The first two parts of this series of articles on the Microwave Landing System (MLS) which will eventually replace the Instrument Landing System (ILS) appeared in earlier issues (part 1 by Ron S. Barrat published in Syst Technol n 21 Jun 1974 p 15-21; part 2 published by R. S. Barrat and J. M. Chambers in Syst Technol n 23 Mar 1976 p 21-28). These articles gave the background to MLS and a description of the ground subsystem. The present article summarizes the two earlier articles and goes on to describe in detail the airborne subsystem and some of the trials results.