July 1, 2004
By Bruce Landsberg
This section provides night VFR pilots or pilots in areas of less-than-good visibility with a procedure to avoid Controlled Flight Into Terrain (CFIT). Plan the enroute portion of your flight to be at or above the altitudes shown below to avoid terrain or towers. Remember: Ceilings must be at least 500 feet above your cruising altitude when in Class E airspace.
Within the quadrangles of latitude and longitude shown on this IFR enroute low altitude chart the Off Route Obstruction Clearance Altitude (OROCA) is 3,500 feet. This altitude guarantees 1,000-foot obstacle clearance in non-mountainous terrain and can be used at night or when visibility is reduced to ensure obstacle clearance.
The Minimum Enroute Altitude (MEA) highlighted on this chart is 6,000 feet. This altitude meets obstacle clearance requirements and provides acceptable ground based navigation signal coverage.
The minimum obstruction clearance altitude (MOCA) highlighted is 3,000 feet. On NACO charts this altitude is shown with an *. MOCA is the lowest altitude between two fixes that meets obstacle clearance requirements. This altitude only assures an acceptable ground based navigation signal within 22 nautical miles of a VOR. Satellite based navigation systems, like GPS, will still receive navigation signals at these altitudes. OROCAs, MEAs, and MOCAs are found on IFR enroute low altitude charts.
Try the AOPA Air Safety Foundation's Obstacle Clearance safety quiz to test your new skills. View the AOPA Air Safety Foundation's Safety Brief on Terrain Avoidance (PDF file — 178KB).
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