SLIDEREAD

9/30 AC 150/5320-6ECHAPTER 3. PAVEMENT DESIGN FOR AIRPLANES WEIGHINGMORE THAN 30,000 POUNDSSECTION 1. DESIGN CONSIDERATIONS.300.SCOPE. This chapter provides pavement design guidance for airfield pavements intended to serve airplaneswith gross weights in excess of 30,000 pounds (13 608 kg). Chapter 5 discusses the design of pavements serving lighterairplanes with gross weights under 30,000 pounds (13 608 kg).301.DESIGN PHILOSOPHY. The foreword of this AC describes the FAA policy of treating the design ofairplane landing gear and the design and evaluation of airport pavements as three separate entities. The design of airportpavements is a complex engineering problem that involves a large number of interacting variables. This chapter presentspavement mechanistic design procedures that are implemented in the FAA Rigid and Flexible Iterative Elastic LayerDesign (FAARFIELD) program. FAARFIELD implements both layered elastic-based and three-dimensional finiteelement-based design procedures for new and overlay designs of flexible and rigid pavements, respectively.Because of thickness variations, the evaluation of existing pavements should be performed using the same methodemployed for design. Chapter 6 describes in detail procedures to use when evaluating pavements. Details on thedevelopment of the FAA method of design are as follows:a.Flexible Pavements. For flexible pavement design, FAARFIELD uses the maximum vertical strain atthe top of the subgrade and the maximum horizontal strain at the bottom of the asphalt surface layer as the predictors ofpavement structural life. FAARFIELD provides the required thickness for all individual layers of flexible pavement(surface, base, and subbase) needed to support a given airplane traffic mix over a particular subgrade.b.Rigid Pavements. For rigid pavement design, FAARFIELD uses the maximum horizontal stress atthe bottom edge of the PCC slab as the predictor of pavement structural life. The maximum horizontal stress for designis determined using an edge loading condition. FAARFIELD provides the required thickness of the rigid pavement slabneeded to support a given airplane traffic mix over a particular subgrade/subbase.302.REPORTING PAVEMENT STRENGTH.When designing new pavements, summarize all pavementdesigns on FAA Form 5100-1, Airport Pavement Design, which is considered part of the Engineer’s Design Report.Submit the Engineer’s Design Report for FAA review and approval along with initial plans and specifications.303.BACKGROUND. An airfield pavement and the airplanes that operate on it represent an interactive systemthat must be addressed in the pavement design process. Design considerations associated with both the airplanes and thepavement must be recognized in order to produce a satisfactory design. Producing a pavement that will achieve theintended design life will require careful construction control and some degree of maintenance. Pavements are designedto provide a finite life and fatigue limits are anticipated. Poor construction and a lack of preventative maintenance willshorten the service life of even the best-designed pavement.a.Variables. The determination of pavement thickness requirements is a complex engineering problem.Pavements are subject to a wide variety of loading and climatic effects. The design process involves a large number ofinteracting variables, which are often difficult to quantify. Despite considerable research on this subject, it has beenimpossible to arrive at a direct solution for thickness requirements. For this reason, pavement engineers must basepavement thickness on a theoretical analysis of load distribution through pavements and soils, the analysis ofexperimental pavement data, and a study of the performance of pavements under actual service conditions. The FAAdeveloped the FAARFIELD program using failure models based on full-scale tests conducted from the 1940s until thepresent. Pavements designed and constructed in accordance with FAA standards are intended to provide a minimumstructural life of 20 years that is free of major maintenance if no major changes in forecast traffic are encountered.Rehabilitation of surface grades and renewal of skid-resistant properties may be needed before 20 years because ofdestructive climatic effects and the deteriorating effects of normal usage.b.Structural Design. The structural design of airport pavements consists of determining both theoverall pavement thickness and the thickness of the component parts of the pavement. There are a number of factorsthat influence the thickness of pavement required to provide satisfactory service. These include the magnitude andcharacter of the airplane loads to be supported, the volume of traffic, the concentration of traffic in certain areas, and thestrength of the subgrade soil and quality of materials that make up the pavement structure.13

AC 150/5320-6E304.9/30 PAVEMENT DESIGN USING FAARFIELD.a.Purpose. The design procedure presented in this chapter provides a method of design based onlayered elastic and three-dimensional finite element-based structural analysis developed to calculate design thicknessesfor airfield pavements. Layered elastic and three-dimensional finite element-based design theories were adopted toaddress the impact of new complex gear and wheel arrangements. The design method is computationally intense, so theFAA developed a computer program called FAARFIELD to help pavement engineers implement it.b.Application. The procedures and design software identified in this chapter are intended to providepavement thickness design standards for all airfield pavements. To aid in the design review, the summary informationfrom the design software should be printed and included with the pavement design submittal. The summaryinformation can be printed from the FAARFIELD Notes Window by clicking the ‘Save XML’ button. FAARFIELDthen saves the information into an Extensible Markup Language (XML) format file for future import into FAA Form5100-1.FAARFIELD is based on the cumulative damage factor (CDF) concept, in which the contribution of each airplane in agiven traffic mix to total damage is separately analyzed. Therefore, the FAARFIELD program should not be used tocompare individual airplane pavement thickness requirements with the design methods contained in previousversions of the AC that are based on the “design aircraft” concept. Likewise, due care should be used when usingFAARFIELD to evaluate pavement structures originally designed with the thickness design curves in previousversions of this AC. Any comparison between FAARFIELD and the design curve methodology from previousversions of this AC must be performed using the entire traffic mix.c.Computer Program. The structural computations are performed by two subprograms withinFAARFIELD. These subprograms are called LEAF and NIKE3D FAA. LEAF is a layered elastic computationalprogram implemented as a Microsoft WindowsTM dynamic link library written in Visual BasicTM. NIKE3D FAAis a three-dimensional finite element computational program implemented as a dynamic link library written inFORTRAN. NIKE3D FAA is a modification of the NIKE3D program originally developed by the Lawrence LivermoreNational Laboratory (LLNL) of the U.S. Department of Energy and is distributed in compiled form under a softwaresharing agreement between LLNL and the FAA.(1)Airplane Considerations. A wide variety of airplanes with pertinent pavement designcharacteristics are stored in the program library. The FAARFIELD internal airplane library is divided into six airplanegroups: Generic, Airbus, Boeing, Other Commercial, General Aviation, and Military. The designer has considerablelatitude in selecting and adjusting airplane weights and frequencies.(i)Load. The pavement design method is based on the gross weight of the airplane.The pavement should be designed for the maximum anticipated takeoff weight of the airplane at the anticipated facility.The design procedure assumes 95 percent of the gross weight is carried by the main landing gears and 5 percent iscarried by the nose gear. FAARFIELD provides manufacturer-recommended gross operating weights for many civil andmilitary airplanes. The FAA recommends using the maximum anticipated takeoff weight, which provides some degreeof conservatism in the design. This will allow for changes in operational use and forecast traffic. The conservatism isoffset somewhat by ignoring arriving traffic.(ii)Landing Gear Type and Geometry. Gear type and configuration dictate howairplane weight is distributed to a pavement and how the pavement will respond to airplane loadings. Table 3-1 showstypical gear configurations and new gear designations in accordance with FAA Order 5300.7, Standard NamingConvention for Aircraft Landing Gear Configurations (Appendix 2).(iii)Tire Pressure. Tire pressure varies depending on gear configuration, gross weight,and tire size. Tire pressure has significantly more influence on strains in the asphalt surface layer than at the subgrade.Tire pressures in excess of 221 psi (1.5 MPa) may be safely exceeded if the pavement surface course and base coursemeet the minimum design requirements for pavement loading along with a high stability asphalt surface.(iv)Traffic Volume. Forecasts of annual departures by airplane type are needed forpavement design. Information on airplane operations is available from Airport Master Plans, Terminal Area Forecasts,the National Plan of Integrated Airport Systems, Airport Activity Statistics, and FAA Air Traffic Activity Reports.Pavement engineers should consult these publications when developing forecasts of annual departures by airplane type.14

9/30 AC 150/5320-6ETABLE 3-1. STANDARD NAMING CONVENTION FOR COMMON AIRPLANE GEARCONFIGURATIONSGear DesignationGear DesignationAirplane ExampleSngl Whl-45SSingleB737-100DDual2SC-1302 Singles in Tandem2DB767- Duals in Tandem3DB777- Duals in TandemC-17A2TTwo Triple Wheels in Tandem15

AC 150/5320-6E9/30 TABLE 3-1. STANDARD NAMING CONVENTION FOR COMMON AIRPLANE GEARCONFIGURATIONS (CONTINUED)Gear DesignationGear DesignationAirplane ExampleDC10-30/402D/D1Two Dual Wheels in Tandem Main Gear/DualWheel Body GearA340-600 std2D/2D12D/2D1 Two Dual Wheels in Tandem MainGear/Two Dual Wheels in Tandem Body Gear2D/2D2B747-400Two Dual Wheels in Tandem Main Gear/TwoDual Wheels in Tandem Body GearA380-8002D/3D2Two Dual Wheels in Tandem Main Gear/ThreeDual Wheels in Tandem Body Gear5DAn-124Five Dual Wheels in Tandem Main Gear16

9/30 AC 150/5320-6E(2)Units. The program may be operated with U.S. customary or metric dimensions.(3)Availability. FAARFIELD can be downloaded from the Office of Airport Safety andStandards website.(4)Related Reference Material. The internal help file for FAARFIELD contains a user’smanual, which provides detailed information on proper execution of the program. The manual also contains additionaltechnical references for specific details of the FAARFIELD design procedure.(5)Airplane Traffic Mixture. FAARFIELD was developed and calibrated specifically toproduce pavement thickness designs consistent with previous methods based on a mixture of different airplanes ratherthan an individual airplane. If a single airplane is used for design, a warning will appear in the Airplane Windowindicating a non-standard airplane list is used in the design. This warning is intended to alert the user that the programwas intended for use with a mixture of different airplane types. Nearly any traffic mix can be developed from theairplanes in the program library. Solution times are a function of the number of airplanes in the mix. The FAARFIELDdesign procedure deals with mixed traffic differently than did previous design methods. Determination of a designaircraft is not required to operate FAARFIELD. Instead, the program calculates the damaging effects of each airplane inthe traffic mix. The damaging effects of all airplanes are summed in accordance with Miner’s law. When the cumulativedamage factor (CDF) sums to a value of 1.0, the design conditions have been satisfied.d.Pavement Design Considerations. There are distinct differences between the previous FAA designmethodology and the methodology contained in FAARFIELD. These differences, along with some common designassumptions between the two methods, are discussed below.(1)Design Life. The FAA design standard for pavements is based on a 20-year design life. Thecomputer program is capable of considering other design life time frames, but the use of a design life other than 20years constitutes a deviation from FAA standards.(2)Traffic Mix. The design procedures in previous versions of this AC required the trafficmixture to be converted into a single design aircraft and all annual departures converted to equivalent annual departuresof the design aircraft. The design aircraft was determined by selecting the most damaging airplane based on theanticipated gross weight and the number of departures for each airplane. As noted in 303c(5), the FAARFIELD designprogram does not convert the traffic mixture to equivalent departures of a design aircraft. Instead, it analyzes thedamage to the pavement for each airplane and determines a final thickness for the total cumulative damage.FAARFIELD considers the placement of each airplane’s main gear in relationship to the pavement centerline. It alsoallows the pavement damage associated with a particular airplane to be completely isolated from one or more of theother airplanes in the traffic mixture.(3)Pass-to-Coverage Ratio. As an airplane moves along a pavement section it seldom travels ina perfectly straight path or along the exact same path as before. This lateral movement is known as airplane wander andis modeled by a statistically normal distribution. As an airplane moves along a taxiway or runway, it may take severaltrips or passes along the pavement for a specific point on the pave