Weather ruled out as biggest cause of US flight delays

Bloomberg

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 government began collecting such data in 2003.

Airline Factors
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 six out of 100 flights were held up by factors attributed to the airlines. That doesn’t include the ripple of delays that a late flight inflicts on subsequent ones.
And the difference is even more substantial when measured by the aggregate amount of time flights are tardy. Airline-caused delays totaled 20.2 million minutes last year — 2.7 million more than all other categories combined.
Airlines for America, the Washington trade group representing most of the large carriers, said the government numbers don’t tell the whole story. Airlines helped the system achieve an on-time rate of about 80 percent by reducing the number of flights, which eased congestion at the busiest airports, Sharon Pinkerton, the group’s vice president for legislative and regulatory policy, said in an interview.
A delay is defined as any flight that reaches the gate at least 15 minutes later than its scheduled arrival time. Delays attributed to the airlines include such factors as maintenance, pilots who didn’t arrive on time, aircraft cleaning or baggage loading. Or, as some unlucky passengers recently learned, computer glitches. A power loss at Delta’s computer center on Aug. 8 prompted more than 2,000 canceled flights worldwide. A computer failure at Southwest Airlines Co. on July 20 is expected to cost “tens of millions” of dollars after more than 2,300 flights were canceled, the
company said.
Delays in recent years are far less severe than the period from 2006 through 2008, when there were more flights and carriers fought fiercely for market share at overburdened airports such as those around New York and Chicago. Since then, airlines deserve credit for cutting flights and working collaboratively with the FAA, according to the agency and academics who have studied the data.

Sea Change
But the swelling share of airline-caused flight delays marks a sea change from the days starting in 2003 when passenger outrage prompted regulators to require carriers to report the reasons flights were delayed.
Last year the carriers caused 20.2 million minutes of delays, according to their own reports to the government. The category known as “National Aviation System” — mainly weather, congested airports and problems with the air-traffic system — led to 14.3 million minutes of delay.
Other categories are reserved for severe weather events, such as hurricanes or snowstorms that shut down airports, and security delays. Even when combined with the national aviation delays, the total, 17.5 million minutes, is still less than the airline-caused ones. Planes were held up for another 25 million minutes last year for undetermined reasons because the previous flight arrived late, something that reverberates through the system, according to the data.

Flight Time
From a high of almost 600,000 delays in 2007 blamed on the U.S. aviation system, the total fell to 316,684 last year. The total time that flights were late due to this category fell almost in half from 28.2 million in 2007.
One reason: The system has gotten better at adapting to weather that slows flights, which includes thunderstorms, fog, unusual winds and snow. Flights held up by weather caused about half of all minutes of delay in the early 2000s. That fell to less than one-third the past two years, according to the data.
Since 2008, most of the overall decline in tardy arrivals has been due to a reduction in the number of flights after bankruptcies and mergers, the introduction of new air-traffic technology and improvements in how the FAA’s controllers have adapted to thunderstorms in the summer months, according to John Hansman, a Massachusetts Institute of Technology aeronautics professor who has studied the issue.
It’s less clear why the delays attributed to airlines haven’t fallen with other categories, said Hansman and Vikrant Vaze, an assistant engineering professor at Dartmouth College who has also researched the subject. Airlines aren’t required to provide the government with underlying reasons they caused flights to be late.
“‘Air carrier delays’ — that category has been an enigma to me,” Vaze said.