How do you get a common track for all the RIVET arrivals into Sydney? They have to converge somewhere......
Different types, different weights, different companies - all perform differently even when the aircraft is doing it. An AIrbus heavy will often be 10,000ft lower than a 737 at 100 miles. Sorry, it's all wonderful when you're the only aircraft in your bit of the sky but it doesn't work so well when you're not. We have to separate you the whole time, not just at the feeder fix. That's why you can't just do your own thing.