Hi. In the air modules you need to specify the address of the ground module in the fields Destination address low and destination address high. This will make the air modules send messages to the ground.
Then in the ground module you need to put destination high=0 and destination low=FFFF
This will make the ground module send messages to all other modules and hopefully the corresponding air module will receive it.
I believe these modules will act as routers so if a message is received by one aircraft it can then be forwarded to the other aircraft even if the second one is out of range from the gound module.