In these days of long distance flights across large stretches of ocean aeroplanes will make considerable use of radio direction-finding apparatus, enabling them to keep their course on to a transmitting station at their goal. Over the Atlantic, for example, a series of beacons all the way across would be quite impracticable. The following is an analysis of the course flown by an aeroplane under these circumstances, showing also the increase in flying time over that on a compass course, and also the maximum deviation from the compass course.