We spoke to experts - Trev and Dave from Edale Mountain Rescue Team - about how to navigate in low visibility. So are the cloudier days, and the low sun. On such occasions the pilot may be led into a false sense of security, and on descending into the haze layer suddenly find that their visibility is much reduced.Autumn's rolling in. ![]() When a pilot is flying above a low-level haze layer (which may affect the surface), the pilot will often be able to see further than the reported airfield visibility. The pilot flying in the haze layer does not perceive the visibility to be as good as reported. Pilots who are not qualified to use instruments, or flying poorly equipped aircraft, may become disorientated when confronted with poor visibility and/or low cloud.Įlevated layers of haze can mislead pilots, since reported (and correct) values of visibility are those assessed horizontally at the surface. That obstacle may be natural (hill, or simply the ground), a structure (building/tower), or another aircraft. When cloud base and/or visibility fall below acceptable values, the pilot is in a situation where there will not be sufficient time to take avoiding action should an obstacle be sighted. Conversely, reductions to visibility can and often do affect very large areas and as such dealing with the problem can be much more difficult. Under such circumstances a pilot may be able to ‘navigate around’ the problems. Poor visibility may likewise only affect small areas (in the form of showers, or in fog patches), and may be caused for many reasons (rain, mist, haze, smoke etc.). That noted, even a small patch of low cloud may cover a small peak (indeed may be caused by the peak). As cloud amounts increase, then the risk to aircraft also increases. 1 or 2 oktas) may not generally be hazardous. Whilst the precise values may differ under the many varied possibilities, perhaps low cloud and poor visibility might best be described as having values that fall below the operating minima of either or both that of the aircraft and pilot. They are also quite difficult to define since they will depend upon aircraft type, pilot skill and experience, the precise role the aircraft is performing, and the navigation aids available en route or at the departure/destination/alternate airfields. Low cloud and poor visibility may be overlooked as being potentially hazardous. ![]() However, when descending onto the approach, and trying to view the airfield at a slant angle through the fog, the pilot may very quickly lose all visual cues and find themselves in very serious difficulty. Pilots may be given a false sense of security when over-flying an airfield, since structures and runways may be quite clear to the pilot when looking down from directly above the airfield. Ice fog has similar visibility restrictions, but in addition untreated taxiways and runways may be coated with a thin layer of ice. Even allowing for the technical ability, airline and military procedures may prohibit ‘auto landings’ under certain conditions. Only the most sophisticated of aircraft (Civil Airliners/military aircraft) may be able to ‘auto land’ under such circumstances, and then only at suitably equipped airports. If the fog layer is less than 2 metres deep over land it is termed shallow fog.įog seriously degrades visibility to such a degree that landing may be impossible. Hill fog and frontal fog are also descriptors commonly used.įog may cover a large, continuous area or it may form in patches possibly only covering small parts of an airfield. For aviation purposes, it is a condition that the horizontal visibility due to such phenomena is reduced to less than 1000 m.įog may be further classified as being formed by advective processes or radiative cooling processes. Fog is the suspension of microscopic droplets of water with diameter approximately 10 µm or less, or in the case of ice fog, particles of ice.
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