Dialog action and waypoint distance

Hi to all! I need to put in a mission a dialog action with a sound that start at some miles from a specific waypoint (Vor or Ndb or fix). Can you tell me if in the mission object tool exist a specific istruction (for example as the old Fs2002 language : if (fix coordinates) < 20mn then play x.wav) ??? Now i have created a mission that start on air, after 5 seconds start a first wav, then at about 20 miles from a vor would be start a second wav...please, help me! There is a conditional trigger or an area/volume trigger for this??Thanks in advance Patrizio