Last week, a story about a nightmare flight on Delta Air Lines from the Dominican Republic to John F. Kennedy Airport in New York circulated for a day on social media.

The normally four-hour flight turned into a 30-hour ordeal that involved bad weather, turbulence, two flight diversions, an unexpected overnight stay in Manchester, N.H., airsickness bags and inevitable complaints/tweets about customer service.

Unfortunately, air travelers have more to complain about — most of them not as dire as that, but still. Last week, the U.S. Department of Transportation released its Air Travel Consumer Report for 2015. The results weren't encouraging.

The number of airline consumer complaints increased 29.8 percent to 20,170 last year. During the busy holiday season in December, DOT received 1,565 complaints, up 46.9 percent compared with December 2014. Lots of people grumble about flying, but you have to wonder how many people actually follow through by filing a complaint with the DOT.

Typical complaints involve problems with flights, lost baggage, reservations and ticketing, refunds, consumer service, amenities for the disabled and allegations of discrimination. On-time arrivals, a common grievance, were 79.9 percent, up from 76.2 percent in 2014. The most common reasons for flight delays include issues with aviation systems, late-arriving aircraft, maintenance or crew problems, and extreme weather.

Hawaiian Airlines led on-time arrivals in December at 93 percent, followed by Alaska Airlines (85.3 percent) and then Delta Air Lines (83.6 percent). The lowest on-time arrival rates for the month went to Spirit Airlines (68.7 percent), JetBlue Airways (70.1 percent) and Virgin America (71.1 percent). JetBlue and Virgin don't fly to MSP — but, then again, neither does Hawaiian Airlines.

Another area of concern: The number of complaints related to the treatment of disabled passengers increased 19.8 percent last year to 939. And, the number of incidents involving animals increased from 45 in 2014 to 63 last year.

You can read redacted reports of animal deaths and injuries online, although I wouldn't recommend it. Many pets chew their way out of their crates. One gruesome episode involved a Belgian Malinois dog pulling open the door of its crate on a flight from Honolulu to Atlanta (through Los Angeles), and then fatally attacking a nearby cat. Another cat could not be located after it was loaded onto a plane in Detroit. There were several reports of dogs that were injured after chewing their food dishes.

There were a few bright spots in the report. Reporting carriers canceled just 1.5 percent of their scheduled domestic flights during the year, an improvement over the 2.2 percent rate in 2014.

The highest rate of canceled flights went to: Envoy Air (3.8 percent), ExpressJet Airlines (3.4 percent) and SkyWest Airlines (2.9 percent). The lowest rate of cancellations went to Hawaiian Airlines (0.1 percent), followed by Delta and JetBlue (each at 0.3 percent).

The number of complaints alleging discrimination due to race, religion, national origin or sex declined 4.4 percent to 65.

The DOT also reports that carriers posted a bumping rate of 0.76 per 10,000 passengers last year, an improvement over the 0.92 rate reported in 2014.

Janet Moore • 612-673-7752 Twitter: @MooreStrib