Abstract: An aircraft instrument landing system for use on an aircraft runway to guide approaching aircraft along a glide path comprising in combination first and second directional transmitters to be disposed on the left and right sides of a runway for transmitting radio signals which will overlap including a high frequency oscillator complex for supplying a high frequency output carrier signal from each transmitter and modulator means for each transmitter supplying a pair of different identifiable modulation signals for each transmitter. Each transmitter defines a "reference plane" which is inclined to the horizontal in such a manner that the intersection of the two reference planes defines a desired glide path.