You may try to incorportate one of the following two things:
1 - Check that plane/chopper being refuelled is at the back of the tanker and a bit lower, not more than 10m. Then check that distance to tanker is kept (-+ 10m in horizontal and vertical) for 5 seconds, then you add a refuel action to the player. Once the player activates the action check that player's vehicle still keeps the distance while loading fuel.
2 - Once the player's vehicle is close enough, you simply add the refuel action to player's vehicle. When player activates it, the tanker starts to generate particles with a lifetime of 3 seconds, 0.5m sized, with some weight (the particles goes slight down, and pretty few rubber), A refuelling gamelogic is created too, you set an end-of-life script for every particle. That script just setPos the refuelling gamelogic at the end position of the particle when it dies (when particle dissapears that script will get the last position of the particle), now you check distance between player's vehicle and refuelling logic (instead of tanker). The "hose" of particles will represent the refuelling hose, the tail of that "hose" is everytime the last particle dissapearing and executing the script that will place there the refuelling gamelogic. So, as the tanker moves, the hose moves following tanker's path. Depending on tanker's type you may generate the hose starting from wings, or body, or even more than one hose (one comming out of each wing, etc).