Suppose you were a pilot for an airline for five years. But then you left the job. So if someone asks you "do you know how to fly a plane?" what would your answer be?
a) I have been a pilot for five years so i think i know how to fly a plane
b) I had been a pilot for five years so i think i know how to fly a plane.
As far as I know it should be "b" because he is not a pilot anymore and if I say "I have been a pilot", it can also mean that he is still a pilot. But I don't wanna say that because he isn't.