Originally Posted by
LarryJ
In the case of transport-category airplanes (airliners), the previous flight must be clear of the runway (all of it past the yellow double-solid/double-dashed lines) before the next airplane crosses the runway threshold. If that's not going to happen then the controller sends the second airplane around.
Not exactly correct. The previous arrival just has to be past the white runway edge line, IF there is nothing to hinder him continuing across the hold short line (the yellow lines.)
Also, to answer the minimum safe distance situation, if there is a departure ahead of the arriving aircraft, the departure has to be 6,000 ft down the runway and airborne before the arrival crosses the threshold.
If you are sent around, I'd say most of the time it's the arrival/departure situation, either due the departure being slow to start take-off (most of the time) or the controller misjudging the gap. The arrival/arrival situation is less common, but tends to happen more on arrival only runways, where the approach controller can vector aircraft closer together. Then, every once in a while, there is a go-around either due to the pilot coming in too high or too fast, or some problem with the aircraft.