Various natural phenomena can result in sufficient difference of potential between an aircraft in flight and its very rapidly changing surroundings that, immediately adjacent to the aircraft extremities, there will exist potential gradients high enough to produce local atmospheric ionisation or “corona”.

Since there is no effective method known to prevent the development of these potential differences, aircraft are commonly fitted with a number of so-called “static dischargers” or “neutralisers” to control the nature and occurrence positions of the corona in such a way as to minimise the generation and radiation of RF noise, which would otherwise be quite capable of causing complete mis-function of navigational aid systems.