Introduction In response to Recommendation 606 (MOB-87)@ Question 94/8 asks what is the bandwith required for radio altimeters to maintain the necessary operational accuracy. The International Civil Aviation Organization (ICAO) has conducted a survey among its Member States and major manufacturers of radio altimeters. In addition@ a study covering both current and projected future types of radio altimeters has been carried out by the UK Civil Aviation Authority [Ingless@ 1989].