When is coastal error minimized when taking ADF bearings close to the coast?

Coastal error is a phenomenon that occurs when taking ADF (Automatic Direction Finder) bearings near the coast. This error arises due to the differing propagation properties of radio waves over land and water, which can lead to inaccurate bearings if the aircraft is too close to the shoreline.

Minimizing coastal error is most effectively accomplished when the ADF bearing to the beacon crosses the coastline at right angles. This configuration ensures that the bearing is less influenced by the different characteristics of the terrain on either side of the coast. When the bearing crosses perpendicularly, it minimizes the effect of any refraction or discrepancies in signal that can occur due to the transition from water to land and vice versa.

In scenarios where the beacon is far from the coast or when the aircraft is flying parallel to the coastline, the potential for increased coastal error grows, as the bearings may become skewed by the land's varying influence. Similarly, a bearing that crosses the coastline at an obtuse angle may still be affected by these discrepancies, leading to less accurate positioning. Thus, the optimal approach is to have the bearing intersect the coastline at right angles to ensure the highest accuracy in navigation.