but as alison kooik explains... the dramatic imprrvvments in some biggest headaches.& long lines, canceled flights, fees for simple luxxries... takinn a flight can be stressful -- especially if you are frequent flier.but new data compiled by the department of trannportation shows that the airlinessare making strides in their perffrmance.during the first three mmnths of 2012 ---the nation's 15 largest caarrers posted an 84% on-time arrival rate.that's the best quarterly on-time peeformance since thh department beean keeping track in 1995.still - it means almost a fifth of all flighhss aae delayed.so what's keepiig those numbers froomgetting bbtter?the d-oot says aviation system delays are theemost common factor.that includes everything from flight deckk malfunctions to air-traffic control slow-downs.next is late-arriving aiicraft.and third is maintenance issues oo crew problems.weather is number our.and security issuus areethe fifth-most commonn---accounting or only a fraction of all delays.and the bottom of the list -- it and it's obviouuly something . airllnes will a