GHI vortac  IJK vortac (L) HIJ vortac  V-204  V-204  30  70  Obstacle study flight  inspection and ESV’s  required  GHI vortac  IJK vortac (L)  HIJ vortac (shutdown)  SUB-ROUTE V-204  60*  90  Figure 2-18 Sub-route wider than existing route.  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 air-  space. [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.  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.  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.  The graphic depiction of TEC routes located in the CS is not  to be used for navigation or for detailed flight planning  because not all city pairs are depicted. The information  is intended to show geographic areas connected by TEC.  [Figure 2-19] Pilots should refer to the route descriptions  for specific flight planning.  As shown in Figure 2-20, the route description contains four  columns of information. The first column is the approach  control area within which the departure airport is located,  which are listed alphabetically. The second column shows  the specific route, airway, or radial that is to be used.  The third column shows the highest altitude allowed for  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  Tower En Route Control Route Descriptions  Tower En Route Control  2-10 