The Phantom may enter "Failsafe" if no control inputs are received for a period of 20 seconds.

I fly an FC40 and in the manual, on page 17 it states:
"Note: if you start the motors, but do not push the throttle to take-off the aircraft, in this case it is very dangerous to turn off the transmitter, because the aircraft will take
off automatically, so do not try this."

Here's a big NO NO........  IDLING.