I was wondering why sometimes a flight from London to Mexico City will go more south kinda over the Azores Islands and then down across Florida to MMMX, instead of the normal route over Canada then down through the central U.S?
Recently? The volcano has shut down the Atlantic from Iceland to Northern Spain so it may be shorter to go south rather than due north then west to cross north of Iceland.
Otherwise winds aloft or failure to pay NavCanada fees.
John in Saudi
Okay, thanks… And they would fly that route even before the volcano… 
In that case winds aloft sometimes do weird things.