FUTABA FX40 Instruction Manual page 32

Teacher mode
"NORM" mode (Normal mode);
"MIX" mode;
Student mode
<System Menu>
32
"FUNC" mode (Function mode);
[Notes]
1. In the teacher mode, the trainer function
display does not come on as long as the
student's transmitter is not receiving signals
from the teacher's transmitter (when the
student's transmitter is not connected).