I don't recall ever having my drone that close to a manned aircraft. I would be concerned that if a helicopter saw your drone and it was "too close" they would report it and then for sure the FAA would want to speak to you. So far I haven't had...
I estimate I was at least 200m below the chopper as it flew over. I had to switch to the telephoto lens to get the footage. It arrived so quickly I wouldn't have had time to land anyway so for me the best course of action was to decend to a safe...