FAA - Clearances

The Clearance dataset provides information about the highest terrain or obstacle elevation within a quadrant or bin on a chart. Clearance values can be used to determine the lowest recommended altitudes that can be flown within a bin or quadrant when taking terrain and obstacle data into account. Depending on the type of clearance and location of the bin, additional buffers may be used in the calculation. The quadrant or bin sizes vary from product to product. Clearance information is published every 56 days by the U.S. Department of Transportation, Federal Aviation Administration – Aeronautical Information Services. Types of clearance data include: Off Route Obstruction Clearance Altitude (OROCA) OROCAs are depicted on the Enroute (IFR) chart series. They include a 1000 foot vertical buffer over the highest terrain or obstacle feature in non-mountainous areas and a 2000 foot vertical buffer in designated mountainous area within the United States. These values include a horizontal buffer of 4 NM in all directions outside of the bin. Off Route Terrain Clearance Altitude (ORTCA) ORTCAs are shown on the Enroute (IFR) chart series. ORTCAs are depicted for charted areas in Mexico and the Caribbean that are located outside the U.S. Air Defense Identification Zone (ADIZ). ORTCAs include a 3000 foot vertical buffer over the highest terrain or obstacle feature. These values include a horizontal buffer of 4 NM in all directions outside of the bin. Maximum Elevation Figure (MEF) – Future Enhancement MEFs are depicted on the Visual (VFR) chart series. MEF values include a 100 foot buffer over the highest obstacle feature and a 300 foot buffer over the highest terrain feature in each bin, and are then rounded up to the next 100 foot value. There is no horizontal buffer included in the MEF calculation.