Mutt,
I can't speak to the European requirements, but on the presumption that this aspect of the JARs will echo the FARs, the following observations probably are relevant to the original post's question. I suspect that the JAA system is somewhat similar (except that I vaguely recall several BCAR AFM definitions including a reference to 7 knots as suggested in the previous post).
(a) the rules as they are written present two problems
(i) one has to get the correct issue for a particular Type/model to have any chance of getting the story.
Even then it may not be encompassing.
(ii) the rules as written, as they may be interpreted by the lay reader, may have little to do
with the interpretation imposed by the certification process. In particular, much of the detail
is not included in the rules as published.
(b) in respect of (ii), interpretation of the rules will be dictated by one or more of the following
(i) what the judge says after the accident enquiry
(ii) what the manufacturer negotiates with the certificating regulatory authority
(iii) what the regulator prescribes in advisory data - which is where we usually go to find out
something about what the regulator intends us to think what the rules might mean
In the case of the FAA, the useful explanatory data appears in Advisory Circulars, Orders, and the like.
In respect of Vmcg, a useful document is AC 25-7A which is the Flight Test Guide for heavy aircraft.
Unfortunately, I have to hand only the superseded -7 issue so there may be some change in the detail - although I would not expect too much substantive alteration in respect of Vmcg.
Ignoring some of the niceties,
(i) the preamble suggests a maximum wind for testing of 5 knots (preferred) and 10 knots (maximum).
(ii) the bit dealing with Vmcg indicates that the data is determined or reduced to zero wind conditions. What actually happened for a given model would be buried in the certification data.
This now ought to prompt a very pertinent question. What happens in the OEI case in a crosswind ?
Australia, if I am correct - and I may well not be, is the only country which experimented much with looking at real world operationally rational handling problems on the runway as a part of its consideration of appropriate runway widths some years ago.
During some of these flight tested programs, it became apparent that the situation with a min V1 failure at aft cg and much of a crosswind could present some nasty surprises for the unwary pilot.
Of direct relevance is the rate at which centreline deviation increases in the min V1 region under OEI conditions - this is quite alarming to any pilot who prefers boring flights and interesting overnights. In particular, crosswind from the "wrong" side has the effect of increasing the "real" Vmcg above the published figure. For one program, the manufacturer provided proprietary data for the relevant aircraft model which indicated that the increase in Vmcg with crosswind was approximately one half knot/knot and I presume that this sort of figure is likely to be typical. Thus, for a min V1 scheduled takeoff in significant crosswind conditions and with an aft cg, the aircraft is at very real risk of lateral runway departure in OEI conditions.
If you doubt this statement, try it in your simulator. Unless the sim is not programmed appropriately for this situation, you might have cause to reassess your doubt. For the program with which I am presently involved, towards the end of the endorsement sequences I give the students just such a scenario. In almost all cases, the result is a very convincing lateral departure from the runway ... along with two very wide pairs of eyes and two stunned expressions.
In the situation of takeoff from a short runway at low weight, you don't have too much in the way of options - either you
(a) delay until the crosswind abates, or you
(b) accept the risk, smug in the knowledge that you will die in some sort of legally acceptable way, I guess.
In the situation of a ferry flight, or similarly low weight operation, from a longish runway, there are, at the very least, two options -
(a) blindly use the normally scheduled min V1 data, or
(b) if such a procedure be not proscribed in your company ops manual, consider using the speed data for a higher weight, being within the applicable RTOW range for the conditions. How much higher ? I like the idea of looking to a weight which gives an increase in V1 of around half the crosswind if the cg is near the aft limit and somewhat less if the cg is further forward.
Food for thought ?