Concepts of Traffic Flow Management

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Scope of Traffic Management Initiatives (TMIs)

Scope, as it relates to Traffic Management, can be defined as the range of influence or impact for a particular TMI.  Flights falling outside the scope of a program will not be affected by that particular program.  Scope is determined by one of two ways - distance or tiers.


Sometimes the scope for TMIs will be determined by distance from a particular airport.  This will be noted under a program's scope as something like "Distance - 1200 miles+CZY", meaning that all flights originating from within 1200 miles or Toronto Center (CZY) would be included in the program.

Defining scope by distance can be helpful in some situations, giving managers more precise control over what flights will be included in or excluded from a program.


More commonly, program scope will be defined by tiers.  The word “tier” describes a geographical area that is based on Air Route Traffic Control Center (ARTCC) boundaries. It may be used for implementing TMIs.

Tiers are best explained using a graphic.  In the image below, the ARTCC selected is New York Center (ZNY) - shown in green.  The yellow ARTCCs would be considered "First Tier" since they are immediately adjacent to ZNY.  The blue ARTCCs are "Second Tier" because they are, in turn, adjacent to the First Tier ARTCCs. This is also sometimes indicated as ZNY2. 

Also note that tier information is generally inclusive, meaning that a Second Tier program would also include First Tier centers.

Here is a practical example of how scope would be interpreted:

A Second Tier ground delay program for Teterboro, NJ (TEB) has just been implemented.  Would a flight leaving from Colorado Springs, CO (COS) be included in the program and issued an EDCT?  How about a flight from Minneapolis, MN (MSP)?

  • The COS flight - COS is located in Denver Center (ZDV) which does not border either ZNY (where TEB is located) or any of the ZNY First Tier centers.  Therefore, the flight would be exempt from the GDP and would not be issued an EDCT.
  • The MSP flight - MSP is located in Minneapolis Center (ZMP) which is a Second Tier center from ZNY.  Therefore, the flight would be caught in the GDP and the flight would likely be issued an EDCT.

There are some variations to the tier description to account for the size and domestic-international services provided by each ARTCC. Here are some additional scope definitions that are used:

  • Six West - ZAB / ZDV / ZLA / ZLC / ZOA / ZSE
  • Ten West - ZAB / ZDV / ZFW / ZHU / ZKC / ZLA / ZLC / ZMP / ZOA / ZSE
  • Twelve West - ZAB / ZAU / ZDV / ZFW / ZHU / ZKC / ZLA / ZLC / ZME / ZMP / ZOA / ZSE
  • No West - exclude ZAB / ZDV / ZLA / ZLC / ZOA / ZSE
  • Ten East - ZBW, ZNY, ZDC, ZJX, ZMA, ZTL, ZME, ZID, ZAU

More information about tier descriptions can be found on the FAA's web site at: