TL;DR: I encountered several bugs when I tried to relocate a charlie. Game will crash now if I try to get rid of that helicopter.
First created EU base then created NA base. Had 2 Charlies in EU and wanted to relocate 1 Charlie to my new NA base with veteran soldiers. After a ground combat with said soldiers I wanted them to relocate at the nearby NA base rather than return to EU.
So the Charlie was in flight back to EU. I was able to use the relocate for the Charlie while it was still flying back. On the overview map it immediately moved to the EU base from overview map and started flying to NA base. I believe the soldiers were moved EU immediately but did not relocate even though they still were bound the that Charlie which is probably a bug. I relocated them separately.
Once the charlie and soldiers arrived at NA, I was unable to assign the soldiers to that Charlie. Also that Charlie did not seem to ever arrive at its destination and never took up space at a hanger even when it was at its final destination.
I was never able to decommission it since it says it was currently in flight even when it was not. Also if I sent it to combat to be destroyed by a UFO it would cause the game to crash shortly afterword.