What percentage of the measure of an airline flight's passenger carrying capacity does the IATA's member airlines account for?
International Air Transport Association:  Consisting of 278 airlines, primarily major carriers, representing 117 countries, the IATA's member airlines account for carrying approximately 83% of total Available Seat Kilometers air traffic. Available seat miles: Available seat miles (ASM) or Available seat kilometres (ASK) is a measure of an airline flight's passenger carrying capacity.
83%