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charts for the United States government.
En route high-altitude charts provide aeronautical information
for en route instrument navigation (IFR) 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 NACG 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 NACG 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, 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 indicates Class C and D airspace,
respectively, per Figure 8-3.
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 NACG 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 NACG
charts by a leading asterisk (e.g., “*3400”—see Figure 8-2,
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 will only extend to the MRA or above.
However, if the aircraft is equipped with distance measuring
equipment (DME) and the chart indicates the intersection can
8-7
Figure 8-3. En Route Airport Legend.
be identified with such equipment, the pilot could define the
fix without attaining the MRA. On NACG charts, the MRA
is indicated by the symbol and the altitude preceded by
“MRA” (e.g., “MRA 9300”). [Figure 8-2]
The minimum crossing altitude (MCA) will be 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 NACG charts, the MCA is indicated by the
symbol , and the Victor airway number, altitude, and
the direction to which it applies (e.g. “V24 8000 SE”).
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