The paper deals with the operation of directional wireless telegraphy in aircraft where the directional aerials are installed in the aircraft.The main difficulty in this work is to deal with the errors which arise. Curves are given showing the errors obtained, and formulae are developed showing the factors on which the errors depend. Methods of predicting and correcting the errors are given.Curves of variation in bearings of transmitting stations are given and discussed. A possible cause of these variations is given.