Transmission Availability Data System (TADS)
On October 23, 2007, the NERC Board of Trustees (Board) approved the collection of the Phase I TADS data, beginning in calendar year 2008. On October 29, 2008, the Board approved the collection of Phase II TADS Non-Automatic Outage Data, beginning in 2010. TAD collects transmission outage data in a common format for: 
  1. Bulk Electric System AC Circuits (Overhead and Underground)
  2. Transmission Transformers (No Generator Step-up Units) 
  3. Bulk Electric System AC/DC Back-to-Back Converters 
  4. Bulk Electric System DC Circuits

TADS efforts began in 2006 with the formation of the TADS Task Force under the NERC Planning Committee. This task force designed TADS and the associated processes for collecting TADS data. On June 30, 2009, the task force issued its first reports for data collected in 2008. On July 1, 2009, the task force was retired and replaced with the TADS Working Group. This change recognized the ongoing design and oversight of TADS that is more appropriately assigned to a working group than a task force. NERC uses the information to develop transmission metrics that analyze outage frequency, duration, causes, and many other factors related to transmission outages.

In 2020, the TADS Working Group became the TADS User Group (TADSUG).  The TADSUG performs the same functions as the TADSWG.  However, it no longer reports into the NERC Committee structure. Instead, it reports to the NERC Performance Analysis Department.

While TADS is not intended to provide determinative performance measures, it is used to quantify certain performance aspects. In addition to collecting simple transmission equipment availability, TADS will collect detailed information about individual outage events that, when analyzed at the regional and NERC level, will provide data that may be used to improve reliability.

All TADS-related material is available for download from the TADS User Group.

For more information, please contact


 TADS News

​Effective August 26, 2020 the TADS Reporting Workbook has been updated. The TADS Reporting Workbook no longer contains the following items:

  • Defunct Regions FRCC and SPP
  • Multi Owner Common Structure Flag
  • Planned Outages


 Data Submission

Deadlines for Data Submission into WebTADS are:

Reporting Deadline*Period of Operation to Report
February 15​Any updates for the prior year
May 15​Quarter 1: January 1 - March 31
​August 15​Quarter 2: April 1 - June 30
​November 15​Quarter 3: July 1 - September 30
​February 15​Quarter 4: October 1 - December 31

*When a deadline falls on a weekend or holiday, reporting will be extended through the following business day.

expand Grouping : webTADS Application Updates ‎(7)
expand Grouping : Key TADS Documents ‎(2)