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Aviation Learning Center Document Night Flying Tips
Author: Adrian Eichhorn Date: November 2005
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Terrain - How Do I Avoid It?
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Avoiding terrain at night is easier if altitudes shown on VFR and IFR charts are used as part of your preflight planning.

  • VFR Charts show Maximum Elevation Figures (MEFs). The Maximum Elevation Figures shown in quadrangles bounded by ticked lines of latitude and longitude are represented in THOUSANDS and HUNDREDS of feet above mean sea level. MEFs are determined by rounding the highest known elevation within the quadrangle, including terrain and obstruction (trees, towers, antennas, etc) to the next 100 foot level. These altitudes are then adjusted upward between 100 to 300 feet. Recognize that this practice could give as little as 101 feet of obstacle clearance.

  • IFR enroute low altitude charts contain Off Route Obstruction Clearance Altitudes (OROCA). On the IFR enroute low altitude chart, the Off Route Obstruction Clearance Altitude (OROCA) guarantees 1,000 foot obstacle clearance in non-mountainous terrain and can be used at night to ensure obstacle clearance. In mountainous terrain, this altitude offers 2,000 feet of obstacle clearance.

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