IFR En Route Charts (Part One) Airport Information and Charted IFR Altitudes

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.

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

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., see below) indicates Class C and D airspace, respectively, per Figure 1-3.

Figure 1-3. En route airport legend.

Figure 1-3. En route airport legend. [click image to enlarge]

Charted IFR Altitudes

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.

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 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 fix without attaining the MRA. On AeroNav Products charts, the MRA is indicated by the symbol (shown below) and the altitude preceded by “MRA” (e.g., “MRA 9300”). [Figure 1-2]

Figure 1-4. Legend from en route low attitude chart, air traffic services and airspace information section.

Figure 1-4. Legend from en route low attitude chart, air traffic services and airspace information section. [click image to enlarge]

The minimum crossing altitude (MCA) is charted when a higher MEA route segment is approached. The MCA is usually indicated when a pilot is approaching steeply rising terrain and obstacle clearance and/or signal reception is compromised. In this case, the pilot is required to initiate a climb so the MCA is reached by the time the intersection is crossed. On AeroNav Products charts, the MCA is indicated by the symbol (see below) , and the Victor airway number, altitude, and the direction to which it applies (e.g. “V24 8000 SE”).

The maximum authorized altitude (MAA) is the highest altitude at which the airway can be flown with assurance of receiving adequate navigation signals. Chart depictions appear as “MAA-15000.”


When an MEA, MOCA, and/or MAA change on a segment other than at a NAVAID, a sideways “T” (shown below) is depicted on the chart. If there is an airway break without the symbol, one can assume the altitudes have not changed (see the upper left area of Figure 1-2). When a change of MEA to a higher MEA is required, the climb may commence at the break, ensuring obstacle clearance. [Figure 1-4]

Figure 1-5. Legend from en route low attitude chart.

Figure 1-5. Legend from en route low attitude chart. [click image to enlarge]


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