BA doesn't like visible tattoss. That said I know several pilots working for them who have tattoos. My advice is use Derma Color medical standard concealer. I was given some by a plastic surgery nurse and it covers up a 14 inch long scar a treat. You can order it at the counter at bigger Boots but you're better off paying a scar clinic to show you how to apply it and get the right colour. I promise they won't be able to see a thing.