17–21 June 2019
Hilton Anatole, Dallas, Texas

Toward “a beautiful web of airplanes”

Posted: 1 May 2017

It would be hard to find anyone who has done more to begin integrating unmanned aircraft into the U.S. national airspace than Dallas Brooks. After an Air Force career that included a stint as the chief of unmanned aircraft systems integration policy, Brooks led a Pentagon task force that worked to ease restrictions on military UAS flights in the U.S. He’s now director of Raspet Flight Research Laboratory, which specializes in unmanned and conventionally piloted flight testing and is an FAA UAS test site. Debra Werner spoke with Brooks about the challenge of integrating a wide range of UAS, from hand-launched 1.9 kilogram Ravens to 2,200 kilogram military Reapers, into U.S. airspace.

Q: How do you get your arms around a problem as large as integration of UAS of all sizes in the national airspace?
Introducing a new technology like UAS into an airspace system that has been predicated on a human pilot being in a cockpit for 100-plus years is a huge challenge. Virtually all of today’s flight regulations levy the ultimate responsibility for safe flight upon that human pilot in the cockpit. In the case of UAS, that paradigm is turned on its head. The cockpit is no longer in the airplane and the pilot no longer directly sees out of the window. So we have to look at how we allocate duties and responsibilities in a way that keeps the rules appropriate and enforceable without necessarily reinventing everything.

Beyond the technical and regulatory integration challenges, there are some cultural and human challenges as well. When you are not sitting in the cockpit, are you as cognizant of the dangers? Are you as alert as you might otherwise be?
It is an extraordinarily large and complex problem set. Trying to treat it like a single problem is usually the way that you fail.

Q: How do you succeed?
One of the most successful approaches is to eat away at it a bite at a time. Divide it into component problems and determine what is achievable today in terms of finding compromises between current regulation, advanced aviation technology and new processes or procedures. To do that effectively, you have to truly understand the processes that drove the original regulations. Only then can we effectively look at how we can either modify UAS to meet those concepts or, when UAS can’t be modified and there is substantial public benefit, then potentially look at revising some of those regulations to allow for those benefits to be realized. Not just because it’s a UAS, but because the public truly sees a value and is rewarded by the operation of the UAS.

Q: What is that value?
There are so many aspects of unmanned systems that are tremendously beneficial. In some respects, UAS represent the future of aviation. UAS can put sensors in the air to accomplish scientific research, everything from analyzing crops to monitoring the environment to finding and repairing power line or pipeline problems. Because they can stay in the air far longer than a human pilot, UAS can search for lost people, track environmental disasters, or help contain extremely hazardous situations, such as radiation leaks. The benefits are tremendous, and that’s before you even begin to assess the potential economic benefits.

Q: What are the component problems that need to be tackled?
Probably the most important one is the reliability of the system. Since there is no human pilot in the cockpit, the UAS has to be absolutely, fundamentally reliable to do what you expect it to do in the event of some malfunction or other off-nominal event. While we do our best as a government to regulate the design and construction of the systems that go into an aircraft, at the end of the day if the system breaks down and other systems break down, the fallback is the pilot’s judgment and the pilot’s actions. If everything else fails and your cockpit goes dark, and you cannot reach air traffic control, that human pilot takes over and uses his best judgment to navigate his way to a safe outcome. When you have an unmanned system in the air, and those same systems sometimes fail, even if they are built to the same level of reliability, then what happens? We can build aircraft to take over for the pilot and do very reliable things, such as auto-divert and auto-land, but our air traffic system must be set up to accept that.

Q: If the command link is lost, what do the UAS do?
One of the benefits of UAS is that should the aircraft lose contact with its control station, it does exactly what it is programmed to do. Human pilots don’t always do that. In some cases, that programming is simple, in other cases, it can be very complex. The Air Force’s Global Hawk is capable of executing a “decision tree” depending on a variety of factors such as location, altitude, et cetera. These contingency options might in some cases provide a divert path to an alternate airport, where the aircraft would automatically fly the published approach and land. Another option might be to alter course to a more remote location, away from other aircraft. But to execute such options safely and without disruption, our air traffic management system, including the pilots of other aircraft, must understand what to expect as well as the UAS pilot does. We’re not there yet, but we’re getting closer.

Q: What were the challenges the military faced in integrating UAS with its fleet?
The fundamental challenges of integrating UAS are the same for both civil and military aviation, but the environments are different. When the military is overseas, prosecuting a particular mission objective, it generally controls the airspace it operates in. That’s a tremendous advantage that allowed our military to mix manned and unmanned aircraft in the same airspace by designing procedures and ensuring everyone followed the rules. It worked very well. Here in the U.S., however, we have a very free and open air traffic system. The military is just one user among thousands, and shares our national airspace with airlines, air cargo, general aviation, other government users, et cetera. Providing for that level of freedom in our U.S.-based system and being able to accommodate that presented a new challenge for the military.

Q: How did the military resolve those challenges?
Again, by breaking the problems down into components that we could solve one piece at a time. One of the things we learned early is when you try to treat all UASs the same, you can almost never get to a perfect solution. Once we started classifying UAS, taking large groups of systems that had common characteristics and solving problems for that group, we began to be successful.

A great example is how we [in the Defense Department] partnered with the FAA to allow for smaller UAS to fly in low-risk environments. We worked out procedures and best practices that allowed the military to fly those smaller and lighter aircraft at lower altitudes with a minimum of restriction. We put those procedures in-place under a memorandum of agreement between the DOD and the FAA in 2007, and they were tremendously successful. Most of what you see in part 107 [of the FAA rules for hobbyists and other small UAS operators], you can trace back to that original 2007 memorandum. They are not completely aligned, but they are close.

Q: What are the differences between military and non-military UAS operations?
In some cases, the military enjoys more capability than the broader public, but there are some good reasons for that. Military UAS operators go through structured, rigorous and defined training programs tailored specifically for the UAS that they are going to fly. A US Army Shadow pilot undergoes months of training specifically to fly the Shadow. They know their aircraft inside and out. But even with all this training, when they graduate they don’t just go fly. They are assigned to a unit with more seasoned pilots, where they build experience in a variety of environments and situations.

In the civilian world, there isn’t that level of standardization. The FAA has to assume a much greater variation in levels of training and experience, and thus a greater margin of safety. In some cases, that means more restrictive limits on when and where you can fly.

Q: What did the Defense Department want from the FAA?
We wanted to be able to fly UAS at military bases across the country so that we could train and qualify our UAS pilots to go overseas. At the time, the FAA had only one mechanism to authorize flights for something that is non-standard in the national airspace. It’s called a Certificate of Waiver or Authorization, a COA for short. COAs are used for a lot of things. For example, if you are having an air show, you are going to have airplanes that are flying too fast for that altitude or extraordinarily low or too close together. The FAA has to specifically approve that by reviewing your plan and procedures to make sure the public isn’t placed at risk. That process posed some challenges for us. We wanted to train and fly routinely. The FAA said, “We need to know specifically where you are going to be. Draw us that track and let’s talk about the timing. And if something goes wrong with that flight, tell us specifically what will happen and how the UAS will respond.” Looking back, those are the specific things that UAS do well, but the military was still developing our procedures, and we weren’t used to being limited like that. We wanted the FAA to trust that we would operate safely and they wanted to know a lot more about how we were operating because this was a new frontier for them. In effect, it became something of a cultural and control battle until we began to build that trust on both sides. That lasted for a few years.

Q: How was that resolved?
In the end, as always happens, people develop relationships and start to build trust based on small victories where they can find common ground. There were people in the DOD who made a concerted effort to invite FAA people to see UAS operations so they could get comfortable with the level of professionalism. Then, the FAA began to open their doors a little bit more and ask us, “How can we approve UAS operations?” That trust built slowly throughout the mid-2000s. Probably the most seminal event that changed the course of UAS integration for the better was when Jim Williams stepped into the job of FAA UAS Integration Office manager.

Q: Why did that make a difference?
He was the right man at the right time. He wanted to make it work. He changed the tone of the narrative and the speed with which decisions were made. Jim built trust by talking directly with people that needed the change, going back, looking hard at FAA processes. When he started to work his magic on that side, a lot of people in the DOD took notice.

Q: How does the FAA’s Next Generation Air Traffic Control System help or hinder UAS integration?
The devil is in the details with NextGen. I maintained in 2005, when NextGen was still being formed, that if you designed the system around the most highly-automated aircraft — unmanned systems — that would unlock the highest efficiency. From there, you can back down the technology to accommodate less automated, less capable aircraft. But if you designed the system fundamentally around the same stick and rudder stuff that we’ve been doing for years, then it’s going to be very tough to integrate new technologies. That argument fell on deaf ears for a number of years.

Q: Why would that approach make sense?
If you design the system to accept an aircraft that will take off, climb, level off, compute the most effective route corrections, negotiate those corrections directly with the air traffic system, make it all the way to its destination and taxi to its hangar, all with literally not a single radio call, then you’ve optimized what the air traffic system is capable of doing.

Q: That would all be done by transferring data?
Yes. When you think of what NextGen was going to provide, it was going to automate systems, and provide more efficient routing. Every aircraft, as opposed to following our current system of “roads in the sky,” would compute the most efficient route. The computers that run the system would de-conflict by time, altitude or other means to ensure that two aircraft would never cross the same place at the same time. We have that kind of computing power and reliability today. Quite frankly, the least reliable piece of that equation is the human pilot. Their skill levels vary. But with an automated system talking to an automated system in a way that both tie in directly and can adjust to each other, the efficiency goes through the ceiling. It becomes a beautiful interconnected web of airplanes going where they need to go when they need to go there.

Q: What insights are you drawing from the ASSURE research initiative?
The research being done by ASSURE is addressing the most critical questions that must be answered if we are to truly integrate UAS into the NAS. One example is assessing the severity of an impact between a UAS and a manned aircraft. For years, we assumed if there’s an impact, it would automatically be assumed as catastrophic. If a UAS hits an airplane, we are going to assume that airplane is going to crash, period. That assumption makes it very tough for any UAS to pass certain safety thresholds for operating in dense flight environments.
But we know that a collision between a UAS and a manned aircraft isn’t necessarily catastrophic — partially because it’s happened. There was an incident overseas where a RQ-7 Shadow hit a C-130 and the C-130 landed safely. The Shadow is a 375-pound [170 kilogram] airplane, not a small UAS, so that was a serious incident — but it wasn’t catastrophic. The question is, when does it become catastrophic? Under what conditions? What size or weight, what density, what relative airspeed, what angle of collision? We’ve never had the data, because true impact testing has never been done. While it’s was pretty easy to assume that below a certain weight or density the UAS might scratch the airplane or chop the propeller a little bit but the airplane is going to be okay, but we don’t know for sure until we test it exhaustively.

Q: How do you gather that data? Do you crash UAS?
In some cases yes, but not with airplanes flying in the sky. We’re doing extensive 3D modeling, and following that up with actual test-firing of UAS components at various aircraft components to verify that our models are accurate. As you might expect, it’s not the small plastic parts on the outside of a UAS that cause the damage. It’s the dense pieces like the motor or the battery. As part of our research scheme, we are firing UAS motors and batteries into aircraft components like wing skins and engines to see what damage they might do. At what level of penetration would the skin begin to separate or rupture? At what velocities? At what densities? At what angles?

We’re doing similar work to assess how harmful a UAS can be if it impacts a person on the ground. That’s a very different thing, and the safety thresholds must be much, much higher. The UAS must be relatively small, slow, and light to ensure they won’t harm an unprotected person. We’re evaluating just how small, slow and light is enough.

Q: What is the status of detect and avoid technology?
It depends. Detect and avoid is a very broad topic, incorporating many different technologies in different ways to achieve a safe result. There are many, many people and organizations working various aspects of this problem. The detect and avoid challenge for a Global Hawk is vastly different than it is for a smaller UAS. [A Global Hawk] climbs through all the altitudes that are used regularly by manned aircraft up to 60,000 feet, where it files virtually alone. When it comes down again, it has to go through that same traffic. So the detect and avoid problem is focused on avoiding manned aircraft that are largely operating according to well-established rules, and around very specific locations. That allows them to optimize a system that is designed and deployed for that environment.
A small UAS is very different. While the Global Hawk would be flying through aircraft that may largely be flying on established airways or identifying themselves by transponder or ADS-B [automatic dependent surveillance-broadcast transmissions], below 500 feet you have none of that. That low altitude airspace is its own aviation culture, with a very different set of rules. There are emergency helicopters, agriculture sprayers, ranchers counting cattle, dozens of very specific applications. Each of those aviation communities have over the years built a network of communications and procedures that are somewhat informal, but they work very well. But if you begin to introduce what may become hundreds of thousands of unmanned aircraft into that low-altitude arena, that can be very disruptive. The existing tools to mitigate the resultant safety gap are currently very limited. Air traffic control radar doesn’t go that low. Generally, air traffic control doesn’t even talk to aircraft operating that low. So that puts a great deal of responsibility on the UAS to ensure it stays well clear of every other aircraft out there.

Q: How is the Science and Research Panel for Unmanned Aircraft Systems addressing these issues?
The SARP has taken an important first step in the detect and avoid equation by determining how close is close enough. We call that “well clear” in aviation parlance. The regulation says that you have to pass “well clear” of other aircraft, but “well clear” has never been assigned a specific number — it’s largely been a subjective judgement of a human pilot. Unmanned aircraft systems don’t have eyeballs looking out of a cockpit saying, “That’s probably close enough.” They have to measure accurately, with radar or laser or optical instruments. The SARP has done the research to help define what that number should be for large UAS. Now we’ve turned our attention to helping define it for small UAS.

Q: What are those numbers?
For large UAS, we took into consideration that there is a minimum distance we want to achieve, but that distance isn’t the only factor. That distance changes dramatically depending on how fast the two aircraft are closing in. In those situations, it’s more about time than distance. Two helicopters that are closing together at a combined speed of 20 miles an hour [32 kph] have a lot of time to get out of the way. Two jets closing at 400 miles an hour [644 kph] have very little time to get out of the way. So, we define that equation in terms of time, with a minimum distance to make sure.
For large UAS operating in proximity to manned aircraft, the SARP recommended that the time to the closest point of approach could not be less than 35 seconds.  Having that threshold allows us to work backward and calculate when an avoidance maneuver has to be executed to ensure the two aircraft pass well clear. But even with time built into the equation, we recognized that two aircraft should always stay a minimum distance apart. Regardless of the speed and regardless of the time, we determined that the larger UAS should pass no closer than 4,000 feet horizontally from another aircraft. Vertically, we said set an alert threshold of 700 feet, with a minimum separation threshold of 450 feet. This aligns with the FAA’s commonly accepted standards for vertical separation in the visual flight rules environment.

Q: Will those separation rules go into effect?
They are not rules, or even recommended rules. They are designed to be scientifically based, highly-modeled and extensively validated inputs that help support broader FAA considerations in aviation rulemaking. These numbers don’t exist in a vacuum. There are many, many more factors that must be considered before you arrive at a new potential rule and the FAA is well-versed in how to do that. The SARP is not the FAA, or even an arm of the FAA. We provided our recommendations, based on hundreds of thousands of simulations, to the Radio Technical Commission for Aeronautics Special Committee 228, which governs unmanned aircraft systems integration. RTCA then incorporated those recommendations into their minimum operation performance standards for UAS. Those go to the FAA for review and potential adoption as they see fit.


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