Drones, Helping To Clear The Way For Airplanes In Wisconsin

by Hal Davis
WisDOT Bureau of Aeronautics
Published in Midwest Flyer Magazine – December 2021/January 2022 Online Issue

For pilots, a freshly paved runway or new terminal building are airport improvements that are easy to recognize and appreciate. Conversely, obstruction clearing can be one of the most challenging improvements made at an airport, but often goes unnoticed by airport users. While many parts of Wisconsin are home to pristine forests, trees close to the runway can pose a hazard to aircraft. We may think of ourselves as capable backcountry pilots, but the truth is, a shallow, stable approach to the runway is generally safest for most pilots and aircraft. Clear approaches also increase the margin for error during the most critical phases of flight, which is especially important in poor weather conditions. For these reasons, identifying and mitigating trees and other obstructions is a never-ending project for many Wisconsin airports.

In Wisconsin, we require all public-use airports to provide a clear 20:1 approach slope to the runway threshold. This means for every 20 horizontal feet you move away from the threshold, the allowable height increases by 1 foot. For example, a tree 200 feet from the threshold can be a maximum height of 10 feet above the threshold elevation. For runways that serve larger aircraft and/or have instrument approach procedures, the slope is even shallower, and the size of the approach area is increased to provide an even greater margin for error.

To ensure compliance and help airports identify potential problems, the Wisconsin Bureau of Aeronautics (BOA) inspects all public-use airports at a minimum of once every three years. Historically, inspectors utilized simple ground-based tools to identify potential obstructions. These tools are excellent at quickly determining if a problem exists but struggle to provide a complete and accurate picture. To overcome these shortcomings, BOA has acquired a specialized drone which can conduct obstruction surveys from the air.

The process first involves digitally mapping the extent of the survey area and checking for potential flight conflicts with Federal Aviation Regulation Part 107. Flight planning software is then used to set mission parameters and create the drone’s flight path. Once on location, the drone autonomously flies the mission, usually at 300 feet above the ground, and takes hundreds of precisely georeferenced photos along the way. During the flight, real-time positional corrections are provided to the drone via a high-precision Global Navigation Satellite System (GNSS) base station, and ground control points are used for further data refinement during post-processing. Back in the office, specialized software stitches the images together into both a 2D orthomosaic map and a 3D model upon which further analysis can be performed.

The advantages of utilizing the drone are significant. Whereas previous obstruction evaluations were limited to line of sight from the ground, this process allows the inspector to comprehensively evaluate the entire approach area. In addition, data accuracy is improved over previous collection methods. Finally, additional analysis of the data can answer important questions like whose property is the obstruction on and how many trees need to be cleared. Useful maps can also be created to aid in obstruction reporting, decision-making, and eventually mitigation.

Although the proliferation of unmanned aircraft continues to present challenges to traditional manned aircraft operations, drones are here to stay. Fortunately, new innovations in drone technology should continue to improve our daily lives. We at the BOA think drones should be used to improve our lives as aviators as well and using drones to help clear approaches for aircraft is only step one.

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