Aircrew reports of turbulence at heights between 20,000 and 40,000 ft. are analysed to show geographical and seasonal variation in incidence of turbulence. It is found that there is generally a summer minimum of turbulence and an autumn or winter maximum.

Reports of the occurrence or non-occurrence of turbulence have been made for the flights of Comet 4B aircraft of British European Airways. Although the assessment of the turbulence was no more than subjective it was thought that the uniform nature of the aircraft, operating over a large number of flight sectors in the European and Mediterranean areas, and the fact that ‘nil’ returns were also made, could give useful indications of the geographical and seasonal variation of the incidence of the high-level turbulence. An analysis of the reports, made during a period of twelve months, is presented here.