Thank you - I don't see any 0,0s in the source so I think it's something I need to take account for in the voronoi package - I'll add it to the list :)
if there aren't any 0 0 coordinate airports in the data set, maybe there are some strings that are not parsed as numbers and thus coerced to 0, a space or a non printing character (like a carriage return) can make something that looks like a number, not parse properly.
I made a small error in my explanation for the date line: I meant to say "voronoi border with the cells just to the west" (instead of east)
By the way if you have a list of the 0 0 coordinate airports, I can do a best effort search for their correct location. Let me know,