What does an asterisk (*) before an altitude along a low altitude airway signify?

The presence of an asterisk (*) before an altitude along a low altitude airway indicates the Minimum Obstruction Clearance Altitude (MOCA). MOCA is specifically designed to provide the lowest altitude that assures obstacle clearance for aircraft within a defined lateral distance from the centerline of an airway, typically within 22 nautical miles from a VOR. This designation is crucial for pilots, as it ensures safe navigation by minimizing the risk of collisions with terrain or obstacles, particularly in areas where higher altitudes may not be feasible or required.

Understanding the MOCA is essential for effective route planning and in-flight navigation, especially in terrain-heavy regions. While the other options refer to different types of altitudes used in aviation charts and procedures, they do not specifically align with the use of an asterisk in this context. For instance, minimum sector altitude pertains to a defined area surrounding a navigational aid; initial approach altitude is related to the altitude for beginning the approach phase; and maximum altitude is simply the highest altitude permitted along that airway, none of which share the same specific functionality or indication as MOCA.