Airlines reported 18 tarmac delays of more than three hours on domestic flights and one tarmac delay of more than four hours on international flights in July, according to the U.S. Department of Transportation’s Air Travel Consumer Report. Sixteen of the long domestic tarmac delays took place on July 13 and involved flights bound for or departing from Chicago O’Hare Airport, where severe storms affected the area that day. All of the reported tarmac delays are under investigation by the department.

The larger U.S. airlines have been required to file complete reports on their long tarmac delays for domestic flights since October 2008. Under a new rule that took effect Aug. 23, 2011, all U.S. and foreign airlines operating at least one aircraft with 30 or more passenger seats must report lengthy tarmac delays at U.S. airports.

Also beginning on Aug. 23, 2011, carriers operating international flights may not allow tarmac delays at U.S. airports to last longer than four hours. There is a separate three-hour limit on tarmac delays involving domestic flights, which went into effect in April 2010. Exceptions to the time limits for both domestic and international flights are allowed only for safety, security, or air traffic control-related reasons. Severe weather could cause or exacerbate such situations.

The reporting carriers posted an on-time arrival rate in July of 76 percent, down from both July 2011’s 77.8 percent mark and from June 2012’s 80.7 percent. Reporting carriers canceled 1.4 percent of their scheduled domestic flights in July, down from the 1.7 percent cancellation rate posted in July 2011, but up from June 2012’s cancellation rate of 1.1 percent.

At the end of July, there were four flights that were chronically delayed -- more than 30 minutes late more than 50 percent of the time -- for three consecutive months. There were 14 additional flights that were chronically delayed for two consecutive months.  There were no chronically delayed flights for four consecutive months or more.

In July, the carriers filing on-time performance data reported that 6.07 percent of their flights were delayed by aviation system delays, compared to 4.82 percent in June; 9.03 percent by late-arriving aircraft, compared to 6.98 percent in June; 6.32 percent by factors within the airline’s control, such as maintenance or crew problems, compared to 5.62 percent in June; 0.82 percent by extreme weather, compared to 0.50 percent in June; and 0.04 percent for security reasons, equal to 0.04 percent in June.

Weather is a factor in both the extreme-weather category and the aviation-system category. This includes delays due to the re-routing of flights by DOT’s Federal Aviation Administration in consultation with the carriers involved.  Weather is also a factor in delays attributed to late-arriving aircraft, although airlines do not report specific causes in that category.

Data collected by BTS also shows the percentage of late flights delayed by weather, including those reported in either the category of extreme weather or included in National Aviation System delays. In July, 40.71 percent of late flights were delayed by weather, up 6.54 percent from July 2011, when 38.21 percent of late flights were delayed by weather, and up 35.79 percent from June when 29.98 percent of late flights were delayed by weather.

U.S. carriers reporting flight delays and mishandled baggage data posted a mishandled baggage rate of 3.52 reports per 1,000 passengers in July, down from July 2011’s rate of 3.72, but higher than June 2012’s rate of 3.35.

In July, carriers reported three incidents involving the loss, death, or injury of pets while traveling by air, down from the six reports filed in July 2011, but up from the two reports filed in June 2012.  July’s incidents involved two pet injuries and one lost pet.

In July, the DOT received 2,466 complaints about airline service from consumers, up 91.8 percent from the 1,286 complaints filed in July 2011, and up 49.2 percent from the 1,653 received in June 2012. The report also contains a tabulation of complaints filed with DOT in July against airlines regarding the treatment of passengers with disabilities. The department received a total of 97 disability-related complaints in July, up from both the total of 75 complaints filed in July 2011 and the 81 complaints received in June 2012.

Highest on-time arrival rates in July were Hawaiian Airlines (89.6 percent), Alaska Airlines (88.6 percent) and US Airways (82.0 percent). The lowest on-time arrival rates were United Airlines (64.1 percent), ExpressJet Airlines (67.7 percent) and American Eagle Airlines (75.4 percent).

Domestic flights with longest tarmac delays exceeding three hours were: Shuttle America flight 3512 from Chicago O’Hare to Atlanta, 7/13/12, delayed on tarmac 257 minutes; ExpressJet Airlines flight 6180 from Rapid City, S.D. to Chicago O’Hare, 7/13/12, delayed on tarmac 249 minutes; ExpressJet Airlines flight 5918 from Richmond, Va. to Chicago O’Hare, 7/13/12, delayed on tarmac 242 minutes; SkyWest Airlines flight 5211 from Cleveland to Chicago O’Hare, 7/13/12, delayed on tarmac 221 minutes; ExpressJet Airlines flight 5875 from Harrisburg, Pa. to Chicago O’Hare, 7/13/12, delayed on tarmac 219 minutes

There was only one international flights with a tarmac delay exceeding four hours: Caribbean Airlines flight 526 from Georgetown, Guyana to New York JFK, 7/7/12, delayed on tarmac 243 minutes.

Airlines with the highest rates of canceled flights were ExpressJet Airlines (3.4 percent), American Eagle Airlines (2.9 percent) and United Airlines (2.3 percent). Airlines with the lowest rates of canceled flights were Virgin America (0.1 percent), Hawaiian Airlines (0.2 percent) and Frontier Airlines (0.2 percent).