Avionics Fundamentals was developed by the maintenance training staff of United Airlines for use as a training course for airline maintenance personnel. As such, it presents basic material which is prerequisite to category II qualification courses. Many of the explanations of elementary avionics principles found in this text are not easily discovered elsewhere. This book may be useful to anyone interested in learning the fundamentals without the design details of various devices including autopilots, flight directors, air data computers, radio altimeters, GPS, VORs, localizers, glideslopes, compasses, gyros, and indicators such as HSIs, RMIs, and FD-109s.