The possibility of obtaining altitude as additional information from an airborne doppler navigation equipment is reviewed, and some of the design problems involved are discussed briefly. These relate to the form of modulation used for transmission, the aerial beam shape and the direction of the aerial beams.

It is concluded that an accuracy of ±5 per cent. ±2 ft. over the range of 10–100 ft. might be possible. The work is in an investigational stage, and no specific design is described.