Within the NAS it is possible to fly an IFR flight without leaving approach control airspace, using tower en route control (TEC) service. This helps expedite air traffic and reduces air traffic control and pilot communication requirements. TEC is referred to as “tower en route,” or “tower-to-tower,” and allows flight beneath the en route structure. Tower en route control 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 in the Airport/Facility Directory when filing flight plans. All published TEC routes are designed to avoid en route airspace, and the majority are within radar coverage. [Figure 3-4]

The graphic depiction of TEC routes is not to be used for navigation or for detailed flight planning. Not all city pairs are depicted. It is intended to show geographic areas connected by tower en route control. Pilots should refer to route descriptions for specific flight planning. The word “DIRECT” appears as the route when radar vectors are used or no airway exists. Also, this indicates that a SID or STAR may be assigned by ATC. When a NAVAID or intersection identifier appears with no airway immediately preceding or following the identifier, the routing is understood to be direct to or from that point unless otherwise cleared by ATC. Routes beginning and ending with an airway indicate that the airway essentially overflies the airport, or radar vectors will be issued. Where more than one route is listed to the same destination, ensure that the correct route for the type of aircraft classification has been filed. These are denoted after the route in the altitude column using J (jet powered), M (turbo props/special, cruise speed 190 knots or greater), P (non-jet, cruise speed 190 knots or greater), or Q (non-jet, cruise speed 189 knots or less). Although all airports are not listed under the destination column, IFR flights may be planned to satellite airports in the proximity of major airports via the same routing. When filing flight plans, the coded route identifier, i.e., BURL1, VTUL4, or POML3, may be used in lieu of the route of flight.


The present en route system is based on the VHF airway/ route navigation system. Low frequency (LF) and integrated LF/VHF airways and routes have gradually been phased out in the conterminous U.S., with some remaining in Alaska.


VOR, VORTAC, and instrument landing system (ILS) facilities, as well as most nondirectional radio beacons (NDBs) and marker beacons installed by the FAA, are provided with an internal monitoring feature. Internal monitoring is provided at the facility through the use of equipment that causes a facility shutdown if performance deteriorates below established tolerances. A remote status indicator also may be provided through the use of a signal-sampling receiver, microwave link, or telephone circuit. Older FAA NDBs and some non-Federal NDBs do not have the internal feature and monitoring is accomplished by manually checking the operation at least once each hour. FAA facilities such as automated flight service stations (AFSSs) and ARTCCs/sectors are usually the control point for NAVAID facility status. Pilots can query the appropriate FAA facility if they have questions in flight regarding NAVAID status, in addition to checking notices to airmen (NOTAMs) prior to flight, since NAVAIDs and associated monitoring equipment are continuously changing.


Numerous low frequency airways still exist in Alaska, as depicted in this NACO en route low altitude chart excerpt near Nome, Alaska. [Figure 3-5] Colored LF east and west airways G7, G212 (green), and R35 (red), are shown, along with north and south airways B2, B27 (blue), and A1 (amber), all based upon the Fort Davis NDB en route NAVAID. The nearby Nome VORTAC VHF en route NAVAID is used with victor airways V452, V333, V507, V506, and V440.