Tower En Route Control (TEC) is an ATC program that  uses overlapping approach control radar services to provide  IFR clearances. By using TEC, a pilot is routed by airport  control towers. Some advantages include abbreviated filing  procedures and reduced traffic separation requirements. TEC  is dependent upon the ATC’s workload, and the procedure  varies among locales. The latest version of Advisory Circular (AC) 90-91, North  American Route Program (NRP), provides guidance to users  of the NAS for participation in the NRP. All flights operating  at or above FL 290 within the conterminous United States  and Canada are eligible to participate in the NRP, the primary  purpose of which is to allow operators to plan minimum time/ cost routes that may be off the prescribed route structure. NRP  aircraft are not subject to route-limiting restrictions (e.g.,  published preferred IFR routes) beyond a 200 NM radius of  their point of departure or destination. The objective of IFR en route flight is to navigate within the  lateral limits of a designated airway at an altitude consistent  with the ATC clearance. Your ability to fly instruments  safely and competently in the system is greatly enhanced by  understanding the vast array of data available to the pilot on  instrument charts. AeroNav Products maintains and produces  the charts for the U.S. Government. En route high-altitude charts provide aeronautical information  for en route instrument navigation at or above 18,000 feet  MSL. Information includes the portrayal of Jet and RNAV  routes, identification and frequencies of radio aids, selected  airports, distances, time zones, special use airspace, and  related information. Established jet routes from 18,000 feet  MSL to FL 450 use NAVAIDs not more than 260 NM apart.  The charts are revised every 56 days. To effectively depart from one airport and navigate en route  under instrument conditions, a pilot needs the appropriate  IFR en route low-altitude chart(s). The IFR low altitude en  route chart is the instrument equivalent of the sectional chart.  When folded, the cover of the AeroNav Products en route  chart displays an index map of the United States showing the  coverage areas. Cities near congested airspace are shown in  black type and their associated area chart is listed in the box  in the lower left-hand corner of the map coverage box. Also  noted is an explanation of the off-route obstruction clearance  altitude (OROCA). The effective date of the chart is printed  on the other side of the folded chart. Information concerning  MTRs is also included on the chart cover. The en route charts  are revised every 56 days. The minimum reception altitude (MRA) identifies the lowest  altitude at which an intersection can be determined from  an off-course NAVAID. If the reception is line-of-sight  based, signal coverage only extends to the MRA or above.  However, if the aircraft is equipped with distance measuring  equipment (DME) and the chart indicates the intersection can  be identified with such equipment, the pilot could define the  The minimum obstruction clearance altitude (MOCA), as the  name suggests, provides the same obstruction clearance as  an MEA; however, the NAV signal reception is ensured only  within 22 NM of the closest NAVAID defining the route. The  MOCA is listed below the MEA and indicated on AeroNav  Products charts by a leading asterisk (e.g., “*3400”—see  Figure 1-2 , V287 at bottom left). The minimum en route altitude (MEA) ensures a navigation  signal strong enough for adequate reception by the aircraft  navigation (NAV) receiver and obstacle clearance along the  airway. Communication is not necessarily guaranteed with  MEA compliance. The obstacle clearance, within the limits of  the airway, is typically 1,000 feet in non-mountainous areas  and 2,000 feet in designated mountainous areas. MEAs can  be authorized with breaks in the signal coverage; if this is  the case, the AeroNav Products en route chart notes “MEA  GAP” parallel to the affected airway. MEAs are usually  bidirectional; however, they can be single-directional. Arrows  are used to indicate the direction to which the MEA applies. Airport information is provided in the legend, and the  symbols used for the airport name, elevation, and runway  length are similar to the sectional chart presentation.  Associated city names are shown for public airports only.  FAA identifiers are shown for all airports. ICAO identifiers  are also shown for airports outside of the contiguous United  States. Instrument approaches can be found at airports with  blue or green symbols, while the brown airport symbol  denotes airports that do not have instrument approaches.  Stars are used to indicate the part-time nature of tower  operations, Automatic Terminal Information Service (ATIS)  frequencies, part-time or on request lighting facilities, and  part-time airspace classifications. A box after an airport name  with a “C” or “D” inside (e.g.,   ) indicates Class C and D  airspace, respectively, per  Figure 1-3 .  When the AeroNav Products en route chart is unfolded, the  legend is displayed and provides information concerning  airports, NAVAIDs, communications, air traffic services,  and airspace. Airport Information IFR En Route Charts Charted IFR Altitudes 1-6