MART Vol. II MO/MP - NESA - Civil Air Patrol

3.4 Reduced VisibilityAccording to FAA regulations, under almost all circumstances flight usingvisual flight rules can only be conducted with at least three miles of visibility(CAPR 60-1 states the minimum flight visibility of three statute miles is requiredfor all VFR flights unless the PIC is a current and qualified instrument pilot). Ifclouds cover more than one-half the sky, the cloud bases must be no lower than1,000 feet above the terrain. In addition, search aircraft must usually remain atleast 500 feet below the cloud deck.One of the most common hazardous-weather problems is loss of visibility.This can happen either suddenly or very insidiously, depriving the pilot of hisability to see and avoid other aircraft, and reducing or depriving him altogether ofhis ability to control the aircraft, unless he has had training and is proficient ininstrument flying. In reduced visibility, the crew's ability to see rising terrain and toavoid towers, power transmission lines, and other man-made obstacles isdiminished.Visibility may be reduced by many conditions including clouds, rain, snow,fog, haze, smoke, blowing dust, sand, and snow. A similar condition called “whiteout” can occur where there has been snowfall.In most regions of the country, fog and haze are the most common weatherconditions that cause reduced visibility. Fog, especially dense fog, can pose ahazard to even the most sophisticated military or civilian aircraft. In thick fog,reduced visibility may make it extremely difficult, if not impossible, to see landingrunways or areas. The crew should be alert for a potential problem with fogwhenever the air is relatively still, the temperature and dew point are withinseveral degrees, and the temperature is expected to drop further, as aroundsunset and shortly after sunrise. This is often a factor in delaying the first sortiesof the day.Haze, a fine, smoke-like dust causes lack of transparency in the air. Its mostoften caused when still air prevents normal atmospheric mixing, allowing theparticles to persist, instead of the wind's dispersing them. Like fog, it is most likelyto occur when the air is still. The air doesn't mix to scatter the particles of dust,smoke, or pollen. If the wind remains calm for several days, visibility will becomeprogressively worse. This atmospheric condition is most common in heavilypopulated, industrialized areas of the country; it can also be present anywherethere is still air and a source of particles, like near burning farm fields or thickforests that produce large quantities of pollen. It is especially noticeable in theearly morning. Haze can cause your eyes to focus on a point 10-30 feet ahead.Frequently, as the sun warms the cool, hazy air and causes it to expand andrise, visibility at the surface will improve and appear acceptable. What initiallyappeared to be ample visibility can, after takeoff, become almost a completeobstruction to lateral or forward visibility several hundred feet above the surface.Downward visibility is satisfactory, but pilots may feel apprehensive about the lossof a visible horizon to help judge aircraft control, and about what might come outof the murk ahead. Visibility at this altitude may actually be more than theminimum three miles, yet the pilot may interpret this visual range as a wall justbeyond the airplane's nose.In summer, haze and smoke may extend upward more than 10,000 feetduring the heat of the day, hiding rain showers or thunderstorms within the hazeand presenting a special hazard. When haze and smoke are present, the bestmeasure a flight crew can take to minimize risk of such an encounter is to get a54