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Aviation Revenue Freight Ton-Miles
Aviation Revenue Freight Ton-Miles
Source: U.S. Department of Transportation, Bureau of Transportation Statistics, Office of Airline Information (government).
TSI uses aviation revenue freight ton-miles data reported by air carriers to the Bureau of Transportation Statistics' Office of Airline Information (OAI). The data, referred to as the T-1 dataset under the T-100 and T-100f databases, are published monthly in Air Carrier Traffic Statistics (the Green Book) produced by OAI. Reference to the Green Book can be found at http://www.bts.gov/oai/sources/.
The T-100 databases include data reported by U.S. carriers operating between airports located within the boundaries of the United States and its territories. These data fields contain information on passengers, freight, and/or mail enplaned at the origin airport and deplaned at the destination airport.
Data in the Green Book consist of U.S. passenger and cargo capacities and traffic actually carried by carrier and class of service in both scheduled and nonscheduled (or charter) service for the most recent month and 12-month period, and similar data for like periods in the previous year. Data are summarized by U.S. carrier entity and carrier group (major, national, etc.).
Large U.S. certificated air carriers, small certificated air carriers, commuter air carriers, and all-cargo air carriers are required to complete Form 41 Financial and Traffic Reporting Requirements. This form is completed both electronically (mainly by the large carriers) and on paper (small and commuter carriers).
The T-1 dataset includes information on all U.S. commercial air carriers, except air taxis. The dataset does not include foreign air carriers, entities that provide commercial services illegally, in-house air transportation (e.g., corporate jets), general aviation, and air taxis.
Data Quality Questions
A draft data quality assessment, Data Quality Assessment of the Large U.S. Certificated Air Carriers Traffic and Capacity (Form 41, Schedule T-100) Databases, was issued on March 31, 2003, by the Bureau of Transportation Statistics, Office of Statistical Quality. The information below on the T-1 dataset, a product of OAI used in the TSI, was extracted from this data quality assessment.
- Is the data source a frame or a sample?
The data source is a sample. The T-1 dataset in theory provides information on all U.S. commercial air carriers, except air taxis.
- Does the sample cover the entire frame? Or is there some group that is missing or underrepresented in the same sample?
The actual data coverage falls short of the theoretical coverage due to carriers failing to report, late reporting, and errors. Reasons for nonreporting include: new carriers that take time to learn the reporting requirements, noncompliance, and lost records. Analysis of carrier-level data shows some gaps that appear to be missing data. However, gaps are rare for the largest carriers, which account for most of the air transportation services provided. A more common occurrence is for carriers to report data after the normal reporting period. Similarly, errors may occur in the data even though OAI conducts audits of the carrier submissions. For example, a carrier may misreport the number of passengers on a particular route. Errors identified in the audit process are sent back to the carriers for revision and resubmission. The BTS Data Quality Assessment, described above, gives additional detail on these issues.
As noted, data are sometimes reported late. However, the carriers also sometimes revise data after publication in the Green Book.
- Are the data available monthly?
Yes, with occasional disruptions to the schedule due to reporting delays or problems in production. For example, the processing system was recently transferred from a mainframe to a LAN-based system with a simultaneous change in carrier reporting. This resulted in some delays in production. The data are also often revised, as mentioned above, and these historical revisions are released simultaneously with new monthly reports.
- How soon are the data available after the month reported on is over?
The T-1 data generally are available about 10 weeks after the end of the data month.
- Are the data easy to access and use?
The data are easy to access but require some processing to obtain aggregates. However, the disaggregated data for individual carriers are also available.
- Are the microdata available for use?
Two adjustments are made to the most recent T-1 data to improve timeliness. The first adjustment is made to account for carriers that have not yet reported. The adjustments assume that the missing carriers grow at the same rate as carriers that have not yet reported. The second adjustment is to forecast the most recent month based on the 4-quarter growth rate using the most recently available three months. The accuracy of these adjustments is detailed in the next section.
U.S. DOT Office of the Secretary of Transportation for Policy (OST-X) analysis of the data submitted by small certificated Alaskan air carriers identified significant reporting problems when these carriers first began reporting in 2002. OAI has since taken steps to improve the accuracy of the data submissions and OST-X no longer considers this an active area of concern.
Airline traffic and financial data are regulatory data, certified as being correct, by the submitting carriers. The data cannot be changed without the carrier's consent. Although BTS can reject data submissions that are clearly inconsistent, BTS does not have the legal authority to make changes in carrier submitted data.
OAI follows up with carriers regarding questionable data, but the sheer volume of records failing the established edit checks precludes investigation of every issue. Only a small fraction of the records are sent out for review.
- Are there duplicate records?
- Are there outliers in the data?
- Are data missing for individual records? If so, how are they identified?
The biggest source of inaccuracy is due to carriers that fail to report. The problem is mitigated, however, by the consistent reporting by the largest carriers that have provided over 80% of air transportation services in recent years. Overall the data are of high quality and are generally considered the best available.
- How accurate are the key data fields?
The problem of inaccurate reporting exists, but is infrequent.
- Are variances available for this data source? If so, what method was used to calculate variances?
BTS measures the accuracy of the adjustments for missing carriers by comparing the initial estimated growth rates based on the adjustment (the alternative value) to final growth rates based on data at least 4 months after the initial release. If the alternative data is an unbiased predictor of the growth rates from the final data (at least 4 months from initial release) then the average of the paired differences between the alternative and final growth rates should be zero. The t-statistic for the mean difference is -0.56 and is within the (-2.12, 2.12) range for a 5% test at 16 degrees of freedom so we do not reject the null that the mean is zero.
Comparison of Air Freight RTM Growth Rates
Alternative vs. Final Values
|Final||Alternative for Initial Release||Difference||Actual at Initial Release||Difference|
|Average Absolute Error||1.12||24.44|
|Maximum Absolute Error||3.85||21.81|
We measure the accuracy of the forecasts in a manner similar to that used for the alternative data. The t-statistic again indicates the forecasts are an unbiased predictor of future growth rates . However, the forecast error is large enough to be of concern and improving these forecasts remains an active research.
Forecasts of Aviation RTMFM as of February 2006
|Forecast Month||Release Month||Actual||Forecast||Error|
Sumary Statistics for the Forecasts
|Start with June 2004 Release|
|Average Absolute Error||3.5|
|Maximum Absolute Error||13.9|
|Average Absolute Deviation||5.4||5.0||3.5|
|Start with Feb-04 Release|
|Average Absolute Error||4.1|
|Maximum Absolute Error||15.3|
|Average Absolute Deviation||6.4||6.4||4.0|
The forecast values for the 4/20/2004 and 5/17/2004 releases actually forecast 2 months ahead.
Only final data (forecasts for 9/2005 and earlier) are used in the statistics.
Forecasts use only information that was available at the release date.
The forecast uses the most recently available 4-quarter growth rate.
- Are the data comparable over time within the data source? If not, can data be made to be comparable, i.e., combining two data series?
The major inconsistency in the data is the expansion to include small certificated and commuter carriers that previously reported data under 14 CFR Part 298c data. These data are available on a quarterly basis over the entire period, but only covers scheduled operations.
Other Questions and Important Information
- Is sufficient documentation available for the data source?
- Data dictionary:
Documentation is available in the form of data dictionaries and processing steps but is not available for the audit process conducted by OAI.
- Detailed description of the methodology:
Not available to BTS.
- Estimation methods:
Not available to BTS.
- Are other sources available for the same data?
The possibility of supplementing the T1 data with data from the Air Transport Association (ATA) and the Official Airline Guide (OAG) is being examined. These sources provide information on revenue ton-miles (ATA) and schedule information (OAG) that is available sooner than the T1 data.
- Who is the contact for the data source?
Bureau of Transportation Statistics, 1-800-853-1351, firstname.lastname@example.org