3D Modeling: A Valuable Investigative Tool

By Michael Bauer

On February 10, 2018, an air tour helicopter descended into a canyon wash and collided with terrain while on approach to land at Quartermaster landing zone in the Grand Canyon near Peach Springs, Arizona. As part of this ongoing investigation, NTSB engineers needed a three-dimensional (3D) digital model of the accident site and surrounding terrain to thoroughly understand the terrain features in the local area. Although the main effort involved the use of a FARO laser scanner to create the 3D model, the NTSB small unmanned aircraft systems (sUAS) team recognized an opportunity to exercise our sUAS imagery-collection capabilities using photogrammetry and sUAS in a challenging environment to support this investigation and allow for a comparison of the data gathered from the two techniques for future investigations.

Map1
Excerpt from Grand Canyon VFR Aeronautical Chart (FAA)

Since 2016, the NTSB has used sUASs, or drones, to create orthomosaic maps of wreckage sites and provide 3D digital models of terrain and vehicles for use by investigators in all transportation modes. Recently, we’ve launched the drone team to rail accidents (including the Hyndman, Pennsylvania, and Alexandria, Virginia derailments) highway crashes (including the Amtrak grade crossing collision with a refuse truck in Crozet, Virginia), and aviation accidents (including the crash of a cargo airplane in Charleston, West Virginia; the rejected takeoff and runway excursion at Willow Run Airport in Ypsilanti, Michigan; and multiple general aviation accidents at sites across the country). None of these missions, however, presented terrain challenges like those in the Grand Canyon.

Because the Grand Canyon is a combination of National Park Service and tribal lands, planning for the mission started weeks in advance. We needed to obtain permission from various tribal and governmental entities to operate a drone within that airspace and the special flight rules area (SFRA). The area is heavily used by numerous helicopter tour operators in the region, so planning involved coordinating with and notifying the various local operators of our intended sUAS mission. Without the support of the Federal Aviation Administration, the Hualapai Nation, the National Park Service, and Papillion Helicopters, this mission wouldn’t have left the ground.

After we received the appropriate approvals, we assembled in Boulder City, Nevada, to load a helicopter for the short trip into the canyon. Unlike other sUAS missions I’ve conducted, the remoteness of the canyon location introduced many challenges. For example, at the site, there were no electrical outlets or a generator, so we needed to plan the mission carefully in advance to ensure that it could be completed within the flight time enabled by the available batteries—recharging was not an option. Also, cellular coverage (including wifi) was nonexistent; thus, we had to access the Internet for the ground station software before departing for the canyon. In addition, when we use the sUAS to map an accident site, we use ground control points (GCPs) that we typically mark with paint. However, out of respect for the sacred land of the Hualapai Nation where the operation took place, we instead used lightweight, removable targets as GCPs. In total, I took 65 pounds of gear into the canyon to support the sUAS operation.

 

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We conducted the sUAS flight early in the morning in light wind conditions suitable for drone flying and low temperatures, which was welcome compared to the triple-digit temperatures expected later in the day. We conducted our flights concurrent with the laser‑scanning effort in the canyon wash. As remote pilot in command (RPIC), I arranged for our helicopter pilot to work with me as the visual observer (VO) for the mission. The VO monitored the local traffic frequency for inbound and outbound traffic and relayed information back to me. During a few flights, I paused the mission to land the drone to ensure safe separation from tour helicopters. We accomplished the mission in just over an hour of sUAS flying time, which included a 12-minute, 10-acre mapping mission. The effort provided a detailed 3D model of the canyon wash for the engineers and stunning visual imagery of the local terrain area. The data are currently being analyzed by investigative staff.

Figure 3
NTSB sUAS flying in the Grand Canyon

Through this investigation and others, we’ve found that the ability to create 3D models of accident scenes is a valuable tool in the investigator’s tool box. Moreover, the ability of the sUAS to provide the imagery needed for these models in unique, complex environments in a short time and with low acquisition cost will aid our investigators for years to come. The NTSB sUAS team continues to explore the possibilities of sUAS imagery collection within the envelope of safe drone operations to further understand the capabilities and limitations of the technologies as they relate to the agency’s mission.

Michael Bauer is an aerospace engineering investigator in the NTSB Office of Aviation Safety.

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