What Are the Most Common Reasons For Flight Delays in the U.S.?

It may not seem like it sometimes, but airline schedules are far more likely to be on time than not—according to data from the U.S. Bureau of Transportation Statistics (BTS), 81.19% of all flights in 2021 were on time.

That number is actually down from 2020, a year when 84.63% of all flights were on time, but up from 2019, a year when 79.21% of all flights were on time, and 2018, a year when 79.38% of all flights on time.

In general, your odds of having your travel plans impacted by issues at the airport have hovered around 20% for the past few years, but there’s still a lot that can run through your mind when checking your flight status the night before you’re set to travel or on your way to the airport.

Here’s what is most likely to delay or impact your travel according to the latest data from the BTS:

1. Air Carrier Delay (6.57%)
This category includes all delays that came “due to circumstances within the airline’s control,” BTS said.

That means if there are maintenance issues, if a crew is waiting for flight attendants or pilots to show up, or if there is a delay cleaning the aircraft, loading baggage, or fueling, then those delays would fall into this category.

For 2021, Air Carrier Delays affected 6.57% of all flights within the U.S., a percentage higher than any other reason.  That number is almost double the rate of Air Carrier Delay issues in 2020 (3.35%) and a little higher than the rate for 2019 (5.23%).

2. Aircraft Arriving Late (5.34%)
More than once in 2021, a single event causing delays caused a snowball effect of flight delays and cancellations at a U.S. airport. This included a wind threat in Dallas in October than caused over 2,300 flights to be canceled by American Airlines and another 2,000 canceled by Southwest just a few weeks later because of weather issues.

The BTS defines this category as “a previous flight with the same aircraft arrived late, causing the present flight to depart late.”

Weather issues, or other delay issues, causing aircraft to arrive late was the reason behind the delays for 5.34% of all total flights in 2021. That is almost double the rate of 2020, which had just 2.34% of all flights impacted by aircraft arriving late.

3. National Aviation System Delay (4.12%)
This category is maybe the broadest of the data that the BTS tracks. According to the Bureau, this includes delays and cancellations attributable to the national aviation system…such as non-extreme weather conditions, airport operations, heavy traffic volume, and air traffic control.”

In 2021, most of this category of delay was due to non-extreme weather (46.76%), followed by volume (39.44%), closed runway (8.82%), and the “other” (4.79%).

4. Canceled (1.72%)
While it may not seem like it, flights being canceled are a rare occurrence according to the data tracked by BTS.

In 2020, 5.99% of all flights were canceled, but that number, with the COVID-19 pandemic, is clearly an outlier. In 2019, 1.82% of flights were canceled. And, in 2018, 1.62% of all flights were canceled.

5. “Extreme” Weather (.74%)
“Extreme” weather is responsible for less than 1% of all flight delays in the U.S. despite its reputation for being the biggest culprit on the list. But that might just come down to how BTS categorizes it.

According to BTS, when combined with the other weather categorization in the National Aviation System Delay category, and how weather impacts aircraft arriving late, weather is sometimes responsible for up to 34% of all flight delays depending on what month you’re looking at.

In 2021, for instance, February had 33.85% of all flights delayed by weather and in November that number dropped to 11.05%.

Non-weather delays still far outnumbered the percentage of weather delays regardless of what month you are examining.