Given the helicopter industry is a very hard one to make a career in, and you need to maximise your chances of getting a job, I would err on the side of being conservative and avoid a tattoo.
Imagine you went for a job as a VIP pilot, and the Chief Pilot had to choose between someone with tattoos, and someone without. He might think "do I want VIP customers to see a pilot with tattoos? Mmmm.. I better not take the risk".
I know it shoudn't matter, and the way pilots dress shouldn't matter either, but you always see pilots dressed in the "uniform" of black trousers, white shirt, gold bars etc, as that is what customers expect professional pilots to look like.
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