Hopefully, we never need an aircraft to be fully grounded with a tethered cable. That'd be ridiculous. As a kid, I had a plane that was tethered and would only fly in circles. Oh, where the mind wanders on a Friday
Its standard to ground out a helicopter carrying a sling load before the load is touched/handled (it may even have a longer grounding cable that drags across the ground as it descends) because it can gather some pretty dangerous levels of charge.
Speaking of grounding a helicopter, it reminded me of the Hunt For Red October scene of trying to get a person from a helicopter to a submarine. It always seemed like such a complicated something as opposed to just putting someone in the water to let a diver collect them, which is precisely what wound up happening anyways