 Earlier that year the CAB had instituted what became known as the "3 and 8 rule" which limited nonscheduled airlines' monthly flights to eight between any two U.S. cities and three on specified high-density routes.No non-sked could feasibly sustain itself on such a slim diet, and the measure was viewed as a death sentence by leaders of the irregular air industry.Nonetheless, a select group of non-skeds not only persevered but prospered in the ensuing years, though many were far from scrupulous in their observance of the CAB's economic constraints.