Hopefully this won't degenrate into another GLA v PIK thread! Anyhow, there were definitely restrictions on transatlantic flights from GLA after airlines moved from PIK in the early 90s. I distinctly remember my honeymoon flight from GLA to Boston just after NW had moved from PIK. While sitting awaiting push back the pilot announced that 'due to the length of Glasgow's runway and the atmospheric conditions, I can either leave 40 passengers behind or fuel stop at Shannon...' We fuel stopped at Shannon!