Random Question Re: Air Traffic Control

[redsquid2]

I don't fly often, but recently I was on a flight from San Francisco to Chicago. I was in a right-side window seat, looking out. The plane banked sharply to the left, and then about two seconds later, I see a small jet pass under our right wing. I would estimate it was 1200 feet away. Is that close, or is it normal?

 

[Armithius]

1200 isn't overly close. Different size aircraft generally fly at different altitudes; sometimes with only 1000ft. of difference. It should also be noted that aircraft fly on different routes/vectors all the way that other aircraft will generally be following, so you can get near others on occasion, though ATC will generally attempt to space them apart. Problem is with thousands of aircraft in the air at any given time, airspace can get crowded on occasion, especially near major airports (and O'Hare is certainly one of the busiest) Do you happen to know what you were flying in, or what the jet that passed under you was? How close were you to your point of departure or arrival? While I'm not a pilot or a controller, I do work on the ramp at an international airport, and it's hard to work there without picking up a few things about flying.

 

[redsquid2]

Armithius, I'm guessing we were about 1 1/2 hours out of from San Francisco. The plane that passed underneath looked like a little Gulfstream-type thing. I have no idea what major cities would have been nearby. SLC? Denver?

The plane I was in must have been pretty big: three seats on each side of the aisle.

 

[Armithius]

Nah, if you were that far out from your departure you wouldn't have been low enough to be affected by any arriving or departing aircraft. It's possible the controller (or maybe even the pilot) thought that you might be a little too close to the oncoming aircraft, but chances are the bank and the passing plane were coincidental. Aircraft have been much closer than that to each other without incident. I'd imagine that you were right over a VOR, which would explain both the sharp bank (heading to the next VOR) and the close proximity of other aircraft (following a similar route.)

 

[Budgetbugout]

1,000 feet is the minimum altitude seperation for air traffic. So yes, it does happen from time to time. The sharp turn you felt is what is referred to as a vector which is a series of angled turns to direct air traffic.