British Telecom International (BTI) has introduced an aeronautical telephone service known as the Skyphone. This service uses 9.6 kbit/s speech codecs because of the limited satellite power available. Because of the need to achieve operation of aeronautical telephones between any aircraft and any ground station in any country, the technical specifications have been agreed internationally. After extensive testing of the various speech codecs proposed for the service by companies from several different countries, the codec designed at British Telecom Research Laboratories (BTRL) was found to be the best and is to be used both for international telephony and for air traffic control. This paper gives a brief description of the Skyphone and the factors which influence the speech codec design and then describes the codec designed by BTRL for the service.