The pattern of a magnetic anomaly varies with the dip of the inducing field. For an aeromagnetic survey intended to discover induced dipole sources, the best flight direction is defined as the one offered maximum target width by an anomaly. This direction may depend on the amplitude of the anomaly. A method is proposed for estimating efficiency of direction for a range of anomaly amplitudes.The efficiencies of lines bearing north, northeast, and east are compared. At the equator, lines bearing north are twice as efficient as lines bearing east. With increasing inclination, the advantage of lines bearing north disappears at dips of about 20 degrees. Lines bearing northeast are chosen for dips between 20 and 70 degrees. Flight direction is unimportant for dips greater than 70 degrees.