ETMSC
Contents |
Overview
ETMSC source data are created when pilots file flight plans and/or when flights are detected by the National Airspace System (NAS), usually via RADAR. Enhanced Traffic Management System Counts (ETMSC) records are assembled by the FAA Air Traffic Airspace (ATA) Lab by combining electronic messages transmitted to the En Route Modernization Automation Modernization (ERAM) system for each flight into a complete record of that flight. ETMSC has three views: Airport, City Pair, and Distributed OPSNET. The three views provide different perspectives on the ETMSC data.
ETMSC contains every flight record constructed. It includes information about Commercial Traffic (air carriers and air taxis), General Aviation, and Military to and from every landing facility as well as fixes, both in the US and in nearby countries that participate in the ETMS system.
Data for each month are made available to the ETMSC data access system approximately 10 days after the end of the month. Preliminary next-day ETMS data and enhanced five-day data are used to construct ASPM records, but these preliminary data are not reported in the ETMSC data access system.
Data Sources and Update Cycle
The flight counts reported in ETMSC are derived from flight records assembled by the FAA Air Traffic Airspace (ATA) Lab by threading the many ETMS messages together. These flight records may be incomplete records when one end is missing, or when only planned components are available. For example, flights may be missing DZ or AZ time (or both), or may have incorrect or missing airport codes and equipment codes. Missing AZ or DZ may cause the flight to be assigned to the 25 hour.
ETMSC data is available by day from January 2000 and is updated monthly.
Data Availability
Data for each month are made available to the ETMSC data access system approximately 10 days after the end of the month. Preliminary next-day ETMS data and enhanced five-day data are used to construct ASPM records, but these preliminary data are not reported in the ETMSC data access system.
Data Limitations
While ETMS reliably captures the vast majority of traffic, it has several limitations and challenges. First, due to limited radar coverage and incomplete messaging, ETMS may exclude certain flights that do not enter the en route airspace and other low-altitude flights. In addition, of the 35,000 location identifiers reported over time, only the top few thousand, accounting for over 95% of traffic, are reliable. The others are waypoints or other references to locations not associated with an airport.
Change History
ETMSC data are typically not modified or updated after the monthly files are received, except in the rare case of the discovery of a significant problem with the data files.
System Documentation
In ETMSC, data are arranged by the following:
- flight type (domestic, foreign, US to foreign, foreign to US)
- source-provided user class (commercial, air taxi, freight, general aviation, military, other)
- value-added equipment type (piston, turbine, jet, helicopter, other)
- value-added equipment Weight Class (heavy, 757, large jets, medium, small, other)
- business jets
- regional jets
ETMSC records are available from January 2000 to present less one month. Records are updated at the end of the month for the prior month's data.
Value-Added and Computed Values
Some fields in ETMSC are derived fields created for policy research and other purposes.
Value-Added Fields
Equipment observed in the ETMS records is identified as Business Jet or Regional Jet using the APO system look-up tables. Number of seats, Weight Class, and Type of flight are determined from the foreign, domestic, or oceanic flags. Seats are in look-up tables. ETMS reported equipment type by carrier identifies the number of seats. If there is no equipment type by carrier, this is assigned a default number of seats and equipment set to "O" for Other.
Computed Fields
The Distance Flown is the Great Circle Route calculated using the latitude and longitude of each end as found in the ETMS_Locids table. Time Flown is calculated as the difference between Wheels Off (DZ) and Wheels On (AZ), if both are present. Some flight records having invalid airport codes are left with incorrect latitude and longitude, which results in incorrect distance flown.
ETMSC OPSNET Proration
ETMSCounts (ETMSC) process the individual flight records provided by the ATA Lab and assemble them from ETMS. The ETMSC process, among other things, creates a summary of traffic by day and hour based on the DZ (departure) and AZ (arrival) message times. ETMSC summarizes traffic by user classes reported by ETMS (C-Commercial, F-Freight, T-Air Taxi, M-Military, G-General Aviation, O-Other for unknown).
OPSNET Operation Counts
OPSNET Operations are reported as a single number in several categories per day. It does not report separate departure and arrivals, nor does it report these counts by hour of the day. ETMSC distributes the OPSNET reported categories of operations into departures and arrivals and by hour of the day using the distribution of flights determined by ETMS.
Computation Details
ETMSC groups flights into three user groups: Commercial, General Aviation, and Military. These three groups were chosen because of the slightly different user classes used by ETMS and OPSNET. The following table shows how ETMSC groups the user classes reported by ETMS and OPSNET into these three groups:
| ETMSC User Group | ETMS User Class | OPSNET User Class |
|---|---|---|
| Commercial | C – commercial,
F – Freight, T – Air Taxi, |
Air Carrier,
Air Taxi |
| General Aviation | G – General Aviation | General Aviation,
Local General Aviation |
| Military | M – Military | Military,
Local Military |
Distribution
Once the user classes are grouped by the ETMSC user groups for the day, the ETMS daily distribution by departure and arrival by hour is used to distribute the OPSNET counts. This is done with percentages to the nearest whole number. Then the day is checked to be equal to the OPSNET total for the day and is balanced by adding or removing single counts as needed. This method does not require ETMS and OPSNET counts to be equal. Also, ETMS counts will not match ETMSC or ASPM counts because some of the ETMS records used for this distribution are not used or do not have an AZ, DZ, or Equipment code. This does ensure OPSNET data is distributed over just 24 hours, whereas ETMSC City Pair Report may have an unknown time allocated to a 25 hour.
User Manual
View the ETMSC Manual for detailed information on how to create reports.
Definitions of Variables
For more information about these topics, please see the Definitions of Variables for the ETMSC system.
