Air Vice-Marshal Professor John Ernsting was recognised worldwide as a leading authority in aviation medicine; his pioneering work led to the development of special life-support equipment allowing military aircrew and civil aircraft to operate at extreme altitudes. Ernsting was commissioned into the RAF Medical Branch in 1954. For 25 years he worked in the altitude division of the Institute of Aviation Medicine (IAM) at Farnborough, and he specialised in studying the physiological aspects of flying at high altitudes, including protection against hypoxia and decompression sickness, leading teams carrying out the research and development of specialised pressure suits, helmets and breathing assemblies needed for new higher flying aircraft. The work he co-ordinated at the IAM on cabin pressurisation also led to an acceptance that the cabin pressure in Concorde should be 6,000ft, rather than the internationally-agreed 8,000ft for airliners operating at lower altitudes. His finding also influenced the design of emergency oxygen supplies in airliners, and also influenced the size of the cabin windows in Concorde. In 1971 he was appointed its head, with responsibility for research, teaching and the direction of the specialist staff. During the late 1960s he was the RAF's aeromedical project officer for the development of the British versions of the American-built F-111, Phantom and Hercules aircraft. He also conducted research into a system of generating an oxygen supply in a combat aircraft. During a sabbatical year at the USAF School of Aerospace Medicine, he worked on a development of the idea, which was eventually installed in the later marks of the Harrier aircraft. He returned to the IAM in 1980 as deputy director of research. He was chairman of the aeromedical and life-support system working parties for the Tornado and for the formative phase of the Eurofighter project. In 1988 he was appointed commandant of the IAM, a post he held until his retirement in December 1992. He remained a civil consultant for the next two years. He also placed great emphasis on correct and realistic training, and played a key role in the creation and development of the RAF's Aviation Medicine Training Centre. On leaving the RAF he moved to King's College, London, to teach and conduct research in human and aviation physiology. He was the honorary civil consultant in aviation medicine to the RAF, aeromedical adviser to BAE Systems and a past president of the International Academy of Aviation and Space Medicine. Ernsting was a member of numerous specialist and international working parties, and chaired a number of Nato committees and workshops. He wrote many professional papers and was the co-editor of Aviation Medicine, the standard reference for all civil and military aviation medicine practitioners. He was elected a Fellow of the Royal College of Physicians, of the Aerospace Medical Association and of the Royal Aeronautical Society and was awarded many national and international prizes. He was appointed OBE in 1959 and CB in 1992.