Airborne Radar - avoidance distance & WX vs. MAP

[Virtus]

Doing a bit of a search I didn't really find what I was looking for.

1) What distance should you avoid thunderstorms (red or magenta returns) that are painted on the radar? I remember Archie Trammell said that if a return is magenta in the centre, then the entire storm (out to the green return) should be considered as being magenta. Makes sense then that you should be 20 NM from the green return...

2) The radar I'm using (Bendix/King RDR-2000) has a ground mapping mode. The gain function only works for the ground mapping mode and not the weather mode. Why wouldn't the weather mode allow the use of adjustable gain?

3) What is the difference between ground mapping mode and weather mode?

4) It obviously seems important that you should be in weather mode instead of ground mapping mode when avoiding thunderstorms but what exactly is the reason you should be in weather mode? It would seem beneficial to have the gain feature so that you could determine how much above the red or magenta threshold the returns actually are.

Thanks for the help!

[bubbers44]

When you get in heavy precip us old timers ran the gain down to not make the whole screen red making the display meaningless. One time going into Dallas we had all red and were in the middle of about 20 airliners on downwind doing the same thing. No one in front was having a problem, so against my better judgement we continued with no problem. If I was the only airplane I would'nt have done it. I am not saying my decision was right but all 20 landed with no problem.

[PEI_3721]

A cumulonimbus should be cleared by 20nm upwind at least. (http://sapilot.com/a320/otherfile/Ops_In_ICE_CON..ppsx) – Airbus recommendation re ice crystals - last slide.

Weather Radar (http://sapilot.com/a320/otherfile/WX.pdf). (http://sapilot.com/a320/otherfile/WX.pdf)