Drone Test Methods Help Practice Critical Rule for Safe Flight Over People
The test methods developed at Virginia Tech are the first to be accepted by the FAA to demonstrate compliance with new regulations for a capability critical to the expansion of the drone industry: the ability to fly over people with these planes.
The FAA’s release late last year of a rule for people overflights was a long-awaited indicator of progress in an industry where technological capability has generally exceeded regulatory approvals. Formal acceptance of test methods – known in the industry as a means of compliance – adds practical value to the symbolic meaning of the rule.
“The rule helped understand what is needed to operate over people,” said Tombo Jones, director of the Virginia Tech Mid-Atlantic Aviation Partnership, an FAA-designated drone test site. “But to use the rule, you need a solid process to demonstrate that you meet these requirements. This is what this means of compliance provides, and it will allow drones to be used efficiently and safely for a wider range of operations.
It also strengthens Virginia Tech’s position at the forefront of drone integration, as the industry’s regulatory paradigm shifts to allow flights to become more routine.
This work is the latest victory in a long-standing collaboration between the test site, known as MAAP, and injury biomechanics experts from the Department of Biomedical Engineering and Mechanics. The two nationally recognized groups decided to pool their expertise to study the risks of drone-human impacts shortly after the FAA released its first set of commercial drone rules in 2016 – regulations that banned explicitly overflights of people.
The ban has been a constant sticking point for the industry, as having to avoid hovering over someone on the ground is a significant handicap for many applications otherwise ideal for small drones. (Imagine wedding photography, for example, or delivery operations in urban areas.) It’s also a crucial part of flying beyond visual line of sight, another industry goal: if you can’t see the drone anymore, you can’t guarantee it aren’t there people below.
The FAA granted waivers to this provision when an operator made a convincing case that their planned flights were low risk. These waivers allowed the industry to grow – and, most importantly, spurred the search for effective testing methods – but each waiver only applied to a narrow set of circumstances. Each new type of transaction required a separate waiver.
The new rule swept away much of the red tape that characterized the waiver system by establishing a clear and universal standard related to the severity of the injury. If a drone clearly did not cause injury above a certain level, it could fly over people. (There are still limitations associated with hovering over large groups.)
“Transitioning from operating through waivers to operating under rule means you no longer have to ask the FAA about the safety of each operation on a case-by-case basis,” Jones said. “This makes the evolution towards more ambitious operations considerably more efficient. It also reduces the business risk for drone manufacturers: having a clear standard provides some assurance that there is a well-defined path to be able to operate. “
The FAA released a way to comply with the rule: a simple formula that used the mass and speed of a drone to calculate the total kinetic energy that the plane could transfer to a person during an impact – a metric correlated with the severity of a potential injury.
MAAP chief engineer Robert Briggs said the formula can establish an upper limit of risk without having to perform testing, but the underlying assumptions it uses also prevent most drones from meeting the standard. .
“This assumption is that your drone acts like a rigid object – that when it hits a person, there is no frangibility, no distortion, no complex dynamics. For some drones, this can be a valid assumption, but for many of them it is not, ”he said.
During a real impact, a drone can warp, crack, or even break completely. These structural weaknesses are often built into the design because they dissipate some of the kinetic energy that would otherwise be transferred to whatever the plane strikes.
This wasted kinetic energy provides the latitude most commercial drones will need to meet the standard set by the rule. Virginia Tech’s test methods demonstrate how much energy a particular drone is likely to transfer under realistic conditions, and how that compares to a rigid object with a specified kinetic energy threshold.
These methods have built on years of work by MAAP and the Injury Biomechanics Research Group led by Steve Rowson, associate professor of biomedical engineering and mechanics at Virginia Tech. The partnership espoused MAAP’s experience in assessing risk in drone operations, which provided extensive data on how and why an impact could occur, and the much-loved techniques Rowson and his colleagues used to recreate. laboratory impacts and correlate impact characteristics with the risk of injury. The merger of their expertise has enabled significant achievements, in particular the first national exemption for drone operations on people and the first certification of drone air carrier.
Means of compliance extend the highly specialized tests required for specific exemptions to robust and generalizable procedures that can be applied to a range of aircraft and a variety of operations.
Now that it’s accepted, Virginia Tech can work with applicants such as drone manufacturers to design and test for individual aircraft models. The candidate will submit the test data to the FAA as part of a declaration of compliance with the new rule. In the process, testing will continue to elucidate what it takes to safely fly over people.
“We’re really approaching this as a learning exercise,” Briggs said. “As we begin to perform these tests with various companies, we will learn a lot about the potential severity of injuries from small drones, including how they evolve based on size and design. “
Ultimately, this information will lead to safer operational and aircraft design practices and help guide evidence-based regulation.
“The MAAP exists to inform regulation,” Briggs said. “One of our main goals is to inform the regulations that will create a safer national airspace – and that includes people on the ground.”