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36 place the sprayer in the cab so it is available while they are snow as compared to a high-straight mold board with a snow plowing. deflector, according to snow equipment drivers. But low-center mold boards are not useful at airports that routinely experience Wiper blades are an important factor in keeping the wind- high volumes of snow. When used, snow deflectors with trap shield clean for clear visibility. However, the equipment angles less than 50 degrees can eliminate much of the blow- manufacturers stated they provide only a heavy-duty winter back (51). Vehicle speed is another factor affecting the amount blade that is often no different than what one can obtain for of swirling snow and resulting snow cloud around the vehicle. a private vehicle. As a result, ice and snow can still accumu- The slower the speed, the less the blow-back. Unfortunately, late on them causing ineffective wiping action and viewing the slower the speed, the longer a vehicle remains on the move- distortion. Older vehicles used to have ridges etched into the ment areas as a potential hazard to aircraft. glass as a way to vibrate the blade to help it shed snow and ice. Several respondents implied that heated wiper blades The design of the cabin layout has an impact on driver were of value, but the most common request from respon- fatigue and distractions. Equipment manufacturers are work- dents was for better wiper blades overall. ing to place controls in easy and comfortable reach of the operator. Mounting the controls on a console attached to the "While following the brooms at such slow speeds (they seat provides ergonomic benefits. Sound deadening material are 10 mph tow-behinds), the windshield on the opera- is being added in some vehicles to better reduce the decibel tions vehicle can get iced up to the point where the wipers readings in the cabin. Because of the long periods of sitting, don't do anything. The side windows of the broom's the comfort of the seat is of importance. Most seats installed tow vehicles also get snow-covered." in snow removal equipment are made of varying stiffness of "While not one of the above-listed areas, it is helpful to foam, but air-inflated seat cushions are being researched as check vehicle windshields before each snow season, an alternative to reduce fatigue and increase comfort (52). especially when using sand. The pitted windshields Most newly purchased vehicles come equipped with air- should be replaced, as necessary, to provide better visi- adjustable mechanisms. bility for the next winter season." Windows can be kept clear of frost, snow, or ice accumu- SNOW REMOVAL EQUIPMENT lation through the use of defroster systems, either electrical or hot air venting. The preference leans toward electrically Advisory Circular 150/5200-30, Airport Winter Safety and heated windows and mirrors. Defroster systems can add to Operations, provides guidance in the number and type of vehi- humidity buildup inside the cab as a result of the driver's cles and appliances for the airport size and operation (12). breathing and body heat. Some airport operators have speci- Sizing of the snow and ice control equipment fleet should be fied air conditioning units on snow removal equipment for based on the total Priority 1 paved area that must be cleared eliminating moisture in the cabin. If not properly designed, of snow, slush, or ice within a recommended clearance time. defroster systems can contribute to driver fatigue through the Priority 1 paved areas amount to having cleared one primary generation of excessive noise or fluctuating cabin tempera- runway, taxiway access and egress from that runway to the tures, and electric wires in the windshield can malfunction. terminal, and any ARFF access routes. The equipment fleet recommended in the advisory circular is associated with Good lighting and good defrosting are key components eligibility for federal funding participation. for increasing visibility. Another influential factor is the height of the cabin. Plows and sweepers generate swirling or Formulas exist for determining the number of plows, blow-back snow over any attachments and onto the vehicle brooms, and blowers to achieve the clearance time necessary windshield. As one airport operator mentioned, being able to for a particular runway or other paved surface areas (53, 54). sit up high and look out and over the swirling snow makes a The acquisition of larger capacity snow and ice removal big difference in his ability to see where he is plowing and to equipment can help reduce the potential for incursion by hav- see objects such as signs, markings, and aircraft. The popu- ing fewer exposed numbers of operations (55). However, larity of vehicles with the cabins placed as far forward as pos- financial considerations may preclude the ability of an airport sible and the engines mounted beneath or behind the cabin to acquire more efficient or larger pieces of equipment. Advi- support this idea and have environmental noise reduction as sory Circular 150/5220-20, Airport Snow and Ice Control an added benefit. Equipment, offers guidance on how to select the number and types of equipment necessary to meet recommended clear- Associated with the generation of swirling or blow-back ance times (54). snow ("snow cloud" effect) is the design of the plow blade and deflectors, and the speed capability of the vehicle. All three The design of vehicles and attachments, the layout and affect the extent to which snow is blown up and over the equipping of cabins, and the placement of lights all have an blade or brooms and impedes forward visibility. A low-height impact on the prevention of incursions. The impact has not mold board on a plow reduces the amount or height of swirling been adequately evaluated to identify the best method or