Counting Aircraft Operations at Non-Towered Airports (2007)

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Annual aircraft operations estimates are used in aviation system planning, airport master planning, environmental studies, aviation forecasts, and to determine funding and design criteria for the nation’s airports. At airports with air traffic control towers, aircraft opera- tions are tracked and recorded by the air traffic controller. Most airports in the United States, however, do not have air traffic control towers. These airports are generally known as non- towered airports, and they make up the vast majority of the airports open to the public for business. Accordingly, unlike with larger towered airports, these non-towered airports do not have readily available records on aircraft activity. Consequently, many state aviation agencies and some airports and metropolitan planning organizations (MPOs) have devel- oped aircraft traffic counting programs to track airport activity at their airports. However, many have not. For airports without air traffic control towers and/or with part-time towers, the number and type of operations may be based on the best guess of the airport manager or on prior-year counts, factored for assumed growth. It would be desirable to know and use the most accurate means of counting and estimating actual operations at these smaller air- ports. The corresponding operations data collected could then be included on FAA Airport Master Record Form 5010, because this form is often used as a source for these data in the system planning, master planning, forecasting, and funding operations. This synthesis project determines the practices for counting and estimating aircraft oper- ations at non-towered airports. A literature review was conducted to establish previous research and findings on counting and estimating aircraft operations at these airports. Addi- tionally, questionnaires were sent to all 50 state aviation agencies and selected airports and MPOs that were known to have traffic counting programs to determine their methods of counting and estimating aircraft operations at non-towered airports. A total of 61 question- naires were sent and 51 were returned, an 84% response rate. Crossover technology was researched and traffic counting manufacturers and aviation trade organizations were also contacted. This was done to help determine current and potential technology for counting and estimating aircraft operations and also to help obtain previous research completed on the topic. Through this synthesis report it was revealed that a variety of methods are being used across the country to count and estimate aircraft operations, and these methods vary in accuracy. These methods are: • Count traffic year-round, • Sample traffic and extrapolate annual operations, • Multiply a predetermined number of operations per based aircraft by the total aircraft based at the airport, • Perform regression analysis, and • Ask the airport manager or personnel associated with the airport. The most common method used by the respondents to this study’s questionnaire is also the most inaccurate of the methods currently in use, which is simply asking the airport SUMMARY COUNTING AIRCRAFT OPERATIONS AT NON-TOWERED AIRPORTS

manager or other related airport personnel what they believe the annual aircraft operations are for their airport. The Texas Department of Transportation’s 1994 Aircraft Activity Counter Report found that an airport’s operations can be as much as doubled when esti- mated by the airport manager as opposed to sampling traffic with an acoustical counter and extrapolating the sample into an annual estimate. The most accurate method currently in use is to deploy an aircraft traffic counter(s) at an airport year-round, which in theory counts all traffic at the airport. Seven respondents used this method, four of which were airports. Another method believed to be accurate is to sample traffic with some type of aircraft counter for two weeks in each of the four seasons and to expand that sample into an annual count. The method relies on a valid extrapolation from the sample to annual operations. How- ever, only 6 of the remaining 12 respondents that sampled traffic actually did so for two weeks in each of the four seasons. The final six did not sample in all four seasons, making their results less accurate than those that sampled during all seasons or year-round. The method used to expand the sample count to an annual estimate was most often done with a seasonal or monthly adjustment factor. How the adjustment factor was determined for each respondent was not covered in this study’s questionnaire and is recommended for further study. Previous research indicated that towered airports were not a valid way to develop adjustment factors for non-towered airports partially because of the availability of more instrument approaches at towered airports, which supposedly made them accessible during inclement weather. This may have been the case more than 20 years ago, but more and more non-towered airports have instrument approaches today. There are currently six different methods being used to sample aircraft traffic: • Acoustical, • Airport guest logs, • Fuel sales, • Pneumatic, • Video image detection, and • Visual. Use of airport guest logs and fuel sales, although helpful, will not track all traffic because not all pilots sign a guest log and because not all aircraft purchase fuel with each flight. Additionally, neither of these methods will account for touch-and-go operations. Of the equipment currently being used to sample traffic, the acoustical (including the sound- level meter and computerized acoustical) and video image detection systems offer acceptable levels of accuracy in detecting aircraft, both estimated by the manufacturers to be in the 90% range. The acoustical systems are generally less expensive than the video systems, although the video systems offer more information such as aircraft tail numbers. Visual sampling of traffic by a human observer is very accurate, but also very costly and time-consuming. In summary, it is believed that the most accurate and cost-effective way to estimate air- craft operations at a non-towered airport is to sample traffic for two weeks for each of the four seasons and extrapolate that sample into an annual estimate. This would be considered the best practice if year-round counts are not feasible. As stated earlier, the acoustical counter provides a cost-effective, efficient, and accurate way to collect the sample, whereas the video image detection system, although more costly, adds additional information that may be use- ful to the airport. Pneumatic counters and inductance loop counters have several serious limitations and would only be useful at airports that have a most simple configuration of one runway and one entry taxiway. Airport guest logs and fuel sales are also not recommended as a way to count traffic. 2

The information received by the states, airports, and MPOs from their aircraft traffic counting programs is being used for a variety of purposes, including justification for airport improvement projects, justification for air traffic control towers, airport environmental documentation, forecasting, economic impact statements, performance measures, FAA Airport Master Record Form 5010 reporting, system planning, justification for navigational aids, and airport planning studies. Because the most common method for estimating aircraft operations (asking the airport manager or other airport personnel) may not be accurate, the information being used for these purposes may also be assumed not to be accurate. Addi- tionally, because the methods being used to count and estimate aircraft operations at non- towered airports vary in accuracy, the results are not comparable among the airports. As stated earlier, airport operations data are being used on FAA Airport Master Record 5010 forms. Each airport has an Airport Master Record that is produced under the guide- lines of the FAA Airport Safety Data Program. The information on the Airport Master Record is made available to the general public to use at their discretion. The FAA Order directs the airport inspector to record the total number of general aviation operations that occur at the airport. It further stipulates that the inspector is to use “FAA tower counts where available. If not available from FAA sources, use estimates based on discussion with airport management and/or the fixed base operators.” State aviation agencies and the FAA should coordinate the collection and reporting of accurate airport operations data. This can be accomplished by: (1) encouraging widespread use of appropriate practices identified in the synthesis; (2) when such practices are used, including information in the Airport Master Record Form 5010; and (3) considering changing the format of Form 5010 to identify the counting practices used. 3