An Obstacle Clearance Area (OCA) is a designated volume of airspace within which aircraft are guaranteed a minimum vertical or lateral separation from terrain and obstacles. These areas are part of the design of instrument flight procedures (IFPs) and ensure that aircraft operating under IFR remain safe from terrain or obstacles, even during low visibility or non-precision approaches.
OCAs are calculated and protected by procedure designers following ICAO PANS-OPS or TERPS criteria, depending on the region.

• Ensure safe obstacle clearance during all phases of instrument flight
• Define minimum altitudes and flight paths for approach, missed approach, departure, and enroute segments
• Provide structure for charting approach minima, including MDA, DA, and OCH

• OCH: The lowest height above the airport elevation at which obstacle clearance is guaranteed
• MDA/DA: The published minimum altitude a pilot may descend to on approach

OCH is used to calculate MDA/DA based on aircraft category and required visibility.

These areas are centered on the runway threshold and assume a bank angle and maneuvering speed.

OCAs themselves are not shown directly, but their limits determine:

• Minimum sector altitudes (MSAs)
• Minimum safe altitudes (MSAs)
• Approach minima (MDA/DA/OCH)
• Obstacle symbols and contouring

• ✅ Understand that MDA/DA includes built-in obstacle clearance
• ✅ Remain within protected areas (especially during circling or visual segments)
• ✅ Do not descend below MDA/DA unless required visual references are in sight
• ✅ Use LearnATC to practice approaches with varying terrain and OCH calculations