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1 The purpose of this synthesis report is 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. Airportsâ needs 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 report was developed using information obtained through a comprehensive litera- ture review, outreach to various stakeholders, guidance by the study panel members, tele- phone interviews, and surveys distributed to geographically diverse airports that use various types of weather observation systems. General aviation aircraft make up the majority of the aircraft fleet and also account for the majority of operations in the national airspace system. General aviation aircraft operate from a wide variety of landing surfaces and in all climates and are exposed to every conceiv- able weather phenomenon. However, due to their generally smaller size and lower sophisti- cation in comparison with the commercial fleet, GA aircraft are at a higher risk from severe weather. Given this broad exposure to weather and the risks that weather can present to smaller aircraft, access to accurate weather information can become critical to operations at the airports most often utilized by these aircraft. Weather observations at airports can come from either FAA-approved (certified) or advisory (noncertified) 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. Certified automated sources primarily include the Automated Weather Observing System (AWOS) and the Automated Surface Observing System (ASOS). While more than 900 ASOS systems are in operation, they are no longer being installed. AWOS systems exist in a variety of configurations. The most basic, AWOS A, reports only an altimeter setting. The most advanced system is the AWOS IV Z/R, which can identify several types of precipitation as well as report runway conditions. The most common instal- lation is the AWOS III and its variants, AWOS III P, AWOS III T, and AWOS III P/T. Both the AWOS III (or higher) and ASOS report the following minimum information: â¢ Temperature â¢ Dew point â¢ Wind direction and wind speed â¢ Precipitation â¢ Cloud cover and cloud height â¢ Visibility â¢ Barometric pressure S U M M A R Y Airport Surface Weather Observation Options for General Aviation Airports
2 Airport Surface Weather Observation Options for General Aviation Airports This information constitutes the minimum information required to assemble a standard aviation weather report called a Meteorological Terminal Aviation Routine Weather Report, or METAR. The METAR is transmitted through the National Airspace Data Interchange Network (NADIN) to a data collection and dissemination network called the Weather Message Switching Center Replacement (WMSCR). Certified data provided by the WMSCR is the only aviation weather information that is legal for aircraft operational and safety-of- flight decisions. This data may be accessed by pilots through federal weather providers, FAA flight service stations, and various private airport weather providers. Certified METARs are also typically available directly from the ASOS/AWOS itself through a radio broadcast to aircraft or by telephone. Only AWOS systems rated AWOS III or higher are eligible to report to the WMSCR. All ASOS systems are owned and operated by the federal government. Some AWOS systems are also owned and operated by the federal government, but the majority of existing AWOS systems and all new AWOS systems installed today are primarily owned and operated by the airport or, less commonly, by another government or private entity. A planning-level estimate for the construction of a new AWOS III system is approxi- mately $250,000 for an installation that requires only minimal site work. Additional costs would include those necessary to design, procure, and inspect the system; these may exceed $50,000. Annual recurring costs for required inspections and operations are estimated at $7,000 per year. Grant funding for installation is available through the FAA, some state agencies, and various other sources. Some state funding programs support inspection and maintenance requirements. The FAA does not support inspections or system maintenance. All pilots, regardless of the type of flight, have a regulatory obligation to become familiar with the weather along their proposed route and at their destination airport. Additionally, certain types of operations have specific requirements for the use of certified weather in making flight decisions. For airports supporting business, charter, and fractional ownership operations, the availability of certified weather is vital. For some GA airports, advisory weather from a noncertified system may be adequate. The airport may be limited in the types of operations that it can accommodate or it may be located in an area without much demand for higher-performance aircraft, and therefore certified weather may not provide much, if any, operational benefit. Noncertified systems are not manufactured, installed, or inspected to any federal standards. However, they may still provide sufficient information to adequately support the operations at an airport. Non- certified system information cannot be accessed through the WMSCR and is not typically available on a national scale, as certified data is. Access to noncertified systems is typically over a discrete VHF frequency or the airportâs universal communications (UNICOM) frequency, by telephone, or on airport or third- party websites. The reports these systems generate can mimic a METAR, and the informa- tion they report may be as accurate as that of a certified system; however, the reports do not satisfy the regulatory requirements for most business, charter, or fractional ownership operations conducted under Title 14 of the Code of Federal Regulations (14 CFR) Part 91 and Part 135. Noncertified systems can cost as little as $5,000, and some are eligible for state grant fund- ing, although typically not federal funding. Installation is typically much less expensive than for certified systems because the equipment itself it usually less costly, and there are fewer siting and installation requirements. Operational expenses are minimal, with no mandated inspections.
Summary 3 In addition to advisory automated weather reporting, weather cameras can provide the pilot with a visual reference to weather conditions at a destination airport. The most com- prehensive camera installation is the FAAâs Alaska Weather Camera Program, which uses a website that allows pilots access to all types of weather information from around the state. While the information provided by the cameras themselves is considered supplemental (i.e., advisory) to approved weather, it does afford a certain increased level of safety in an area with few certified weather sources and the potential for rapidly changing weather conditions. Additional information relating to weather reporting systems at general aviation airports includes: â¢ Only those certified systems capable of producing a complete METAR are eligible to report to the WMSCR. This means that systems rated AWOS II or below do not report to the WMSCR. â¢ The results of a nationwide survey of general aviation airports indicates that there exists some confusion as to the differences between certified and noncertified aviation weather systems, as well as the costs to install and maintain them. â¢ Evolution of the technology used in certified systems has been slow since its widespread adoption in the 1990s. This can create some operational hurdles, such as frequency con- gestion and limited competition among manufacturers. â¢ The siting and operation of certified systems can present some unique challenges for gen- eral aviation airports, particularly those with limited land. The case examples presented in this report provide illustrations of many unanticipated conflicts. â¢ The use of certified equipment will provide a broader national dissemination of an air- portâs weather data and will also allow for that data to be used for legal flight planning and other operational decisions by aircraft. â¢ Aviation weather data may provide broader benefits to both the national airspace system and public safety beyond those strictly related to the operations at the airport where the system is based. One example of this is the support of air ambulance services, which rely on a broad network of weather data to operate over unfamiliar terrain and at unpredict- able times. â¢ The use of weather cameras is expanding, and greater implementation and data dissemi- nation could expand the utility of surface weather reporting at airports. Alaska maintains the most robust weather camera network in the country. Weather camera data is still considered as advisory only.