What is the purpose of the Minimum Obstruction Clearance Altitude (MOCA)?

The Minimum Obstruction Clearance Altitude (MOCA) serves a critical function in aviation safety, primarily focusing on guaranteed obstacle clearance and navigational reliability. One of its key roles is to provide a minimum altitude over which aircraft can fly safely, ensuring a clearance of at least 1,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the airway centerline.

In terms of navigation, MOCA ensures that pilots can reliably receive navigation signals within 22 nautical miles of the nearest navigational aid. This distance is significant because it allows pilots to navigate safely and efficiently, ensuring that they remain clear of obstacles and have adequate access to navigation signals, which is particularly important in less populated or mountainous regions where terrain hazards may be present.

The other choices do not accurately define MOCA's primary purpose. The mention of ensuring a minimum clearance of 500 ft over mountains relates more specifically to different regulations or altitudes, not MOCA specifically. Terrain clearance during approach pertains to approach procedures, not the broader definition of MOCA. Lastly, establishing an altitude for VFR flights does not align with the primary function of MOCA, which is geared toward instrument-flight operations and obstacle clearance.