Flyerstar
I have rechecked my earlier post and am sticking to my guns, and no I am not confusing GS Mini with Approach Speed. GS Mini is only one small part of the main event which is the approach speed calculation.
GS mini is only one of several approach speed protections the Airbus uses and is best thought of as the minimum groundspeed that the aircraft will be permitted to have to prevent a low energy situation. It is effectively a fixed value as long as VLS does not change which for all practical purposes it does not during an approach. Remember that the higher the tower wind, the lower is GS mini. In order for GS mini to provide meaningful protection by not permitting the aircraft speed to decay below a certain value, the value must be realistic. If you have an enormous tower wind then you will never get near that value of GSmini when the protection kicks in.
The really important issue is the approach speed and the Airbus is effectively calcluating 4 different approach speeds at any one time, 2 of which are based on GS mini. The highest of those 4 values is the one it uses and that is what is displayed on the magenta triangle the pilot sees as the approach speed target. Airbus do not formally state that, but that is what is happening.
Regarding the written explanations that Airbus give in the manuals - these are not particularly helpful as they only cover one case and do not consider such things as circling approaches for example. Without a spreadsheet or computer program of some kind which simulates the different situations that can arise using the Airbus-provided equations it is almost impossible to see what is going on. For example, what happens if there is a large tower wind and small actual wind or vice versa? What happens if you forget to activate the secondary flight plan in conditions of high wind? What happens if you put in a reciprocal wind for the tower wind? When does it not matter what wind you put in? (The answer is that for any wind of 10 kts or less, you can put in a wind from any direction and it will not affect the approach speed calculation). And so it goes on.
Coming back to my original point, if you put in a high value of tower wind on a gusty day (ie 25 kts plus) there is always a danger that you will have a significant loss of energy when that gust disappears at low level. This is because the tower wind is always assumed to be there and if it is high then you are effectively telling the aircraft to ignore everything above 15 kts. That is OK as long as the wind does not disappear, but if it does you can find yourself in a low energy situation because GSmini (which is never displayed to the pilot) is artificially low. I have seen this on a number of occasions on the 321 and it has explained a number of hard landings in gusty conditions. Once I realised what was going on, I lowered the tower wind by a few knots and the heavy landings stopped. If this all sounds wierd then just get the spreadsheet and try it yourself - you will see it really does work. Like anything else, balance is the order of the day. It would clearly not be sensible to lower the tower wind hugely because that would result in a much higher approach speed and therefore a longer landing distance plus an unacceptable float. The essence of my argument is that you should be extremely wary of puting in high tower winds (20 kts+) on a windy day.