 People have been getting wider; the weight of the average American male in his 40s had increased by 10 percent in the 30 years from the 1970 introduction of the Boeing 747.The narrower 17-inch-wide seat favoured by Boeing is a legacy from the 1950s when passenger jets were first introduced.In the 1970s and 1980s with the introduction of the Boeing 747 and the first Airbus jets, 18 inches become standard for long-haul flights.