En Route Operations (Part Three)

Preferred IFR Routes

Preferred IFR routes are established between busier airports to increase system efficiency and capacity. They normally extend through one or more ARTCC areas and are designed to achieve balanced traffic flows among high density terminals. IFR clearances are issued on the basis of these routes except when severe weather avoidance procedures or other factors dictate otherwise. Preferred IFR routes are listed in the CS and can also be found on www.fly.faa.gov, which requires entering the following data: departure airport designator, destination, route type, area, aircraft types, altitude, route string, direction, departure ARTCC, and arrival ARTCC. [Figure 2-14]


If a flight is planned to or from an area having such routes but the departure or arrival point is not listed in the CS, pilots may use that part of a preferred IFR route that is appropriate for the departure or arrival point listed. Preferred IFR routes are correlated with departure procedures (DPs) and STARs and may be defined by airways, jet routes, direct routes between NAVAIDs, waypoints, NAVAID radials/ distance measuring equipment (DME), or any combinations thereof.

Figure 2-14. Chart Supplement (includes Airport/Facility Directory section).

Figure 2-14. Chart Supplement (includes Airport/Facility Directory section).

Preferred IFR routes are published in the CS for the low and high altitude stratum. If they begin or end with an airway number, it indicates that the airway essentially overlies the airport and flights normally are cleared directly on the airway. Preferred IFR routes beginning or ending with a fix indicate that pilots may be routed to or from these fixes via a SID route, radar vectors, or a STAR. Routes for major terminals are listed alphabetically under the name of the departure airport. Where several airports are in proximity, they are listed under the principal airport and categorized as a metropolitan area (e.g., New York Metro Area). One way preferred IFR routes are listed is numerically, showing the segment fixes and the direction and times effective. Where more than one route is listed, the routes have equal priority for use. Official location identifiers are used in the route description for very high frequency omnidirectional ranges (VORs) and very high frequency omnidirectional ranges/ tactical air navigation (VORTACs), and intersection names are spelled out. The route is direct where two NAVAIDs, an intersection and a NAVAID, a NAVAID and a NAVAID radial and distance point, or any navigable combination of these route descriptions follow in succession.

A system of preferred IFR routes helps pilots, flight crews, and dispatchers plan a route of flight to minimize route changes, and to aid in the efficient, orderly management of air traffic using Federal airways. Preferred IFR routes are designed to serve the needs of airspace users and to provide for a systematic flow of air traffic in the major terminal and en route flight environments. Cooperation by all pilots in filing preferred routes results in fewer air traffic delays and better efficiency for departure, en route, and arrival air traffic service. [Figure 2-15]

Figure 2-15 Preferred IFR routes.

Figure 2-15 Preferred IFR routes. [click image to enlarge]

Substitute Airway or Route Structures

ARTCCs are responsible for specifying essential substitute airway or route segments (sub-routes) and fixes for use during scheduled or unscheduled VOR/VORTAC shutdowns. Scheduled shutdowns of navigational facilities require planning and coordination to ensure an uninterrupted flow of air traffic. Aeronautical Information Services, in coordination with the ARTCCs, determine when the length of outages or other factors require publication of sub-routes and Flight Program Operations (AJW-3) provides flight inspection services, obstacle clearance verification, certification, and final approval of substitute routes.


Substitute Airway En Route Flight Procedures

A schedule of proposed facility shutdowns within the region is maintained and forwarded as far in advance as possible to enable the substitute routes to be published. Substitute routes are normally based on VOR/VORTAC facilities established and published for use in the appropriate altitude strata. In the case of substitute routes in the upper airspace stratum, it may be necessary to establish routes by reference to VOR/VORTAC facilities used in the low altitude system. Non-directional (radio) beacon (NDB) facilities may only be used where VOR/VORTAC coverage is inadequate and ATC requirements necessitate use of such NAVAIDs. Where operational necessity dictates, NAVAIDs may be used beyond their standard service volume (SSV) limits that define the reception limits of unrestricted NAVAIDs, which are usable for random/unpublished route navigation, provided that the routes can be given adequate frequency protection.

Figure 2-16 14 CFR Part 95 sub-routes.

Figure 2-16 14 CFR Part 95 sub-routes. [click image to enlarge]

The centerline of substitute routes must be contained within controlled airspace [Figure 2-16], although substitute routes for off-airway routes may not be in controlled airspace. [Figure 2-17] Substitute routes are flight inspected to verify clearance of controlling obstacles and to check for satisfactory facility performance. If substitute routes do not overlie existing routes, or are wider than existing routes, map studies are required to identify controlling obstacles. [Figure 2-18] The format for describing substitute routes is from navigational fix to navigational fix. A minimum en route altitude (MEA) and a maximum authorized altitude (MAA) are provided for each route segment. Temporary reporting points may be substituted for the out-of-service facility and only those other reporting points that are essential for ATC. Normally, temporary reporting points over intersections are not necessary where Center radar coverage exists. A minimum reception altitude (MRA) is established for each temporary reporting point.

Figure 2-17 Non-Part 95 sub-routes.

Figure 2-17 Non-Part 95 sub-routes. [click image to enlarge]

Figure 2-18 Sub-route wider than existing route.

Figure 2-18 Sub-route wider than existing route. [click image to enlarge]


Tower En Route Control

Tower en route control (TEC) is an ATC program available to pilots that provides a service to aircraft proceeding to and from metropolitan areas. It links designated approach control areas by a network of identified routes made up of the existing airway structure of the NAS, which makes it possible to fly an IFR flight without leaving approach control airspace. [Figure 2-19] This service is designed to help expedite air traffic and reduces ATC and pilot communication requirements. The program is generally used by non-turbojet aircraft operating at and below 10,000 feet but a few facilities, such as Milwaukee and Chicago, have allowed turbojets to proceed between city pairs. Participating flights are relatively short with a duration of two hours or less.

Figure 2-19. Tower En Route Control (TEC) Northeast U.S. (Eastern).

Figure 2-19. Tower En Route Control (TEC) Northeast U.S. (Eastern). [click image to enlarge]

TEC is referred to as tower en route, or tower-to-tower, and allows flight beneath the en route structure. TEC reallocates airspace both vertically and geographically to allow flight planning between city pairs while remaining with approach control airspace. All users are encouraged to use the TEC route descriptions located in the CS when filing flight plans. [Figure 2-20] All published TEC routes are designed to avoid en route airspace, and the majority is within radar coverage.

Figure 2-20. Chart Supplement (NE), Tower En Route Control route descriptions (Baltimore).

Figure 2-20. Chart Supplement (NE), Tower En Route Control route descriptions (Baltimore). [click image to enlarge]