Benefits of Using Drones at Aircraft Accident Sites
With the creation of the Aircraft Accident Investigation Authority (AAIA) to investigate aviation accident and incidents in the Bahamas, one of the latest use of technology in our arsenal, is the introduction of Aerial images of accident sites as part of our investigative tool.
The AAIA recently signed a memorandum of understanding with FlyyTec Ltd. for the use of its drone technology to assist in the investigation of aircraft accidents and incidents. The use of drones are essential for a number of reasons.
They can capture the whole site from the initial impact point to the wreckage’s final resting location.
The ground marks and wreckage distribution help to identify how the aircraft hit the ground.
Aerial images are also useful for showing the relative positions of obstacles, such as trees or buildings that may have been struck before ground impact.
They help to reveal the surrounding terrain and environment that the pilot faced if there was an attempted forced landing.
And when it’s a large aircraft at an accident site, aerial images help to document the damage to its upper surfaces.
The AAIA has, in the past, been primarily reliant on helicopters and sometimes search-and-rescue aircraft to obtain aerial images. These images have been useful but did not always capture the angle or detail required. Previously the AAIA would charter an aircraft, if the accident or incident occurred in one of the family islands, and prior to landing got aerial imaging. This method was expensive, not very useful, (because of the speed of the aircraft), unsafe, (because the aircraft would have to slow or conduct maneuvers which could be dangerous) and took time to organize.
About three years ago, it was noticed that small unmanned aerial vehicles (UAVs), or drones as they’re now more commonly referred to, had become significantly less expensive and could provide aerial images within minutes of arriving at an accident site. Having the investigator controlling the drone’s camera, all the angles and details needed are captured.
The AAIA bought their first drone, a DJI Phantom 2 Vision in February 2017 which it intended to use to capture aerial photos of accident sites. As the AAIA was new to drone technology at the time of the documented accident, FlyyTec Ltd. was engaged to provide aerial photography and video documentation of an accident site on June 8, 2018 (Figure below).
The drone’s 14-megapixel camera provided excellent stills and video quality. As well as taking stable video, the additional benefit of the drone model used was that the camera could be tilted 90 degrees downwards to take a series of overlapping images to map the whole accident site.
The expectation was to be able to use photo-stitching software to stitch all the images together. This led to exploration of what photogrammetry software could do. Not only could it generate 3D models from a series of overlapping images, but it could also create a stitched overhead image that was true to scale; an image that is called an orthomosaic.
The AAIA again on March 21, 2020 utilized drone Technology by FlyyTec Ltd. to Map out and document overhead and all point photo documentation as the aircraft was in waters and inaccessible by investigators.
Benefits of drones for accident site imagery
The main benefits of using drones over manned airplanes or helicopters are:
● Significantly lower cost (a suitable drone can be obtained for about $800).
● Drones can be deployed immediately on arrival at site.
● The images and video from the drone can be viewed live on the ground.
● The investigator has full control over the images and videos that are taken.
● A drone can be easily relaunched to take additional footage.
● A drone can be flown closely to trees and wreckage to obtain close-up images without disturbing them with rotor downwash.
● A drone can be easily programed to take a series of geo-tagged and overlapping overhead shots for photogrammetry purposes.
● A drone can operate in low-visibility and low-cloud conditions that would prevent an airplane or helicopter being operated.
The uses so far identified for drones at accident sites are:
● Wreckage and site survey,
● Wreckage search,
● Tree/object height estimations,
● Site safety assessments, and
● Flight path reconstruction/visualization.
Also, with the introduction of underwater drones, underwater debris field can be more accurately documented. The time it takes for divers to physically photograph a debris field, the drone can accomplish this in a much shorter time and in a safer environment without the need to constantly resurface or the concern for underwater
creatures that may pose a threat to the unsuspecting divers.
The photogrammetry software that FlyyTec Ltd. uses is called Pix4Dmapper Pro. This provided some good photogrammetry results using the drone. In September 2015 the FlyyTec Ltd. upgraded to the DJI Inspire Pro drone which can operate in winds up to 20 kt and has a higher quality camera that can stream high-definition (HD) video to two tablet devices. This model is also available with dual controls for the pilot and camera operator.
How FlyyTec Ltd. operates drones Under Bahamas regulations, the FlyyTec Ltd. is not classed as a commercial operator flying for reward so they can operate drones at accident sites under the standard regulations for recreational users. The main limits are maintaining visual line-of-sight, a minimum distance of 50 meters from people, buildings, and vehicles that are not under our control, and 150 meters from congested areas. Since operations are primarily inside a police cordon where everyone can be under our control, these limits have not been a restriction.
The FlyyTec Ltd. operations manual lists flight limitations and training and currency requirements for their operators. The two main operators are FlyyTec Ltd. engineering support staff. One of the operators will normally deploy to an accident site to assist with wreckage recovery and will fly the drone. The investigator onsite will normally operate the camera. FlyyTec Ltd. requires two people to operate the drone, because to fly the drone safely the pilot needs to be heads up watching the drone and looking out for obstructions and people. To take good pictures, you need to be heads down. The only time single-operator flight is allowed is when the drone has been programmed to fly an automated route and automatically take stills; in this case, the operator is monitoring the flight and is able to override the autopilot.
Creating orthomosaic images and 3D models of accident sites
With photogrammetry software like Pix4Dmapper Pro orthomosaic images and 3D models of accident sites can be produced using drone imagery. An orthomosaic is an image that is composed of multiple overhead images and is corrected for both perspective and scale, which means that it has the same lack of distortion as a map.
The images are obtained by pre-programming the drone to fly in a grid pattern and to automatically take a series of overlapping shots with the camera pointing 90º down.
The photogrammetry software also generates a 3D point cloud and a 3D mesh from the images. The 3D model can be used to take measurements of the site. In trials measurement, accuracies of up to 1 cm using drone images captured from a height of 40 m have been obtained.
Benefits of photogrammetry software for processing accident site imagery
Taking aerial images of an accident site and processing them with photogrammetry software has a number of benefits.
● The 3D model is very useful for briefing people who have not attended the accident site. You can manually zoom in and out and rotate the model to show all the ground marks and wreckage distribution. This can make it easier for people to visualize the site compared to flicking through a number of still images.
● Pix4D can be used to create an animated video of the 3D model that can then be sent to people to view who do not have the Pix4D software.
● If some time has passed between attending the accident site and writing the report, then viewing the 3D model can serve as a useful refresher.
● The orthomosaic images serve as a very detailed wreckage plot.
● Measurements of the site can be made using the 3D model or orthomosaic that are more accurate than using a hand-held GPS, and can be up to 1 cm in accuracy.
● The orthomosaic is also a useful tool to search for missing wreckage and it can be reviewed in slow time back in the hotel or office.
The AAIA has found drones to be a very useful tool at accident sites. They are very good for capturing the scene before we start disturbing it. Drones can access areas unsafe for investigators as in the cases involving crash in water, in dense bushes or in accidents involving fire.