approach pattern of the respective runway!
hope it helps…

trini69! 8)