NDB Approach
NDB stands for Non-Directional Beacon and an NDB approach is one based on the use of ADF (Automatic Direction Finding) equipment fitted in the aircaft that gives the relative bearing of the beacon. It is a non-precision approach, has limitations and is usually found at minor airports, although some major airports still have them. Due allowance must be made for signal limitations, especially when there is thunderstorm activity. As far as the airport operator is concerned they have a cost advantage as they do not need to be calibration tested, as is the case with ILS (Instrument Landing System) approaches. I could go on, but I hope this gives an outline.