I have an Airline Guide from 1977. GFK had 15 flights a day back then. Six to MSP ( 3 North Central DC9, 3 Northwest 727), two flights to Denver on Frontier (1 via Fargo, 1 via Rapid City), one flight Winnipeg on NW, two flights to Omaha via Fargo and Sioux Falls on NC with Convair 580s, plus 580's to Devils Lake and TRF on to MSP. Now with 3 regional jets on Delta and Allegiant, the contrast is stark.