# NDB Coastal Refraction RNAV

Coastal refraction is an error affecting NDBNDB —Non-Directional Beacon signals as they cross a coastline, travelling towards the sea. The path of the wave will bend towards the coast, caused by the increase in speed of the wave as it crosses the coast. This causes errors at the aircraft the waves arrive from an "incorrect" direction.

The degree of coastal refraction has many factors which affect it, but the main ones to remember are:

1. The angle at which the wave crosses the coast. If this is 90° (perpendicular to the coast), there is no refraction, but the amount of refraction and therefore the error both increase as the angle with the coast becomes more acute.
2. How far inland the NDBNDB —Non-Directional Beacon is. The further inland, the worse the error caused by the refraction.
3. The height of the aircraft. The lower the aircraft is, the worse the effect of coastal refraction will be.