airport to knoxville, tennessee, was the worst-performing route last year, not surprising to traveler larsen jay. >> we take this flight a lot. we're always delayed and we're always behind. it's a crapshoot. >> reporter: the flight is a recipe for headaches. the route flies from an airline hub prone to delays. last year 15 of 20 of the least on-time routes came to or from o'hare. it typically uses smaller regional jets, the case for 17 of the 20 worst-performing routes. those regional planes often make several stops a day. josh marks of mass flight says there's a reason for all the delays on short-haul regional routs. >> that's because those regional aircraft are smaller planes. there are fewer number of people that the airlines have to reaccommodate. >> reporter: inside united airline's network operation center in chicago, everyone from maintenance to meteorology is working to keep 5,000 daily flights operating as on-time as possible. >> our key hubs are great. >> reporter: jim deyoung says. the airline tries to anticipatear travel problems but acknowledges some planes get an advantage. do certain types of flights get s a preference if push comes to shove?bl