Questions about visual separation
 

Hey there,
I'm trying to understand the method of visual separation for arrivals and departures. Unfortunately, with the help of the official guidelines, I don't really get in. Maybe you can give me some hints. I have some questions, some of them might sound a little confusing:

- Under what conditions (just VMC?) visual separation might be applied? Is it the usual case to use it in good weather?

- Is there a minimum separation between two arrivals/departures using visual separation (except the consideration of the runway occupancy times)? In the case of visual separation, radar and wake turbulance separation don't have to be maintained?

- I have a pretty special question about a concrete example: I read the survey dealing about the expansion of Airport Frankfurt some years ago. There they assumed vortex separation in the crossing point of the flight path of an arrival on RWY 07R and a following departure on RWY 18. Does visual separation has any influence on this separation? Or does it just affect the separation between two aircrafts on the same runway?

Many thanks!

1.) VMC or not; usually the crew will request a visual approach when the runway is "clearly" visible, and with ground contact accordingly (some "home" pilots occasionally overrule this), and EU-OPS require RVR800m or more (Visual approach. An operator shall not use an RVR of less than 800m for a visual approach.)

2.) a quick copy-paste from Doc. 4444, Chapter 6.,

6.5.3.5
For successive visual approaches, radar or non-radar separation shall be maintained until the pilot of a succeeding aircraft reports having the preceding aircraft in sight. The aircraft shall then be instructed to follow and maintain own separation from the preceding aircraft. When both aircraft are of a heavy wake turbulence category, or the preceding aircraft is of a heavier wake turbulence category than the following, and the distance between the aircraft is less than the appropriate wake turbulence minimum, the controller
shall issue a caution of possible wake turbulence. The pilot-in-command of the aircraft concerned shall be responsible for ensuring that the spacing from a preceding aircraft of a heavier wake turbulence category is acceptable. If it is determined that additional spacing is required, the flight crew shall inform the
ATC unit accordingly, stating their requirements.