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Suggested Citation:"Chapter One - Introduction." National Academies of Sciences, Engineering, and Medicine. 2008. Impact of Airport Pavement Deicing Products on Aircraft and Airfield Infrastructure. Washington, DC: The National Academies Press. doi: 10.17226/13913.
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Suggested Citation:"Chapter One - Introduction." National Academies of Sciences, Engineering, and Medicine. 2008. Impact of Airport Pavement Deicing Products on Aircraft and Airfield Infrastructure. Washington, DC: The National Academies Press. doi: 10.17226/13913.
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Page 4
Page 5
Suggested Citation:"Chapter One - Introduction." National Academies of Sciences, Engineering, and Medicine. 2008. Impact of Airport Pavement Deicing Products on Aircraft and Airfield Infrastructure. Washington, DC: The National Academies Press. doi: 10.17226/13913.
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Page 5

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

3This report provides the synthesis of results from ACRP Proj- ect S10-03. This introductory chapter, describing the purpose and background of the report, provides the context for the remaining chapters. PURPOSE OF SYNTHESIS This synthesis reports on how airports chemically treat their airfield pavements to mitigate snow and ice, and the chemi- cals used; reviews damage to aircraft components and air- field infrastructure in association with the use of traditional or modern pavement deicing products (PDPs) (for simplic- ity, this document uses the terms “deicer” and “pavement deicing products” for all chemical products used for deicing and anti-icing operations); and identifies critical knowledge gaps on these subjects. Field reports of the aviation industry increasingly suggest that the use of PDPs, including alkali acetate and alkali formate products (such as sodium- and potassium-acetate-, and formate-based products), on aprons, runways, and taxiways may result in damage to various air- craft and airfield infrastructure under certain conditions. BACKGROUND Airfield pavement deicing and anti-icing are essential activi- ties in maintaining the aviation industry’s safe winter opera- tions. The general preference for aviation’s winter maintenance practices is anti-icing with approved chemicals to prevent the bonding of ice and pavement—a more proactive approach than deicing or sanding. For anti-icing, liquid chemicals are preferred for their better dispersion and adherence, because solid chemicals can be easily scattered by wind, aircraft, and ground support vehicles. For deicing, chemicals are applied to melt ice and disrupt any bond to the pavement, whereas sand can increase the frictional characteristics of the surface (“Air- port Winter Safety and Operations” n.d.). Mechanical methods can reduce the amount of deicing chemicals applied; however, care must be taken to avoid polishing ice and creating a haz- ard that is more difficult to treat (Pro-Act Fact Sheet . . . 1998). The traditional airfield PDPs consisting of urea or glycols have become less popular owing to their adverse environmen- tal impacts. New PDPs have emerged as alternatives that often contain potassium acetate (KAc), sodium acetate (NaAc), sodium formate (NaF), or potassium formate (KF) as the freez- ing point depressant. KAc, NaAc, and NaF are more expen- sive, but also more effective than urea at lower temperatures (−20°F, 10°F, and 5°F, respectively) (Pro-Act Fact Sheet . . . 1998). In Canada, the general consensus was that the increased effectiveness and simultaneous reduction in environmental problems justifies the increased cost of using new PDPs (Com- fort 2000). Airports and airlines deal with multiple objectives and are challenged with multiple constraints when it comes to airfield pavement deicing and anti-icing. First, aircraft safety (and mobility) is of the highest priority, which at times demands large quantities of PDPs to be used for snow and ice control on airfield pavements. Because passenger and flight crew safety is of paramount importance, the aviation regulators and airframe and aircraft component manufacturers strive to ensure the highest standards possible. For instance, critical control systems for aircraft are designed with an “extremely remote” probability of failing, which is one-in-one-billion (10−9) flights (National Academy of Engineering 1980). Air- craft safety is also ensured by mandating regular regimes of inspection, maintenance, and replacement of aircraft brakes and components to manage the highly improbable but poten- tially catastrophic risks. Second, environmental regulatory compliance is an impor- tant objective as a result of requirements of the Clear Water Act and National Pollution Discharge Elimination System permits for stormwater discharges. Officials at more than half of the airports that responded to a 2000 U.S. General Accounting Office survey indicated that it was getting much more difficult to balance environmental concerns with their airport’s operations (General Accounting Office 2000). The EPA is in the process of developing effluent limitation guide- lines for airport deicing and anti-icing operations that may pose additional challenges for airports and airlines in achiev- ing environmental compliance. The use of liquid glycol-based and solid urea deicers has received particular scrutiny owing to the high biochemical oxygen demand [BOD, often mea- sured as 5-day BOD (BOD5 in mg/L)] exerted on receiving bodies of water. Depleted oxygen levels can threaten aquatic life, whereas the ammonia by-product of urea is toxic to aquatic organisms (Pro-Act Fact Sheet . . . 1998). Although glycol-based deicers are increasingly less commonly used for pavement deicing, urea was still used by more than one-third of the 50 busiest airports in 2000 (General Accounting Office 2000) and more than one-third of the airports that reported using chemical deicers by a more comprehensive CHAPTER ONE INTRODUCTION

4EPA survey in 2006. The reduced oxygen demand by acetate- and formate-based deicers compared with urea is evident in Table 1, as reported as chemical oxygen demand. Testing for chemical oxygen demand is faster than standard BOD tests and indicates the theoretical maximum oxygen that would be consumed; BOD is related more to biological decomposition. Third, materials compatibility between PDPs and the air- craft and airfield infrastructure is yet another objective. Field reports suggest that the use of modern PDPs, including alkali acetate and alkali formate products on aprons, runways, and taxiways may result in the need for more frequent mainte- nance and inspection for various aircraft and airfield infra- structure. Such PDPs have recently been reported to corrode or degrade cadmium or aluminum components and carbon– carbon (C/C) composite brakes of aircraft. Often mixed with corrosion inhibitors, KAc and KF were reported to degrade insulation in aircraft electrical systems. Existing research has indicated that KAc and KF may cause accelerated structural degradation of C/C composite aircraft brakes as a result of the catalytic oxidation by the potassium cation, which may result in reduced brake life and introduce the possibility of brake failure during aborted take-off. KF was found to cause corrosion to landing gear and associated wiring of some Boeing airplane models. Other examples of damage poten- tially associated with the use of PDPs include reports of cor- rosion in landing gear joints, electrical wire bundle degrada- tion, corrosion of runway lighting fixtures, and damage to airfield pavements. Airfield pavement damage has been ob- served in both asphalt and concrete runways. Evidence of the former is more widely reported in European airports; how- ever, laboratory tests worldwide have shown emulsification of asphalt and the disruption of asphalt-aggregate bonds. Exten- sive laboratory testing of concrete pavement has shown an increase in alkali–silica reactivity and the need for improved standardized tests for aggregate selection and mix design. Finally, operational implementation viability is another con- straint for airports and airlines to consider. The FAA prescribes a list of chemicals that are approved for the snow and ice con- trol of airfield pavements, which limits options of chemicals being used as PDPs. The approval of PDPs by the FAA advi- sory circular (“Airport Winter Safety and Operations” n.d.) is currently based on two specifications of the SAE through Aero- space Material Specifications (AMS). Approved glycol- and potassium-acetate-based fluids must meet SAE AMS 1435B, Fluid, Generic Deicing/Anti-icing, Runways and Taxiways. Approved airside urea, calcium magnesium acetate, sodium formate, and sodium acetate products must meet SAE AMS 1431C, Compound, Solid Runway and Taxiway Deicing/ Anti-icing. Airside urea must also meet the military specifica- tion MIL SPEC DOD-U-10866D, Urea-Technical (“Airport Winter Safety and Operations” n.d.). In addition, more costly PDPs must be justified and programmed into operating bud- gets. The costs associated with both aircraft and airfield main- tenance and alleviating the environmental impacts of PDPs must be balanced in decision making for deicing and anti-icing operations. Alternative PDPs may also pose new challenges related to rules of practice and training. The previously mentioned multiple dimensions of this complex problem define the context of this synthesis. There are no simple solutions to the competing, and sometimes conflicting, objectives of aircraft safety, environmental reg- ulatory compliance, materials compatibility, and operational implementation viability. ACRP has two airfield deicing research projects underway at this time: ACRP Project 02-01, Alternative Aircraft and Airfield Deicing and Anti-Icing Formulations with Reduced Aquatic Toxicity and Biochemical Oxygen Demand, which responds to the voiced need for new formulations of aircraft and airfield deicers that combine safety, performance, and materials compatibility with environmental stewardship and cost-effectiveness. The identification of new formulations will be based primarily on reduced toxicity and BOD5 and evalu- ated based on their performance, efficiency, material compat- ibility, and environmental, operational, and safety impacts. Airports of all sizes and operational levels are reporting in- creased difficulty in balancing environmental concerns dur- ing their operations (General Accounting Office 2000). ACRP Project 02-02, Managing Runoff from Aircraft and Airfield Deicing and Anti-Icing Operations, will provide an array of planning guidelines with best management practices useful for the implementation of site-specific solutions for the col- lection of deicer runoff while still maintaining safe aviation. These guidelines can provide sound technical information in support of the ongoing effort by the EPA to establish effluent guidelines for discharges of deicing runoff. To avoid duplication, this synthesis strictly limits this report to how airports chemically treat their airfield pave- ments to mitigate snow and ice, and chemicals used; reviews damage reported to aircraft components and airfield infra- structure in association with the use of traditional or modern PDPs; and identifies critical knowledge gaps on these sub- jects. Such information is expected to provide a holistic view of airfield pavement deicing and anti-icing operations and assist in the design of new deicer formulations. METHODOLOGY This synthesis was primarily based on a critical review of lit- erature and a formal survey with follow-up interviews. TABLE 1 CHEMICAL OXYGEN DEMAND FOR RUNWAY DEICERS Potassium Formate Potassium Acetate Urea COD [g(O2)/kg dry deicer] 190 653 2,133 COD (kg/10 hectare surface) 285 1,134 5,365 Adapted from Sava (2007). Deicers

5Literature Review Information was assembled through a comprehensive search of literature and data sources to review damage reported to air- craft components and airfield infrastructure in association with the use of traditional or modern PDPs and to identify critical knowledge gaps on this topic. The search was carried out using a variety of tools, including TRIS online, Google Scholar, SCIFinder Scholar, Google, etc. Relatively limited informa- tion in academic peer-reviewed literature was found and thus industry peer-reviewed publications and reports published by the FAA, aircraft brake manufacturers, airframe manufactur- ers, airlines, airports, and PDP manufacturers were incorpo- rated in the review process with caution. Information sources included, but were not limited to: • U.S. General Accounting Office—results from a survey of the nation’s 50 busiest commercial service airports. • SAE Working Groups (A-5A Brake Manufacturers, G-12F Catalytic Oxidation, G-12F Cadmium Corro- sion, and G-12F Fluid Residues). • SAE specification documents AMS 1431 and AMS 1435. • JÄPÄ—Finnish De-icing Project reports. • Innovative Pavement Research Foundation (IPRF). • Industry groups such as the ACI–NA, AAAE, NASAO, and ATA. • Government groups such as the FAA, Transport Canada, and U.S. Air Force. • Airlines [Alaska Airlines, American Airlines, ANA, British Airways, Continental Airlines, FlyBe, KLM, Northwest Airlines, SRTechnics (formerly Swissair), Stockholm–Arlanda, and United Airlines]. • Airframe and component manufacturers (Airbus, Boeing, Bombardier, Honeywell, Goodrich, and Messier– Bugatti). • PDP manufacturers (ADDCON Nordic, Clariant, Cryo- tech Deicing Technology, Dow Canada, Kilfrost, and Old World Industries). Survey With the support of the ACRP project manager and technical panel members, a portion of the responses to the 2006 EPA Airport Deicing Questionnaire were received, including the type of PDPs used by approximately 100 airports (including urea, KAc, NaAc, NaF, ethylene glycol-based fluids, propy- lene glycol-based fluids, and others), and contact information from the 50 busiest U.S. airports that reported using PDPs as well as several foreign airports including CPH (Copenhagen, Denmark), LGW (London–Gatwick, United Kingdom), and OSL (Oslo, Norway). The EPA questionnaire did not provide information specif- ically related to the effects of PDPs on aircraft and airfield infrastructure. Thus, a survey was created under the guidance and review of the technical panel members to solicit input from many stakeholder groups: airframe and aircraft com- ponent manufacturers, airport infrastructure management, air carriers, military aviation, and industry and government groups. Early in the survey (see Appendix A), respondents were directed to any of four sections based on their role in the field of aviation: aircraft component manufacturing, air- port management, PDP manufacturing, or air carriers. There were 43 responses to the ACRP survey. The distribution of responses based on perspective is shown in Figure 1, with more detailed information of survey respondents available in Appendix B. ORGANIZATION OF SYNTHESIS The following chapter will describe the use of PDPs at air- ports based on results from the 2006 EPA questionnaire and the ACRP survey distributed for this synthesis. Chapter three offers detailed information about the effects of PDPs on air- craft, including catalytic oxidation of C/C composite brakes, cadmium corrosion, and interaction with aircraft deicing and anti-icing fluids. Chapter four presents the currently avail- able information on the effects of PDPs on asphalt and con- crete airfield pavements, as well as the limited information available on other airfield infrastructure. These chapters describe the problems attributed to PDPs with possible sci- entific mechanisms of damage, as well as mitigation mea- sures and knowledge gaps. Finally, chapter five summarizes the findings related to the effects of PDPs on aircraft and air- field infrastructure. FIGURE 1 Classification of survey respondents. Military Aviation 2% Other 7% PDP Manufacturers 5% Airport Management 35% Industry or Government Groups 7% Air Carriers/Airlines 21% Airframe and Aircraft Component Manufacturing 23%

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TRB’s Airport Cooperative Research Program (ACRP) Synthesis 6: Impact of Airport Pavement Deicing Products on Aircraft and Airfield Infrastructure explores how airports chemically treat their airport pavements to mitigate snow and ice, and the chemicals used. The report also examines the effects of pavement deicing products on aircraft and airfield infrastructure, and highlights knowledge gaps in the subject.

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