Despite mass groundings, Delta has a strong track record

Travelers check the Delta departures board at LaGuardia Airport , August 8, 2016.

Despite a well-publicized breakdown that grounded thousands of flights on Monday and Tuesday, Delta Air Lines actually has a good track record when it comes to delays and cancellations.

According to government data, Delta is the least likely of the four biggest U.S. airlines to leave customers stranded or inconvenienced by late flights. Delta flights have been on time for 85 percent of flights over the last five years — at least 6 percentage points better than American Airlines, United or Southwest.

In the first five months of the year, Delta managed to operate more than 50,000 flights each month while on average canceling fewer than 300 and delaying less than 7,000 monthly. Over the last two days, however, the company has been forced to cancel at least 1,300 flights.

The mass delays and cancellations were caused by a power outage at the company's Atlanta headquarters and a breakdown of critical network equipment that failed to switch to a backup system. The event is going to put a nasty dent in the company's otherwise impressive statistics.

A company spokesperson declined to comment on how important the statistics it reports to the U.S. Department of Transportation are to the company, but did say that Delta "prides itself on serving its customers," and that its team is "focused on delivering the best experience and operational performance for our customers."

About a third of Delta's delays over the last five years were caused by factors that are within the control of the airline — what the Federal Aviation Administration calls "carrier delays." The rest were caused by late arrivals, air traffic control issues, severe weather or security delays.

Delta is certainly not alone in experiencing significant mass delays and cancellations in recent years. Flight delays tend to rise during periods of economic growth, when higher traffic puts stress on aging control systems. More of those delays are caused by carrier failures today than a decade ago, while fewer are caused by weather.

Just last month, Southwest Airlines experienced a computer system failure that delayed or canceled more than 2,000 of flights over several days. About 800 Southwest flights were delayed in October due to a system outage. United Continental and American Airlines have also suffered from outages in recent years.

The largest U.S. airlines — which account for about 85 percent of domestic air traffic — are required to report on-time performance for each flight to the government each month, and to disclose that information on their websites and to travel agencies. That wide availability is meant to influence consumers and encourage good service from the carriers.

The Department of Transportation can fine airlines for unfair practices and requires airlines to offer refunds when a flight is canceled or significantly delayed, said a department spokesperson. Delta has already offered compensation for passengers who were affected by the latest disruptions.

"Consistently poor on-time performance would likely cost airlines customers, so airlines value on-time performance as a competitive matter," the spokesperson said. "In addition, delayed and canceled flights cause costly downstream operational disruptions — additional delays or cancellations because a planned aircraft or crew is not in place or because pilots have 'timed out.'"

Delta's systems were back online on Tuesday, but were still in "recovery mode," according to the company. About 300 flights were canceled on Tuesday morning.

"We are sorry for what many of our customers have experienced over the past 24 hours, including those who remain at airports and continue waiting for their flights," Dave Holtz, Delta senior vice president, said in a statement Tuesday morning. "We are doing everything we can to return our operation to normal reliability, but we do expect additional delays and cancellations."