Airline miscues -- such as the computer glitches that grounded hundreds of thousands of passengers this summer -- are now the biggest cause of flight delays in the US. Late arrivals triggered by mechanical breakdowns, a lack of flight crews and other factors attributed to the airlines were the largest category of delay last year for just the second time, and by the widest margin, since the govt began collecting such data in 2003. It exceeded what had been traditionally the biggest causes: weather and hiccups in the FAA’s air-traffic system, according to data provided by the airlines to the DoT. The 323,454 flights delayed last year due to the airlines exceeded the number attributed to the FAA by 6,770, the biggest margin ever. Almost 6 out of 100 flights were held up by factors attributed to the airlines. <br/>