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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2019. Airport Surface Weather Observation Options for General Aviation Airports. Washington, DC: The National Academies Press. doi: 10.17226/25670.
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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.

4 General aviation (GA) aircraft make up the largest category of aircraft operating in the United States. According to the FAA Aerospace Forecast for Fiscal Years 2018–2038, GA operations accounted for 50.8% of all operations handled by the FAA in 2017, with GA hours flown forecast to increase by 0.8% through 2038. The National Plan of Integrated Airport Systems (NPIAS) 2019–2023 indicates that there are a total of 19,627 landing facilities in the United States, that 5,099 of those landing facilities are open for public use, and that 3,321 of those landing facilities are considered NPIAS facilities. Furthermore, 89% of NPIAS airports are classified as nonpri- mary and serve mostly general aviation. The general aviation fleet comprises approximately 213,000 aircraft, while the commercial fleet totals approximately 18,200 aircraft. This means that the majority of both aircraft operations and aircraft landing surfaces in the country are exclusively general aviation–related. These nearly 20,000 landing surfaces are found in every geographic and climatic situation in the country, and general aviation aircraft operate from airports at the highest and lowest eleva- tions (respectively, Lake County Airport in Leadville, CO, at 9,934 mean sea level [MSL] and Furnace Creek Airport in Death Valley at –210 MSL). They operate from the frozen reaches of Alaska to the hottest place in the world (also Death Valley, according to the Guinness Book of World Records [2019]). General aviation aircraft also operate from rivers and lakes, glaciers, grass and gravel airstrips, short runways, and one-way runways, comprising a huge variety of locations not served by commercial service aircraft. General aviation aircraft are thus exposed to all weather phenomena that occur in the country, but the aircraft are typically smaller and less capable of handling extreme weather conditions than the predominately larger and better-equipped aircraft in the commercial fleet. Conse- quently, knowledge of real-time weather conditions across a large geographic area is a critical component for the safety of flight for GA aircraft. In the United States, weather services for aviation uses are offered through a joint effort of the National Weather Service (NWS), the FAA, the Department of Defense (DOD), and private- sector aviation weather providers. The NWS is the largest provider of weather information in the United States. According to the NWS website (https://www.weather.gov/about/forecastsandservice), The National Weather Service (NWS) provides weather, water, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and prop- erty and the enhancement of the national economy. These services include Forecasts and Observations, Warnings, Impact-based Decision Support Services, and Education in an effort to build a Weather-Ready Nation. The website notes that the NWS collects nearly 76 billion observations and provides 1.5 mil- lion forecasts each year: C H A P T E R 1 Introduction

Introduction 5 NWS forecasts, warnings, and data and products form a national information database and infrastruc- ture used by other governmental agencies, the private sector, the public, and the global community. This enables our core partners to make decisions when weather, water or climate has a direct impact on the protection of lives and livelihoods. NWS forecasts and warnings are provided directly to decision makers in local communities, as well as at state and Federal levels, to protect lives and property in your neighbor- hood and community. NWS products utilize observations from a wide variety of sources that include satellites, ground-based radar, and river- and waterway-based sensors, as well as human and automated observations. However, given the large amount of data it collects, it is important that the NWS be able to identify data that is approved for aviation use by the FAA. The interface between the NWS and the National Airspace System (NAS) is the Weather Message Switching Center Replacement (WMSCR). The WMSCR, which is physically located in two facilities in Atlanta and Salt Lake City, collects, processes, and disseminates aviation weather products and information to the NAS. The “customers” of the WMSCR include thousands of organizations, both public and private. Information that is reported to the WMSCR is highly regulated by the various agencies authorized to access it. One of those agencies is the FAA, which facilitates the access of approved aviation weather reporting equipment to the WMSCR through the National Airspace Data Interchange Network (NADIN). Figure 1 illustrates the pathways through which weather reporting equipment accesses the NADIN. The FAA develops and enforces technical specifications for equipment that reports to the WMSCR and then onward to the broader NAS. This equipment includes surface weather obser- vation systems, which provide real-time reporting of weather conditions at thousands of air- ports, and some nonairport locations, across the country. FAA-approved aviation data for surface observation systems conforms to the data format prescribed in Annex 3 to the Convention on International Civil Aviation—Meteorological Service for International Air Navigation (ICAO 2010). This format is the Meteorological Terminal Aviation Routine Weather Report, or METAR. The METAR is a coded data message that reports weather information in a standard format. Elements of the weather report are coded by a variable or series of variables, and pilots are trained to decipher a written METAR. The verbal playback of an Automated Surface Observ- ing System (ASOS) or Automated Weather Observing System (AWOS) follows the order of the METAR. An example of a METAR is given in Figure 2. Because weather can have such a high impact on aviation safety, general aviation pilots are particularly concerned with weather conditions at both their origin and destination airports as well as along their route. The FAA contracts for and supports the dissemination of free weather information for use by pilots through the Leidos (formerly Lockheed Martin) Flight Service Station (FSS) network. Leidos provides flight briefing services and weather interpretation through interaction with a human briefer by calling 1-800-WXBRIEF and via automated services by accessing the website at www.1800wxbrief.com. The federal government also provides free real- time and forecasted weather through the support of the National Oceanic and Atmospheric Administration (NOAA) and the NWS at www.aviationweather.gov. Both Leidos and NOAA provide weather information from FAA-approved reporting sources. Beyond simply safe flying, however, there is a regulatory requirement for GA pilots to be aware of weather conditions along their proposed route of flight. This guidance is found in Title 14 of the Code of Federal Regulations (14 CFR) Part 91.103, which states: Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include— (a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;

6 Airport Surface Weather Observation Options for General Aviation Airports (b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information: 1. For civil aircraft for which an approved Airplane or Rotorcraft Flight Manual containing takeoff and landing distance data is required, the takeoff and landing distance data contained therein; and 2. For civil aircraft other than those specified in paragraph (b)(1) of this section, other reliable information appropriate to the aircraft, relating to aircraft performance under expected values of airport elevation and runway slope, aircraft gross weight, and wind and temperature. The implication of this section is that for all instrument flight rules (IFR) flights and all visual flight rules (VFR) flights that leave the immediate airport environment, the GA pilot must per- form some sort of weather investigation, usually referred to as a weather briefing. The free ser- vices provided by the FAA and NWS can fulfill these requirements for a legal weather briefing. Conducting a flight under IFR rules means the aircraft is under positive control from air traf- fic control (ATC) at all times. Pilots take direction from ATC personnel with regard to heading, altitude, and sometimes airspeed. Virtually all commercial flights, and most general aviation Note: AWSS = Automated Weather Sensor System; ASOS = Automated Surface Observing System; AWOS = Automated Weather Observing System; NOAA = National Oceanic and Atmospheric Administration. Figure 1. NADIN WMSCR pathways.

Introduction 7 Part 135, Part 91K, and turbine aircraft flights, are conducted under IFR rules for most, if not all, of the flight. IFR flight entails a multitude of aircraft requirements and pilot qualifications. IFR flights also require that a flight plan be filed with the FAA documenting all aspects of the proposed flight, from takeoff to landing. Flights conducted under visual flight rules are the most basic type of flying. The pilots are operating at their own discretion with respect to airspeed, altitude, heading, and obstacle separa- tion whenever they are not in controlled airspace. Under VFR, a pilot may not ever need to speak on the radio to ATC, nor even to other pilots, and a flight plan is not required. Controlled airspace includes Class A airspace, which is that airspace from 18,000 feet to 60,000 feet, and Class B, C, and D airspace, which is airspace that surrounds larger airports and towered airports. A pilot may operate under VFR in controlled B, C, and D airspace but must follow the commands of ATC. VFR flight is prohibited in Class A airspace. There are also other specialty-use airspace categories where VFR operations are prohibited and where IFR operations are required. These airspace categories are described here in general terms, as an understanding of the full complexities of airspace regulations is not necessary for the purposes of this report. IFR and VFR define a set of rules under which a pilot operates his or her aircraft. The actual weather conditions in which the aircraft is operating are defined separately. These weather con- ditions are defined as visual meteorological conditions (VMC) and instrument meteorological conditions (IMC). Generally speaking, VMC conditions exist when the ceiling (defined as a broken or overcast cloud layer) is more than 1,000 feet and visibility is more than 3 statute miles. When the cloud and visibility conditions are better than this, VMC conditions exist, and an aircraft may be flown under VFR rules. Note that an aircraft may also be flown under IFR rules in these good conditions. However, for weather conditions less favorable than these, an aircraft may only be flown under IFR rules. Figure 2. METAR.

8 Airport Surface Weather Observation Options for General Aviation Airports The complete intricacies of VMC, IMC, VFR, and IFR are beyond the scope of this report, and are discussed here only to provide a context for how weather reporting may impact flight operations. Aviation weather systems provide outputs that help pilots determine whether VMC or IMC conditions exist (cloud height and visibility), and therefore determine whether they may operate under VFR rules, or if they must operate under IFR rules. The remaining outputs of the systems combine in various ways to affect every other aspect of flight. A generic summary of visual and instrument conditions is presented in Table 1. This sum- mary is not meant to address every condition of the aviation regulations relating to this topic but is only a guide to assist in explaining the relevance of weather conditions to certain aspects of aircraft operations. The actual visibility and cloud separation criteria differ based on the airspace classes A through G, for day and night operations, for different MSL altitudes, and even for special- use airspace conditions. Only a simplified expression of the requirements is shown in the table. In addition to the free government-supported weather services, several commercial vendors now offer fee-based weather briefings and information that may meet the requirements of 14 CFR Part 91.103. These resources have proliferated with the increased utility of smartphones and apps, which provide a scale of access beyond what might have been imagined when the Direct User Access Terminal Service (DUATS) was introduced in 1989. The FAA closed DUATS in 2018; the online option www.1800wxbrief.com, operated by Leidos, essentially duplicates the services provided by DUATS. Some representative private vendors providing aviation weather briefing and flight planning services include, but are not limited to: 1. FltPlan.com 2. ForeFlight.com 3. Garmin Pilot 4. The Weather Company (WSI) The FAA’s Advisory Circular (AC) 00-45H, Aviation Weather Services, provides a note of caution about commercial providers of aviation weather services. From this AC, Section 2.3.2— Commercial Weather Information Providers: Commercial weather information providers are a major source of weather products for the aviation community. In general, they produce proprietary weather products based on NWS information with formatting and layout modifications, but no material changes to the weather information itself. This is also referred to as “repackaging.” In other cases, commercial providers produce forecasts, analyses, and other proprietary weather prod- ucts which may substantially differ from the information contained in NWS-produced products. Opera- tors who desire to use products prepared by a commercial weather provider, as opposed to using products that are simply repackaged, may require FAA approval. This approval is granted under the provisions in Operations Specification (OpSpec) paragraph A010. Please provide which services and products you are contemplating using, to include the appropriate description of the service. This should include, but is not limited to: • The type of weather product (e.g., current weather or forecast weather); • The currency of the product (i.e., product issue and valid times); and • The relevance of the product. Pilots and operators should be cautious when using unfamiliar products, or products not supported by FAA/NWS technical specifications. Meteorological Conditions Cloud Height Visibility VFR Operations IFR Operations VMC 1,000 feet 3 statute miles Permitted Permitted IMC Any Any Prohibited Permitted Table 1. Operational conditions matrix.

Introduction 9 Additionally, the Aeronautical Information Manual (AIM), updated August 15, 2019, with Changes 1 and 2, states in section 7-1-3 “Use of Aviation Weather Products,” paragraph f: Pilots and operators should be aware that weather services provided by entities other than FAA, NWS, or their contractors may not meet FAA/NWS quality control standards. . . . Pilots and operators should be cautious when using unfamiliar products, or products not supported by FAA/NWS technical specifications. The passage further indicates that where weather information is simply a “repackaging” of approved NWS observations, the commercial provider is delivering materially the same infor- mation to a pilot as the NWS sources. However, it also indicates that commercial providers might stray from the NWS process, and if so require approval from the FAA for this deviation. The passage concludes with a warning to pilots about utilizing products not supported by the FAA and NWS. There may be significant benefits to utilizing a commercial weather service platform. These include the ability to customize products, more user-friendly graphics and interface options, and the overall utility of many app-based products that increases convenience for pilots. An addi- tional benefit could be the ability to document that a weather briefing was received in advance of a flight. This element of documentation may be important to some pilots. The Aircraft Owners and Pilots Association (AOPA) Air Safety Institute reported that in an assessment of 5,437 accidents during the period 2010 through 2013, the NTSB found no known source of a weather briefing in 1,748 (32%) of the accidents. This is not to say the required briefing was not obtained, or that weather was even a cause or factor in the accident, but the lack of documentation leaves a potential hole in the accident investigation file. For example, a self-briefing obtained at www. aviationweather.gov would typically leave no trace a pilot was there unless the pilot took addi- tional means to document it. The WXBRIEF resources do provide documentation that a briefing was received to comply with Federal Aviation Regulations (FAR). Certified aviation weather information is also important to those general aviation pilots who operate under 14 CFR Part 135, Air Carrier and Operator Certification. Despite the term “air carrier” in its title, Part 135 includes many corporate operations that are considered to be general aviation and that routinely operate at general aviation airports via corporate turbine aircraft; Part 135 aircraft must have fewer than 30 seats. Part 135 operations also include those commonly referred to as on-demand air charter or air taxi services. Weather reporting is of regulatory significance to Part 135 operators. As stated in 14 CFR Part 135.213—Weather reports and forecasts, Whenever a person operating an aircraft under this part is required to use a weather report or forecast, that person shall use that of the U.S. National Weather Service, a source approved by the U.S. National Weather Service, or a source approved by the [FAA] Administrator. However, for operations under VFR, the pilot in command may, if such a report is not available, use weather information based on that pilot’s own observations or on those of other persons competent to supply appropriate observations. For the purposes of paragraph (a) of this section, weather observations made and furnished to pilots to conduct IFR operations at an airport must be taken at the airport where those IFR operations are con- ducted, unless the Administrator issues operations specifications allowing the use of weather observations taken at a location not at the airport where the IFR operations are conducted. The Administrator issues such operations specifications when, after investigation by the U.S. National Weather Service and the responsible Flight Standards office, it is found that the standards of safety for that operation would allow the deviation from this paragraph for a particular operation for which an air carrier operating certificate or operating certificate has been issued. From a business standpoint, Part 135 operators must be able to operate in IFR conditions. This section indicates that in order for the pilot to operate under IFR rules, certified weather is required from a source at the airport, unless a waiver has been granted by the FAA Administrator.

10 Airport Surface Weather Observation Options for General Aviation Airports Furthermore, 14 CFR Part 135.225—IFR takeoff, approach and landing minimums, states: a) Except to the extent permitted by paragraphs (b) and (j) of this section, no pilot may begin an instrument approach procedure to an airport unless— 1. That airport has a weather reporting facility operated by the U.S. National Weather Service, a source approved by U.S. National Weather Service, or a source approved by the Administrator; and 2. The latest weather report issued by that weather reporting facility indicates that weather condi- tions are at or above the authorized IFR landing minimums for that airport. b) A pilot conducting an eligible on-demand operation may begin and conduct an instrument approach procedure to an airport that does not have a weather reporting facility operated by the U.S. National Weather Service, a source approved by the U.S. National Weather Service, or a source approved by the Administrator if— 1. The alternate airport has a weather reporting facility operated by the U.S. National Weather Service, a source approved by the U.S. National Weather Service, or a source approved by the Administrator; and 2. The latest weather report issued by the weather reporting facility includes a current local altimeter setting for the destination airport. If no local altimeter setting for the destination airport is available, the pilot may use the current altimeter setting provided by the facility designated on the approach chart for the destination airport. While the totality of the Part 135 regulations are complex, their dependence on certified weather broadcasting at the point of landing or departure, or as allowed at the alternate airport, is clear in these sections. Without access to certified weather information, a general aviation airport cannot fully serve the Part 135 community. The FAA Reauthorization Act of 2018 includes language that slightly modifies some of the requirements for Part 135 operations in noncontiguous states (Alaska and Hawaii). In addition to this new guidance, the FARs already contain numerous operational modifications specific to Alaska in recognition of the unique challenges posed by the climate and topography of the state. Similar to Part 135, 14 CFR Part 91, Subpart K—Fractional ownership operations (Part 91K) operations are of great importance to general aviation airports. Examples of Part 91K opera- tions include services provided by NetJets, Flexjet, Jet Alliance, and AirShare. Note that these companies may also operate under Part 135. Part 91K includes weather information require- ments similar to those in Part 135. According to 14 CFR Part 91.1039—IFR takeoff, approach and landing minimums: (a) No pilot on a program aircraft operating a program flight may begin an instrument approach procedure to an airport unless— 1. Either that airport or the alternate airport has a weather reporting facility operated by the U.S. National Weather Service, a source approved by the U.S. National Weather Service, or a source approved by the Administrator; and 2. The latest weather report issued by the weather reporting facility includes a current local altimeter setting for the destination airport. If no local altimeter setting is available at the destination air- port, the pilot must obtain the current local altimeter setting from a source provided by the facility designated on the approach chart for the destination airport. (b) For flight planning purposes, if the destination airport does not have a weather reporting facility described in paragraph (a)(1) of this section, the pilot must designate as an alternate an airport that has a weather reporting facility meeting that criteria. Thus, the availability of certified weather is vital to the reliable and legal operations of fractional ownership general aviation aircraft. The information provided above has demonstrated the importance of weather information to the general aviation pilot, discussed the broad regulatory framework for aviation weather data management, and provided a brief description of the dissemination of aviation weather information to users. Airport surface weather observation systems provide one of many important data inputs used to support aviation weather reporting products. These systems are most commonly

Introduction 11 located at airports, with the majority of them located at airports that serve general aviation operations exclusively. General aviation aircraft operators and general aviation airport staff have thousands of interactions with these systems daily. For this synthesis, a survey was taken of general aviation airports across the country to gather data on their system types, uses, costs, reliability, and other factors. An attempt was made to include diversity in terms of airport size, geographic location, climate, and system types. This synthesis addresses surface weather observation systems at general aviation airports. This report will present a brief history of aviation weather; identify the current documents and regulations that govern surface weather observation systems; identify the current state of technology in the industry; and present case examples of interesting experiences relating to surface observation systems in use at both general aviation airports and other diverse locations. Systems assessed will include both those that the FAA has certified to provide approved weather data to the NAS and those that are not certified but that still contribute advisory data through nongovernmental channels, and that pilots may utilize in a variety of ways. Background Weather observation in the United States began in 1849, when the Smithsonian Institution provided weather instruments to the telegraph companies, establishing the first observation network (Figure 3). The Smithsonian compiled those observations and used them to create the first weather maps. According to the National Weather Service (NWS), the first use of weather in aviation was when the Wright Brothers consulted what was then the Weather Bureau to deter- mine a suitable location to conduct their early testing. In 1914 the first government agency dedicated to aviation weather was developed when an aeronautical section was established within the U.S. Weather Bureau and began issuing aviation- related weather bulletins and forecasts for military and air mail service. The U.S. government’s continued investment in aviation weather throughout the 20th century is demonstrated in the timeline in Figure 4. Source: National Weather Service, Cheyenne, Wyoming. Figure 3. “Wyoming wind sock” sign parodies weather observation instruments, claiming that it can report the weather through the angle of its chain.

12 Airport Surface Weather Observation Options for General Aviation Airports Figure 4. Aviation weather services: historic timeline.

Introduction 13 In the 1980s DOD, the NWS, and the FAA began to invest heavily in automated weather observation systems. In 1989, a plan to modernize the NWS included replacing manual weather observation with ASOS systems. According to the NOAA website, since that time, more than 900 ASOS systems, 260 FAA-owned AWOS systems, and more than 1,000 airport-owned or privately owned AWOS systems have been installed at airports throughout the United States, making those airports more accessible for pilots who are flying approach procedures that require certified weather sources. Certified automated systems are not the only source of weather observation. There are sev- eral lower-cost advisory systems that, for some airports, provide excellent options due to lower acquisition and maintenance costs and are often sufficient to support aircraft that do not rely on instrument procedures. An advisory observation can be anything from a universal communica- tions (UNICOM) operator relaying (visual) windsock information to a system that has most or all of the capabilities of an AWOS III but is not certified. There can also be unique needs that are driven by geographic or climatic peculiarities. The state of Colorado has installed AWOS systems in select passes along the Continental Divide to provide pilots with information in areas subject to rapidly changing conditions and challenging navigation. Alaska has many remote airports, few roads, and relatively few certified weather systems. Very often the solution has been to “just fly out and take a look.” To provide pilots with the ability to remotely observe airport conditions, the FAA installed cameras at almost 300 air- ports. The cameras are linked to a sophisticated website that allows pilots to view the conditions at their destination, as well as at several passes and key locations, without leaving the ground. Modern technology continues to improve the accessibility of airport weather information. Leidos now has a website that provides the type of services previously available by calling their 1-800 telephone number. Several private applications provide weather and flight planning access by smartphone, tablet, or smart watch. In the air, GA pilots can access weather and air traffic information through XM radio subscriptions or ADS-B to obtain observation of the weather con- ditions along their routes and allow for early diversions to avoid flying into significant weather. With the proliferation of the Global Positioning System (GPS), instrument approaches to an airport no longer require expensive ground-based equipment. This has allowed for instrument approaches to be developed for numerous GA airports, making them more accessible to the fly- ing public. The availability and proximity of certified weather information is a key component in fully utilizing these approaches. Automated weather systems have been valuable tools in improving the safety and usability of the National Aviation System. Objectives This synthesis will identify the different types of surface observation systems available to air- ports, the types of operations each sensor can support, and the different factors to consider when acquiring surface observation equipment. This report is intended to provide general aviation airport personnel with an expanded context of how surface observation systems fit within the national airspace system and to assist them in making an informed purchasing decision for a system that meets their needs. Approach The project began with a preliminary literature review to gain a better understanding of the topic and the type of information that was available to the industry. This review included the relevant advisory circulars and FAA orders covering the installation and operation of weather systems, lists of approved equipment, and manufacturer’s literature on these products.

14 Airport Surface Weather Observation Options for General Aviation Airports A brainstorming session was completed with relevant participants to determine data to be acquired, the target audience for the survey, and nonparticipant experts who could be contacted. All of these were completed while remaining focused on the synthesis scope and the initial ACRP panel comments received. A list of potential survey recipients was developed based on climatic and geographic diver- sity. This list included general aviation airports that had purchased or upgraded a weather system under the Airport Improvement Program (AIP) within the past 8 years. The list was further expanded by reviewing FAA databases for airports with an existing weather system while eliminating those without significant facilities or based aircraft. This resulted in an initial list of 32 potential participants. The six survey regions were identified using the FAA Regions as a guide: 1. Northeast and Great Lakes Region 2. Southeast Region 3. Southwest Region 4. Great Plains and Central Region 5. Rocky Mountain Region 6. Pacific Northwest Region Due to the unique characteristics of Alaska’s aviation environment, Alaska is discussed as a case study. Each airport on the initial participant list was contacted by telephone as part of a pre- screening process. Potential survey participants were informed of the scope and purpose of the study and asked if they were willing to participate. The survey was distributed to willing participants through an online service. Of 32 airports contacted, 27 responded to the survey, for an 84.4% response rate. Figure 5 shows the locations of the respondents. The survey responses were reviewed to identify good candidates for further interviews to develop into case examples. The literature review continued concurrently with the survey process, and as gaps were iden- tified in the research, subject matter experts were contacted as part of the industry outreach. Table 2 presents some details about the participating airports. Figure 5. Survey respondents map.

Introduction 15 Table 2. Airports that participated in the survey. ID Airport Name State Annual Operations Longest Runway Weather Station Type 67L Mesquite Airport NV 7,004 5,121 AWOS II AHQ Wahoo Municipal Airport NE 16,350 4,100 AWOS III P ANQ Tri-State Steuben County Airport IN 5,959 4,540 AWOS III BTP Pittsburgh/Butler Regional Airport PA 74,356 4,801 AWOS III P/T COE Coeur d’Alene Airport ID 123,048 7,400 AWOS III P/T EEN Dillant-Hopkins Airport NH 26,600 6,201 AWOS III P/T FDK Frederick Municipal Airport MD 94,901 5,219 AWOS III P/T GDV Dawson Community Airport MT 5,800 5,704 AWOS III P/T GNG Gooding Municipal Airport ID 26,800 4,745 AWOS III P/T JAQ Westover Field Amador County CA 25,000 3,401 AWOS III JKA Jack Edwards National Airport AL 92,912 6,962 AWOS III P/T LAM Los Alamos Airport NM 14,340 6,000 AWOS III P M40 Monroe County Airport MS 12,814 4,999 AWOS III P M46 Colstrip Airport MT 1,450 5,100 AWOS A/V N27 Bradford County Airport PA 23,100 4,301 AWOS A/V O85 Benton Field Airport CA 37,000 2,420 AWOS II OKV Winchester Regional Airport VA 44,115 5,498 AWOS III P RCE Clarence E Page Municipal Airport OK 42,554 6,014 AWOS III RTS Reno/Stead Airport NV 57,300 9,000 AWOS III S40 Prosser Airport WA 13,200 3,452 AWOS I SRE Seminole Municipal Airport OK 17,150 5,004 AWOS IIIP/T SUZ Saline County Regional Airport AR 45,500 5,002 AWOS III TDW Tradewind Airport TX 27,325 5,098 AWOS A/V UYF Madison County Airport OH 41,410 4,001 AWOS III P/T VEL Vernal Regional Airport UT 8,960 7,000 ASOS VJI Virginia Highlands Airport VA 26,631 4,471 AWOS III ZPH Zephyrhills Municipal Airport FL 49,425 5,000 AWOS III P/T Note: Annual operations as reported by AirportIQ 5010 at https://www.gcr1.com/5010WEB/ on February 26, 2019. Data may not represent the most current 12-month period. Report Structure This report is organized in six chapters with a summary, glossary, references, and two appen- dices. Chapter 2 provides a summary of the literature review. Chapter 3 presents the results of the survey, with conclusions discussed later in Chapter 6. Chapter 4 discusses the state of the existing technologies for surface weather systems today. Chapter 5 presents case examples based on follow-up interviews after the survey. Chapter 6 offers conclusions and recommendations for future study. The online survey is included in the appendices.

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The needs of airports may vary depending on the types of operations typically conducted at the airport, as well as the type of weather common to the airport.

The TRB Airport Cooperative Research Program's ACRP Syntheis 105: Airport Surface Weather Observation Options for General Aviation Airports aims to provide the operators of general aviation (GA) airports a comprehensive source of information about airport-based weather observation options so they may make informed decisions to support the specific operational needs of their airport.

Weather observations at airports can come from either FAA-approved (certified) or advisory (non-certified) sources. Weather reporting at a GA airport, whether certified or not, typically comes from automated sources, as human observers are increasingly being phased out or are stationed mainly at commercial service airports.

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