The typical route seems to be a flight to Poland and then.....well, it's something like an 8 hour train journey to Kiev and the Russians have taken to bombing the rail network to stop the transport of weapons. Or folk can fly from Poland to Kiev but that would require a fair bit of liaison with the Russians, pilots willing to take the risk and trust that the Ukrainians will not use such a flight to create an 'incident'. Bono might naively trust his hosts - I doubt the Poles do.