FLIGHT TRAINING PUBLICATION (FLIP) STUDENT GUIDE
Minimum Enroute Altitude (MEA) - The lowest published altitude between radio fixes on
an airway which assures acceptable navigational signal coverage and meets obstacle clearance
requirements between those fixes. The MEA prescribed for a Federal airway or segment thereof
applies to the entire width of the airway segment between the defining radio fixes. In designated
mountainous areas, the MEA has a 2000 feet obstacle clearance requirement and in other areas, a
1000 feet obstacle clearance requirement.
Minimum Obstruction Clearance Altitude (MOCA) - The lowest published altitude in effect
between radio fixes on airways or route segments which meets obstacle clearance requirements
for the entire route segment. MOCA assures acceptable navigational signal coverage only within
22 NM of a NAVAID (VOR/TACAN). In designated mountainous areas, the MOCA has a 2000
feet obstacle clearance requirement and in other areas, a 1000 feet obstacle clearance
Off Route Obstruction Clearance Altitudes (OROCA) - Provides obstruction clearance with a
1000 foot buffer in designated non-mountainous areas and a 2000 foot buffer in designated
mountainous areas within the United States. This altitude is provided for obstruction clearance
only. It does not provide for NAVAID signal or communications coverage.
Minimum Crossing Altitude (MCA) - The lowest altitude at certain radio fixes at which an
aircraft must cross when proceeding in the direction of a higher MEA.
Minimum Reception Altitude (MRA) - The lowest altitude at which signals adequate to
determine the specified VOR/TACAN fixes can be received. This applies to the operation of an
aircraft over an intersection used in air navigation. The MRA is used to help define a fix off
another NAVAID not on the Victor route.
Class B Airspace - Light blue shaded areas on a Low Altitude Chart alert users to the presence
of a Class B airspace. An identification box will specify the maximum altitude. Smaller Class B
airspaces have additional areas around them in which Mode C is required, depicted on the chart
by shaded blue stripes out to a 30 NM radius.
Class C Airspace - Depicted by a light blue shaded circle with a broken outline, out to a 10 NM
Special Use Airspace
The legend includes a section on special use airspace which outlines the AP1/A information
provided on the chart for each area. (Figure 6-10). Only Special Use Airspace that exists
between surface and 18,000 are depicted on the Low Charts.
ENROUTE LOW ALTITUDE AND AREA CHARTS