But a closer look at the BTS data shows that the three main causes for delay are backups within the US aviation system, weather, and airline related issues.
(A flight is considered delayed if it's more than 15 minutes later than scheduled. )
According to the BTS, about 50% of all tardy flights between June of 2015 and June 2016 are attributed to circumstances within the airline's control such as aircraft maintenance, crew scheduling, refueling etc. This includes the nearly 210,000 flights there were delayed during this period due to late arriving inbound flights caused by airline-related issues.
At the same time, 30% of the delays can be blamed directly on weather. According to the BTS, this includes roughly half of the flights delayed due to the US aviation system, as well as 33% of delays due to late arriving inbound aircraft.
Finally, about 15% of the delays are caused by broad issues within the US aviation network. According to the BTS, this means problems with air traffic control, airport operations, and heavy traffic volume.
As bad as delayed flights may be, they don't happen as often as one would expect once you consider America's aging aviation infrastructure coupled with surging demand for air travel and unpredictable weather. Even with these issues, 81.5% of flights did arrive on time. That's up from the 79.7% on-time arrival rate in 2003-2004, when the BTS first began publishing this data.