Other En Route Tools

North American Route Program (NRP)

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 airports.

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 90-91K.

Flow Evaluation Area/Flow Constrained Area (FEA/FCA)

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 about AFPs.

Capping

“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

“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)

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

Low Altitude Alternate Departure Routing (LAADR)

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.