Abstract:
Safety improvements of airport runways and taxiways are achieved by providing a flexible, water-impermeable surfacing material on a compacted soil base directly adjacent to an edge of airstrip shoulders. A synthetic grass surface is provided on the area beyond the surfacing material so that foreign objects such as loose particles of the airstrip shoulder materials will be driven by jet blasts and run-off across the relatively smooth texture of the surfacing material and will be trapped by the synthetic grass, thereby minimizing foreign object damage to aircraft engines, particularly to those overhanging engines which extend well beyond the existing runway and taxiway shoulders.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to safety improvements for airport taxiways and runways and particularly to the need to increase the width of taxiways and runways at airports in order to minimize the risk of foreign object damage to aircraft engines, as well as the safety issues regarding the deterioration of the existing natural grass surfaces bounding taxiways and runways.  
         BACKGROUND OF THE INVENTION  
         [0002]    With the advent of larger and more powerful planes circulating on airport runways and taxiways that were constructed many years ago, there is a serious safety concern regarding overhanging engines which now frequently extend well beyond the existing runway and taxiway shoulders. The new generation of aircraft presently being manufactured have very large wing spans resulting in the jet engines overlapping the existing runway and taxiway shoulders, and in many cases actually hanging over the natural grass areas bounding the runway or taxiway, thus greatly increasing the risk of damage to aircraft engines by the presence of foreign objects.  
           [0003]    The majority of airport runway and taxiway shoulders are constructed of asphalt which may have deteriorated surfaces and edges, such as cracking and spalling. This creates a serious risk of damage to aircraft and particularly aircraft engines overhanging the airstrip shoulders caused by foreign objects such as loose pieces of asphalt and debris that could be ingested by the aircraft engines. Foreign object damage is a primary safety concern for both airport operators and aircraft manufacturers since it could have catastrophic results. In addition to foreign object damage potential, asphalt pavements require periodic maintenance and/or complete replacement which adds to the overall airport operation costs.  
           [0004]    In order to minimize the risk of foreign object damage to aircraft engines and in order to comply with regulatory safety issues, one solution is to increase the width of existing runways and taxiways using concrete or asphalt placed over deep bases in traditional construction methods. However, the costs related to traditional construction methods and to airport operation down-time resulting from the traditional construction are very significant and in some cases not feasible.  
           [0005]    Air fields are generally constructed in large open areas and so in addition to jet blasts and vortex shedding, they are exposed to wind storms, ice and snow storms as well as sand storms, which requires expensive maintenance of existing topsoil bounding the runways and taxiways, such as cutting, grooming, cleaning, etc., in order to ensure efficient surface drainage of water, and to avoid water ponding and possibly freezing of the surface water on the runway.  
           [0006]    Therefore, there is a need for improvement of airport runways and taxiways, particularly the need for improvements of the extension of existing runway and taxiway shoulders.  
         SUMMARY OF THE INVENTION  
         [0007]    An object of the present invention is to provide a method for improving safety of airport runways and taxiways.  
           [0008]    Another object of the present invention is to provide a cost-effective solution for the extension of existing runway and taxiway shoulders at airports in order to minimize the risk of foreign object damage to aircraft engines.  
           [0009]    A further object of the present invention is to provide an airport runway and taxiway shoulder-bordering surface arrangement to extend the width of existing runway and taxiway shoulders, thereby reducing the potential for damage to aircraft engines by foreign objects.  
           [0010]    In accordance with a general aspect of the present invention, there is provided a method for improving safety of airport airstrips comprising steps of:  
           [0011]    a) providing a flexible surfacing material; and  
           [0012]    b) extending the width of an existing shoulder of the airstrip by installing said flexible surfacing material along a side of said airstrip.  
           [0013]    In accordance with a more specific aspect of the present invention, the method comprises the steps of: providing a compacted soil base bounding a shoulder of an airstrip; placing a flexible, water-impermeable surfacing material on the compacted soil base; and anchoring the surfacing material to the airstrip in a water-tight manner so that the surfacing material will assure efficient surface drainage of water and allow for unobstructed run-off of loose particles.  
           [0014]    It is preferable to further lay a synthetic grass surface on an area beyond the surfacing material so that loose particles can be trapped thereby when being driven by jet blasts from the airstrip and running off the surfacing material.  
           [0015]    In accordance with another aspect of the present invention, an airport runway and taxiway shoulder-bordering surface arrangement is provided to extend the width of existing runway and taxiway shoulders, thereby eliminating the potential for damage to aircraft engines by loose particles. The arrangement comprises a compacted soil base bounding an airstrip and a flexible water-impermeable surfacing material placed on the compacted soil base and directly adjacent to a side edge of the airstrip. Means are provided for anchoring the surfacing material to the edge of the airstrip in a water-tight manner so that the surfacing material will assure efficient surface drainage of water and allow for unobstructed run-off of loose particles. It is noted that the flexible water-proof surfacing material can be installed directly on the existing paved airstrip shoulder area in order to reduce the cost of excavating the existing asphalt and to keep the existing shoulder in place.  
           [0016]    In accordance with a further general aspect of the present invention, there is provided an airfield safety arrangement for reducing the risk that an aircraft engine be damaged as a result of the ingestion of foreign objects from an area adjacent an airstrip, the safety arrangement comprising a ground surfacing material adapted to be laid down on the ground so as to extend laterally outwardly from an airstrip, the ground surfacing material having a relatively smooth shedding surface sloping downwardly from the airstrip to provide for surface water drainage and run-off of loose particles to a location wherein the particles are not subject of being ingested by the engines of the aircrafts on the airstrip, and an edge anchoring system for bonding the ground surfacing material in a water-tight manner to the airstrip. The surfacing material may be provided with a textured pattern as long as it does not impede run-off of loose particles.  
           [0017]    Still in accordance with the present invention, there is provided an airstrip shoulder-bordering surface arrangement for extending the width of existing runway and taxiway shoulders in order to reduce the potential for damage to aircraft engines by foreign objects (FOD), the arrangement comprising a flexible water-impermeable surfacing material adapted to extend laterally of a side edge of an airstrip shoulder; and an edge-fastening system for securing the surfacing material in position relative to the airstrip shoulder and prevent water migration therebetween, the surfacing material having a relatively smooth top surface to provide for water surface drainage and unobstructed run-off of loose particles.  
           [0018]    The surfacing material preferably further includes reflective and luminescent materials (for instance phosphorescent materials) to provide perimeter lines and runway identification markings so that in situations where the luminescent effect of the reflective materials has faded the aircraft lights would be reflected. The reflective or luminescent materials can be provided as an integral part of the surfacing material or can be applied thereon such as by bonding, painting or other by using any other appropriate techniques. The surfacing material is preferably in a green colour, or could be other colours if required to make a strong visual contrast between the runway and taxiway edges and the edge of the natural field.  
           [0019]    In another embodiment of the present invention, the arrangement further includes a synthetic grass surface covering an area beyond the surfacing material which is permanently bonded to the surfacing material. Thus, the relatively smooth texture of the surfacing material will allow for unobstructed run-off of any loose particles that might be present on the runway and taxiway shoulders and could present a potential for foreign object damage to aircraft engines. As an added value, the replacement of natural grass surfaces with the surfacing material in combination with the synthetic grass surface can provide considerable cost benefits with regards to airport maintenance budgets. This artificial grass can be either permeable or impermeable depending on the specifications for the specific application.  
           [0020]    Substantial savings in airport maintenance budgets can be achieved with the installation of the surfacing material which is virtually maintenance free. In addition, the installation of the synthetic grass surface would eliminate the need for the trimming and cutting of natural grasses. The artificial grass would retain its permanent green colour and texture throughout the year, thus eliminating the need to re-sod old and dead natural grass. In hot and arid climates, for example, in the Middle East, the relatively smooth shedding surface of the surfacing material would allow the removal of sand and other loose foreign objects quickly and efficiently from the shoulders simply as a result of the wind or air turbulence created by aircrafts or other mechanical means. Regular maintenance to keep the extended shoulders free of hazardous debris can be conducted easily, quickly and economically. The debris is displaced into the adjacent synthetic grass turf where the debris will be trapped. If necessary the accumulated debris can be vacuumed out periodically.  
           [0021]    In cold climates accumulated snow can be easily and quickly removed from the surfacing material either by large blowers or sweepers, to a distance beyond the overhang of aircraft engines.  
           [0022]    Since the surfacing material is completely water-tight, the risk of settlement and deterioration of the supporting base would be eliminated, thus providing a stable base for maintenance vehicle circulation year-round.  
           [0023]    The pattern of installation of the surfacing material with the seams running parallel to the existing shoulder edges would not interfere with maintenance operations.  
           [0024]    Other advantages and features of the present invention will be better understood with reference to preferred embodiments thereof described hereinafter.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which:  
         [0026]    [0026]FIG. 1 is a perspective view of an airport runway having shoulder extensions in accordance with a preferred embodiment of the present invention;  
         [0027]    [0027]FIG. 2 is a cross-sectional view of an airstrip shoulder-bordering arrangement in accordance with a first embodiment of the present invention; and  
         [0028]    [0028]FIG. 3 is a cross-sectional view of an airstrip shoulder-bordering arrangement in accordance with a second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    [0029]FIG. 1 illustrates an airport runway  10  comprising a central take-off/landing strip  11  and a pair of runway shoulders  12 . Each shoulder  12  is extended laterally outwardly by means of a shoulder-bordering arrangement comprising a soft ground cover or flexible water-proof surfacing material  14 .  
         [0030]    As shown in FIG. 2, the installation of the surfacing material  14  normally begins with a first step of removing the existing organic material contained in the uppermost stratum of the ground G bounding the shoulders  12  of the runway or taxiway which is generally referred to as an airstrip throughout this application, to a depth dictated by the soil report. The ground G is excavated down to a compactable earth surface. At that point, the soil is graded and compacted by being rolled and shaped to meet the required slopes such that the flow of surface water will be controlled to drain to specific locations. The rocks are removed from the compacted soil base and if required, a layer of engineered backfill will be installed and compacted prior to installing the surfacing material  14  directly on the compacted backfill if specified to do so. It is noted that in some applications, the surfacing material  14  may be laid down directly on the ground without the need for excavating.  
         [0031]    The flexible surfacing material  14 , which is a plastic composite, for example polypropylene, urethane, vinyl or polyethylene, is laid directly on the compacted soil base adjacent to the edge of the existing airstrip shoulder  12 . As shown in FIG. 3, the surfacing material  14  may also be installed so as to at least partly cover or overlap the shoulder  12  of the airstrip (i.e. the runway or the taxiway). This is particularly applicable in the case where the existing shoulder would have to be repaired or re-paved. The surfacing material  14  has a relatively smooth texture having a thickness of between 50 mm and 400 mm. The surfacing material  14  can be provided in the form of a polyethylene, polypropylene or any other type of plastic or composite material that can be sprayed or laminated upon a mesh substrate. The polyethylene or any equivalent thereof could be sprayed or applied by various methods on site or at the manufacturing plant. The surfacing material  14  is completely water-impermeable and is preferably permanently bonded to an edge-fastening system or anchoring system  16  placed next to the existing airstrip shoulder edges or to the shoulder  12  directly since all installations are different.  
         [0032]    The installation of the surfacing material  14  is completed by overlapping rolls of the surfacing material and applying a heat treatment, such as thermal welding, or by applying adhesives to the overlapping surfacing materials, thus fusing the two materials together to obtain a permanent, water-tight and strong bonding of the seams.  
         [0033]    In the illustrated embodiment, the surfacing material  14  is bonded in a water-tight manner to the airstrip shoulder  12 . More particularly, the interface between the edge of the existing airstrip shoulders and the first roll of the surfacing material can be made water-tight by installing impermeable elastomeric sealers in order to assure a continuous and uninterrupted surface drainage of the impermeable surface. The impermeable elastomeric sealer is incorporated with the specially designed anchoring system  16  which assures the safe, permanent and economical anchoring of the edges of the surfacing material  14  to the immediately adjacent existing airstrip shoulders  12 .  
         [0034]    The anchoring system  16  preferably includes a prefabricated, extruded plastic member  18 , for example polypropylene or other plastic that can be thermally bonded to the flexible surfacing material  14 . The extruded plastic member  18  is partially embedded in specially formulated expanding foam  20  which is injected into a narrow excavated trench along the edge of the airstrip shoulder  12 . The excavation, injection of foam, and bonding of the plastic member  18  are completed simultaneously in one operation. The plastic member  18  has an anchoring portion  24  from which extends a leg  26  supporting an above-ground section or head  22  to which the first row of surfacing material  14  is thermally or mechanically bonded. For instance, bonding of the surfacing material  14  can be done by applying a heat activated treatment or by applying adhesives to the overlapping of the surfacing material  14  and the extruded plastic member  18 , thus permanently fusing the two materials together. This anchoring system  16  provides a water-tight seal between the airstrip shoulder edge and the surfacing material  14 . A sealer  27  is preferably provided along the vertical interface between the shoulder  12  and the ground surfacing arrangement, as shown in FIG. 2.  
         [0035]    When the entire surfacing material  14  is in place, the surfacing material  14  will take the shape and the slope of the underlying compacted soil base and will stay flat to provide the relatively smooth shedding surface to provide for water drainage and run off of loose particles. The extent in width and length to which the surfacing material  14  is installed will depend on the performance and design criteria of the specific sites. The areas beyond the surfacing material  14  could be covered with artificial grass  30  which would trap any born particles, such as sand displace by aircraft. The synthetic grass surface is permanently bonded to the surfacing material  14  such as by applying the thermal welding technique or by applying adhesives to assure a permanent water-tight seam between the surfacing material  14  and the synthetic grass surface  30 .  
         [0036]    The synthetic grass surface  30  generally includes a pile fabric  32  which is preferably placed over a compacted soil base substantially free of organic matter. The pile fabric  32  includes a plurality of pile elements  34  resembling blades of grass and extending from a relatively thin and flexible backing mat  36  to a predetermined height thereabove. A non-water retaining ballast material  38  for stabilizing the pile fabric  32  in place is provided on the backing mat  36  and has a thickness less than the predetermined height of the pile elements  34 . The ballast material  38  is provided in the form of a relatively thick layer of particulate material dispersed among the pile elements  34  on the backing mat  36 . The synthetic grass is typically installed on a sloped base for directing water from the pile fabric  32  to the designed storm water management system. Surface drainage is important since it is easier to prepare and can work at lower cost.  
         [0037]    The rows of pile elements  34  can be similar to that described in Applicant&#39;s co-pending Canadian Patent 2,218,314 filed on Oct. 16, 1997, and laid open on Sep. 10, 1998, the contents of which are incorporated herein by reference.  
         [0038]    A thin impermeable membrane  40  is laid on the compacted soil base to prevent water from percolating down thereto. A drainage enabling layer  42  which comprises a thick layer of aggregate, such as rock particulates, is provided on the impermeable membrane  40 . The flexible baking mat  36  is placed on the drainage enabling layer  42  so that the water can readily flow from the backing mat  36  through the drainage enabling layer  42  onto the impermeable membrane  40  and into storm sewers placed at strategic locations. This embodiment is described with more details in Applicant&#39;s PCT application PCT/CA01/01275, entitled ARTIFICIAL GRASS FOR LANDSCAPING, filed Sep. 5, 2001, the specifications of which is incorporated herein by reference. It is noted that the water barrier could be integrated to the backing mat  36  in which case the infill layer  38  would act as the drainage enabling layer.  
         [0039]    As shown in FIG. 2, the surfacing material  14  can be bonded to the edge of the impermeable membrane  40  to provide a water-tight seal between the synthetic grass surface  30  and the surfacing material  14 . Alternatively, the surfacing material could be placed underneath the backing mat  36  and be thermally or adhesively bonded thereto.  
         [0040]    As an added safety feature, the surfacing material  14  can be fabricated with a permanent colour such as green, or with other colours if required to enhance visual contrast between the central landing zone of the airstrip  10  and the shoulders  12  thereof. The surfacing material  14  can also be designed to accept solar energy absorbing fabrics which will dissipate a luminescent glow during the night without the need of outside power sources. The luminescent reflective glow would last up to 10-12 hours to cover the dusk to dawn period. The solar absorbing fabric can be coated directly onto the installed surfacing material  14  or can be installed during fabrication. Patterns spacing and shape factors can be custom fabricated to meet specific airport operation specifications. The solar absorbing fabric can advantageously replace conventional lighting systems for small airports.  
         [0041]    The surfacing material  14  can further include special reflective fabrics installed thereon to enhance the visibility of the runway path for aircraft landing during the night. Thus in situations where the luminescent effect of the solar absorbing fabric fades, the aircraft lights will be reflected by the one-way reflective fabrics to facilitate safe landing.  
         [0042]    As shown in FIG. 3, the surfacing material  14  can be installed directly on an existing shoulder  12  and anchored thereto by means of an anchor member  18 ′ provided in the form of a plastic extrusion placed in a trench formed in the shoulder  12  and fixed in position therein by means of a plurality of anchoring bars. The surfacing material  14  can be thermally or adhesively bonded to the anchor member  18 ′ or even mechanically attached thereto, as described hereinbefore with respect to FIG. 2. Alternatively, the surfacing material  14  could be adhesively bonded directly to the shoulder  12 . A given thickness of material is removed from the shoulders  12  so that the surfacing material  14  is substantially flush with the take-off/landing strip  11 .  
         [0043]    Protection against foreign object damage (FOD) can be further enhanced by incorporating a guidance system into the surfacing material for guiding a robot  48  parallel the runway  10  in order to locate and detect FOD materials that could be ingested by the aircraft engines. The guidance system could include a magnetic guidance wire  46  embedded in the surfacing material  14  or any other type of guidance technology.  
         [0044]    By having guidance wires embedded into the flexible surfacing material  14 , drainage of the runway would not be impeded by channels or protruding edges to guide the robots  48 . The robots  48  could also be designed to clear the flexible fabric of sand and FOD by means of having a larger robot made with the necessary blowers to do so. The FOD detecting robot would need to be heavy and stable enough to not be displaced from the wind and or jet wash. A cable system could also be used to guide the robot along and keep the robot tethered.  
         [0045]    Modifications and improvements to the above-described embodiment of the present invention may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.