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Routes are used to ensure that flights stay with the “flow” of traffic, remain clear of special use airspace, avoid congested airspace, and areas of known weather where aircraft are deviating or refusing to fly.
Route information is contained in the:
- Airport Facility Directory
- Preferential route information in the host computer
- Route Management Tool (RMT)
- North American route advisory circular
- Operational Information System (OIS)
- Federal Air Regulations (FAR)
- Notices to Airmen (NOTAM)
Route information is published in various sources for different purposes, different users and different time frames. The most current information is located on the OIS web page, in the advisories, and in the NOTAMs. These sources document changes to standard routes for the current date or for a special event.
It is common to be issued a route that differs significantly from the filed route. Many times, this is due to the flow of traffic being moved to accommodate severe weather or volume issues.
Normally, air traffic controllers will clear a flight via the route specified by traffic management. The flight may be rerouted in the air or on the ground. The operator should file or amend flight plans with the appropriate routes when the aircraft is 45 minutes or more from the proposed departure time. If within 45 minutes from departure or airborne, ATC facilities will enter the reroutes.
In accordance with Federal Air Regulations (FAR), all operators have the right of refusal of a specific route and may elect an alternative. Alternatives include but are not limited to ground delay, diversion to another airport or a request to stay on filed route.
If a route cannot be accepted due to safety of flight or fuel concerns, the pilot is required to notify the controller that the route cannot be accepted for safety reasons. The controller will work with the pilot to find an acceptable route. If it is known beforehand that the route cannot be accepted, the pilot should notify the clearance delivery controller. However, there may be no alternatives and the flight could be required to accept a delay on the ground until the route becomes available.
Coded Departure Routes are a combination of coded air traffic routings and refined coordination procedures. They are designed to mitigate the potential adverse impacts to ATC and users during periods of severe weather or other events that impact the NAS. CDRs facilitate electronic coordination of route data.
CDR routes are located in the Route Management Tool (RMT) on the OIS web page. The ATCSCC will issue an advisory when CDRs are in effect.
Only customers that have a signed letter of agreement with the FAA are eligible to use the CDRs between the city pairs in the coded format. However any customer can file a route that corresponds to a CDR. Any pilot may file the route listed in the CDR route string if the field labeled “user file” contains a “Y”. At the present time the FAA is considering making CDRs available to all users. Learn more.
A preferred route is a route that is requested, and that has been published by ATC to inform users of the “normal” traffic flows between airports. They were developed to increase system efficiency and capacity by having balanced traffic flows among high-density airports, as well as deconflicting traffic flows where possible.
Preferred routes are listed in the Airport-Facility Directory and in the Route Management Tool (RMT) on the OIS web page.
Occasionally, a pilot may file a preferred route and immediately be issued a new route upon departure. The reason for this is that there may be other constraints on the system, such as severe weather, that is disrupting normal traffic flows. If a pilot believes that the preferred route is erroneous because the route is never received, he should contact the departure center. Learn more.
The North American Route Program (NRP) specifies provisions for flight planning at flight level 290 (FL290) and above, within the conterminous U.S. and Canada. It enables flexible route planning for aircraft operating at FL290 and above, from a point 200 nautical miles (NM) from their point of departure to a point 200 NM from their destination. Additional flexibility is available by utilizing specified Departure Procedures (DP) and Standard Terminal Arrival Routes (STAR) that have been identified within 200 NM of the airport(s).
Occasionally, a pilot may be taken off an NRP route. This is because there may be times when air traffic requires flights to be on specified routes due to volume, weather or separation requirements. Under most circumstances an advisory is issued by the ATCSCC whenever NRP procedures are curtailed.
Participation in NRP is voluntary and the process is outlined in FAA Advisory Circular 90-91h. For more information go to http://www.faa.gov/ and click on 'Advisory Circular'.
FEAs and FCAs are developed on an ad hoc basis. They are both three-dimensional volumes of airspace, along with flight filters and a time interval, used to identify flights. They may be drawn graphically, around weather, or they may be based on a NAS element such as a VORTAC. They are used to evaluate demand on a resource.
The difference between an FEA and an FCA is that a Flow Evaluation Area is simply under study while a Flow Constrained Area requires action to address a particular situation.
The only way a pilot will know about an FEA/FCA is through a route advisory indicating the impact area as an FCA. A flight may fly through an FCA if it is not one of the “filtered flights” that has been designated to remain clear of the airspace. If a flight is one of the “filtered flights” it will receive a route that remains clear of the FCA. At this time, only authorized government users and Collaborative Decision Making (CDM) participants have access to viewing FEAs and FCAs.
In many cases, FCAs become Airspace Flow Programs (AFPs). Learn more.
“Capping” is a colloquialism for planning to hold aircraft at altitudes lower than their requested altitude until they are clear of a particular area. It may be in response to weather or other situations that have impacted ATC’s ability to provide service and it may be applied to the entire route of flight. It is used during constrained situations in the National Airspace System and enables aircraft to continue to depart while remaining “underneath” constrained airspace.
A pilot will know that he is being capped when the air traffic controller advises in the clearance to “expect” a final altitude lower than the requested altitude,
based on the appropriate altitude for the direction of flight.
Each pilot in command has the option to refuse a clearance for safety reasons. If a clearance cannot be complied with, the pilot is required to advise ATC. At that time, different options may be presented, including the option of taking a delay on the ground until the situation in the airspace is resolved.
“Tunneling” is a colloquialism for descending traffic prior to the normal descent point at an arrival airport to remain clear of an airspace situation on the route of flight. It is used to avoid conflicting flows of traffic and holding patterns.
A pilot will know that he is being subjected to tunneling if he is descended prior to the normal descent point for the destination airport.
A related technique is called "tower-enroute". Tower enroute is a situation where the aircraft never reaches the enroute stratum, but stays in the lower terminal altitudes being handed-off from tower to tower instead of from center to center. This sometimes reduces delays, especially if the higher enroute stratum is congested.
Integrated Collaborative Rerouting (ICR) is a process that builds on Flow Evaluation Area/Flow Constrained Area (FEA/FCA) capabilities used to reroute aircraft around enroute constraints, incorporating Customer preferences where possible.
The general idea is:
- Traffic Flow Management (TFM) shares constraint information as early as possible via a Planning Route Advisory
- Customers analyze reroute options around the defined constraint and submit preferred routes via Early Intent (EI) messages
- TFM evaluates system impacts of EI preferences
- TFM addresses impacts using preferred EI routes when possible, and if necessary, issues required routes for other affected flights
The benefits of ICR are as follows:
- Customers have more input regarding how their flights are rerouted
- Customers can be more proactive in planning for weather events, other constraints, restrictions, etc.
- Customers have better understanding of alternatives acceptable to Traffic Flow Management
- Customers make fewer exception requests for TFM to handle
- TFM have fewer flights to reroute and do fewer tactical reroutes
- TFM receives earlier feedback on impact of reroutes to Controllers and sectors
- Better traffic predictability
LAADR is a procedure whereby flight altitudes may be limited to flight level 230 and below. LAADR procedures are primarily used in the departure phase of flight, but can be extended for an entire flight when operational benefits are achieved.
The ATCSCC will normally publish, via advisory, the use of LAADR after the Planning Team Telcon (PT). Pilots may contact their local ATC facilities to see if LAADR procedures are applicable. This procedure may be assigned to a flight and, if so, the pilot will be informed to expect an altitude lower than the requested altitude.
For short flights, the procedure may be applied for the entire route. For long flights, the pilot will be given a point to expect a higher altitude.