How do we know the reason for a flight being late or cancelled?
Since June 2003, the airlines that report on-time data also report the causes of delays and cancellations to the Bureau of Transportation Statistics. Reported causes of delay are available from June 2003 to the most recent month.
Which airlines report on-time data?
Carriers that have 1 percent of total domestic scheduled-service passenger revenue report on-time data and the causes of delay. In 2013, there are 16 carriers reporting these numbers, including one that reports voluntarily.
Do the airlines report the exact cause of the delay?
The airlines report the causes of delay in broad categories that were created by the Air Carrier On-Time Reporting Advisory Committee. The categories are Air Carrier, National Aviation System, Weather, Late-Arriving Aircraft and Security. The causes of cancellation are the same, except there is no late-arriving aircraft category.
These are the year-by-year numbers:
Delay Cause by Year
|Percent of Total Delay Minutes|
|Air Carrier Delay||26.3%||25.8%||28.0%||27.8%||28.5%||27.8%||28.0%||30.4%||30.1%||31.9%||29.4%|
|Aircraft Arriving Late||30.9%||33.6%||34.2%||37.0%||37.7%||36.6%||36.2%||39.4%||40.8%||41.4%||42.1%|
|National Aviation System Delay||36.5%||33.5%||31.4%||29.4%||27.9%||30.2%||30.6%||25.7%||24.8%||22.5%||24.2%|
SOURCE: Bureau of Transportation Statistics
Is it true that weather causes only 4 percent of flight delays?
That category consists of extreme weather which prevents flying. There is another category of weather within the NAS category. This type of weather slows the operations of the system but does not prevent flying. Delays or cancellations coded "NAS" are the type of weather delays that could be reduced with corrective action by the airports or the Federal Aviation Administration. During 2011, 75.5 percent of NAS delays were due to weather. NAS delays were 24.8 percent of total delays in 2011.
How many flights were really delayed by weather?
A true picture of total weather-related delays requires several steps. First, the extreme weather delays must be combined with the NAS weather category. Second, a calculation must be made to determine the weather-related delays included in the "late-arriving aircraft" category. Airlines do not report the causes of the late-arriving aircraft but an allocation can be made using the proportion of weather related-delays and total flights in the other categories. Adding the weather-related delays to the extreme weather and NAS weather categories would result in weather's share of all flight delays.
Weather's Share of Total Delay Minutes
SOURCE: Bureau of Transportation Statistics
The Air Carrier On-Time Reporting Advisory Committee created this reporting system. The committee believed that separating the extreme weather delays from the weather delays that could be fixed through improvements to the system, would provide a truer picture of the extent of weather delays. The separate reports would provide the system’s managers with better information for making improvements.
Is more information available on the Air Carrier On-Time Reporting Advisory Committee?
DOT formed an Air Carrier On-Time Reporting Advisory Committee in August 2000 to consider changes to the current on-time reporting system so that the public would have clear information about the nature and sources of airline delays and cancellations. This task force recommended the creation of a reporting framework for collecting information about the causes of airline delays and cancellations.
In 2001, BTS conducted a pilot program with four airlines to test the monthly reporting of causation. BTS based the final rule on the recommendations of the task force, the results of its pilot project, its outreach efforts to the aviation community and comments received after a proposed rule was published in December 2001.
To view a copy of the rule, go to the Docket Management System website, http://dms.dot.gov/, and follow the instructions for viewing the documents in Docket No. OST 2000-8164.
Is more information available on the causes of delays and cancellations?
Cause of delay numbers can be found on the BTS website at http://www.transtats.bts.gov/OT_Delay/OT_DelayCause1.asp This page allows searches by time period and by airline or airport. It also has calculations for weather’s share of flight delays and a breakdown of NAS delays by category. More data can be found on the TranStats database at http://www.transtats.bts.gov/Fields.asp?Table_ID=236 Also, the Department’s monthly Air Travel Consumer Report includes a summary of causes of delay numbers reported by each carrier for the most recent month. The report can be found at http://www.dot.gov/airconsumer/air-travel-consumer-reports.