MEA 、MOCA和Enroute MORA的区别

参考资料：

MINIMUM ENROUTE ALTITUDE (MEA)

The MEA is listed as a number, e.g. 6500, along the airway and is the lowest altitude between radio fixes that assures navigational signal coverage (not necessarily two way voice communication) and meets obstacle clearance requirements between the fixes. The clearance is 1000 ft in non mountainous areas, 2000 ft in mountainous areas, and includes the airspace within plus or minus 4 nm of the airway centerline.

Altitudes for IFR flight usually are in accord with the hemispherical rule of odd altitudes for magnetic courses of 0° - 179° and even altitudes for magnetic courses of 180°-359°. An easy way to remember the rule is WEEO - West evens; East odds. ATC may assign altitudes that do not correspond to the rule, however.

Some route may have a gap in the navigation signal. This is designated as MEA GAP on NOS charts and by a broken bar on the Jepp charts. MEAs may also be directional, based on the travel from high ground to low or low to high. A bar crossing the airway at an intersection indicates a change in MEA. You are not required to increase your altitude until crossing the intersection, unless a minimum crossing altitude (MCA) is specified.

MINIMUM OBSTRCTION CLEARANCE ALTITUDE (MOCA) 

The MOCA is the lowest altitude in effect between fixes which meets the obstacle clearance requirements for the entire segment. Navigational signals are assured only within 22 nm of the VOR. If the MOCA is different than the MEA, it is indicated by an asterisk on NOS charts (*3500) and a "T" on the Jepps (3500T). If the MOCA and MEA are the same, no indication is made on the charts.

       通过看以上资料和查书，可以看出MEA和MOCA相同的地方是都要保证具备在平原地区300米的超障余度和山区600米的超障余度。不同的地方在于MEA需要保证在整个航段中都要有无线电导航信号覆盖，而MOCA则只保证在VOR台附近22海里范围内有无线电导航信号覆盖。

       MEA和Enroute MORA的区别是：MEA是保证定位点或者航路中心线4海里以内的区域满足超障余度的要求，而Enroute MORA是要保证定位点或中心线10海里以内的区域满足超障余度要求。

      此外，还有网格最低偏航高度Grid MORA，它与Enroute MORA的定义内容基本相同，即保证一定范围内的区域满足规定的超障余度（杰普逊中规定是：最高标高障碍物在5000英尺及以下超障余度为1000英尺，在5001英尺及以上超障余度为2000英尺；国内法规规定为山区超障余度600米，其他地区超障余度300米）。两者不同之处是Enroute MORA针对的是航路中心线或定位点十海里以内的区域，而Grid MORA针对的是经纬网格内的区域。