The persistent divide between advocates and skeptics of unmanned aircraft systems (UASs) being integrated safely into the U.S. National Airspace System (NAS) shows signs of narrowing, according to speakers at two recent industry events. Open-ended speculation, criticism and resistance appear to be yielding to an urgent need for cooperation among stakeholders to mitigate risks implicit in the federally mandated UAS integration process set in motion in early 2012 (ASW, 3/12, p. 34). Presenters typically described UAS integration a vital common interest.
The views were shared at the 2012 ALPA Air Safety Forum conducted in Washington by the Air Line Pilots Association, International (ALPA) and at ISASI 2012, a seminar conducted in Baltimore by the International Society of Air Safety Investigators (ISASI).
“The amount of time already elapsed in bringing forth civil, certified, routine [UAS] operations has frustrated many proponents and advocates, and has resulted in lobbying and political pressure,” said Ellis Chernoff, a FedEx Express captain and the ALPA UAS Team lead. “Committee deadlines and legislative mandates have been the obvious response. But there can be no shortcut to safety, and we have a responsibility to our pilot membership and to the public we serve to hold fast to the highest standards of safety and to get the details right.”
He was referring to the U.S. Federal Aviation Administration (FAA) Modernization and Reform Act of 2012 — containing provisions for the safe integration of UASs into the NAS no later than Sept. 30, 2015 — that was signed into law in February.
“In manned aviation, it’s expected that pilots see and avoid traffic and other hazards,” said Bill de Groh, an American Eagle Airlines captain and chairman, ALPA Aircraft Design and Operations Group. “A new concept is introduced [for UASs], called sense-and-avoid, and attempts to close this gap. … UAs must be compatible with TCAS [traffic-alert and collision avoidance system]–equipped aircraft but also remain safely separated from all air traffic. ADS-B In [automatic dependent surveillance–broadcast] may eventually offer a possible solution to this issue” (see “Sense-and-Avoid Update.”). The FAA defines sense-and-avoid as “the capability of a UAS to remain well clear from and avoid collisions with other airborne traffic.”
Sense-and-Avoid Research Update
U.S. researchers in September observed the performance of two mature sense-and-avoid algorithms for unmanned aircraft systems (UASs) during a series of flight tests near Grand Forks, North Dakota. Flights comprised 120 encounters in which automatic maneuvers by a UA-surrogate airplane were expected to resolve virtual traffic conflicts with an intruder aircraft, participants said. A major purpose of the two weeks of flights was to compile data for later validation of sense-and-avoid computer simulations.
Complete results await final reports, but examples of successful conflict-avoidance maneuvers were replayed for AeroSafety World and other media representatives in a Web conference–based telephone briefing about the Limited Deployment–Cooperative Airspace Project (LD–CAP). The briefing was led by representatives of the U.S. National Aeronautics and Space Administration (NASA) Langley Research Center, MITRE Corp. and the University of North Dakota (UND) on behalf of all the research partners.1 LD-CAP, now midway through its two-year research agenda, plans to share results with the aviation research community and regulators, they said.
“What we want to do is create the scientific data that the community needs to make decisions about how to mitigate [UASs’] lack of see-and-avoid with a sense-and-avoid solution [for routine flight in non-segregated civil airspace],” said Andy Lacher, MITRE’s UAS integration lead. “We’re using the [flight] data to validate our computer models and inform the community about the performance and the viability of a cooperative, autonomous, sense-and-avoid algorithm. … We’re conducting this research using a [NASA-owned] surrogate unmanned aircraft — an SR22, it’s a Cirrus aircraft. … The sensor we are focused on in this research is … automatic dependent surveillance–broadcast [ADS-B]. … We don’t necessarily believe [ADS-B] is the sole sensor that would be appropriate for sense-and-avoid, but it is a good sensor to evaluate because of its excellent accuracy. It’s a good sensor source to be used for determining whether you can have an automatic algorithm.
“We are focusing on conflict avoidance under visual flight rules in … airspace where aircraft [pilots] may not be receiving ATC [air traffic control] separation services. … We’re looking at conflict avoidance, keeping the aircraft well clear of each other [so] as to not present a collision hazard. We are not necessarily focused on collision avoidance, and [there] are some real differences between TCAS [traffic-alert and collision avoidance systems] and the [LD-CAP] activities. … TCAS is an alert to the pilot; it is not an automatic [aircraft/UA] maneuver.”
Each aircraft was equipped with a Garmin GDL 90 ADS-B datalink transceiver with a 978-MHz universal access transceiver [UAT] link. “There is every reason to believe that the algorithms would work with … a UAT [link] or the 1090-MHz extended squitter link,” he said. One algorithm was supplied by MITRE and the other was supplied by UND, each with a series of modifications. RTCA Special Committee 203 and other standards bodies will consider these and other data in producing a set of sense-and-avoid technical standards.
LD-CAP’s agenda covers the development and testing of algorithms that rely on ADS-B; identifying methods of commanding UAS sense-and-avoid maneuvers to avoid conflict with manned aircraft that lack ADS-B; education of the general aviation community about ADS-B benefits in this context; and reducing the size, weight and cost of ADS-B equipment.
The second item on this agenda will consider the feasibility of creating and transmitting alternative messages equivalent to ADS-B messages. Currently, aircraft transponder-reply targets appear on ATC displays in response to secondary-surveillance radar interrogations, and then “aircraft tracks are uplinked to ADS-B-equipped aircraft via TIS-B, traffic information surveillance–broadcast messages,” Lacher said. “But that only applies to aircraft that are transponder-equipped. We’re looking at a capability that will allow aircraft that are only being tracked with primary radar to have TIS-B messages. … That [testing] is planned for spring of 2013.”
The flight data animation replays showed algorithms commanding the autopilot of the SR22 surrogate UA to turn well clear to avoid conflicts with the intruder airplane. UA maneuvers not replayed at the briefing included climbs, descents and speed adjustments for successful avoidance of the intruder, Lacher said.
LD-CAP has addressed both the see/sense-and-avoid and lost-link issues surrounding UAS integration. “That’s a big deal,” said Mark Askelson, associate professor, Department of Atmospheric Sciences, University of North Dakota (UND). “[LD-CAP is] open to testing algorithms from anyone who is ready to do it.” In their work on these algorithms, he noted, UND’s “students have been able to develop a concept and see it to the point of being flight-tested.”
Flight testing essentially helps to assess the sense-and-avoid technology readiness level in winds and atmospheric conditions, said Frank Jones, LD-CAP deployment lead, NASA Langley. Before the flight tests, computer simulations already had analyzed more than 2 million encounters between a virtual UA and a virtual intruder aircraft, he said. During the flight tests, the latest data usually were reintroduced the same day to computer simulations, and the algorithms were modified and uploaded for the next day’s flight tests. MITRE algorithm-evaluator software also generated technical “report card” assessments.
“Essentially, what we have is a general purpose computer [aboard the SR22 UAS surrogate] that interfaces to the autopilot such that we can fly the aircraft [using] a research operator in the back seat of the aircraft,” Jones said. Playing the role of a pilot in a ground control station, the back seat pilot issued commands to the [UAS] autopilot for heading, speed, climb/descent and altitude changes. Rick Yasky, chief pilot, NASA Langley, occupied the front left seat as safety pilot of the SR22 with capability to override the UAS systems and fly the aircraft if required.
Another mitigation of the risk of in-flight collision during these experiments was operation of the Cessna 172 intruder only at real altitudes intentionally biased/offset by 2,000 feet from the altitude of the SR22 UAS surrogate. Data used by the algorithm, however, compensated for the offset. Therefore, the algorithm responded automatically to a “ghost aircraft” — that is, as if the C-172 were a physical intruder closing at the same altitude, overtaking or engaged in another of about 20 conflicting geometries.
What triggered the automatic maneuvers was the algorithm’s protective logic, in which the C-172 was continuously surrounded by protected volume of “no-fly zone” airspace — 500 ft above/below and 2 nm (3.7 km) laterally. The boundaries of this volume also were the procedural intervention point at which the safety pilot in the SR22 surrogate UAS was required to immediately take over the SR22 flight controls. The C-172 pilot similarly was required by procedure to avoid penetration of its protected volume.
In replays of cockpit video, the SR22 pilots monitored the ownship in the center and the relative positions of other aircraft, in part, on a navigation display. As the SR22 UAS surrogate overtakes the ghost C-172 in one encounter, “The [C-172] traffic with yellow highlighting means that the algorithm has triggered, sensing a potential conflict,” said NASA Langley’s Yasky. The pilots saw immediately on a separate display commands and triggers that the algorithm was generating and sending to the autopilot, and the SR22 turned as expected to avoid the conflict.
Testing the algorithms’ ability to automatically and simultaneously avoid conflicts between a UAS and multiple intruder aircraft also will be part of LD-CAP, possibly in June 2013. Lacher noted that the LD-CAP partners have coordinated their work with parallel research under way by others into complex UAS sense-and-avoid technology, sensors and algorithms.
LD-CAP work is one element of UAS integration, and is distinctive in looking at solutions that do not directly address the UAS pilot. “The research we’re focused on [applies] if the [UAS pilots are] unable to execute a maneuver,” MITRE’s Lacher said. “First, you want to provide information to [pilots] to give [them] situational awareness. They may make the decision to maneuver the aircraft before our automatic alert would trigger a maneuver. That would be the preferable mechanism. But …maybe they didn’t receive the [traffic-avoidance] alert for some reason, or maybe the link between the ground control station … and the aircraft is disrupted or interfered with in some way. You want the aircraft to still be able, in a self-contained manner, to maneuver by itself to avoid those collisions. So you might have multiple sensors, some of those sensors feeding data to the pilot on the ground, other sensors feeding data to algorithms … on board the aircraft that would [command an autopilot] maneuver.”
- Other partners are Draper Laboratory, North Dakota National Guard, North Dakota State University and the State of North Dakota.
By mid-2012, the FAA was reorganizing its UAS-related work under the new Unmanned Aircraft Systems Integration Office (AFS-80) within the Flight Standards Service, while addressing the law’s requirements. “We’re not going to do anything that compromises safety when it comes to the integration of unmanned aircraft into the National Airspace System,” said FAA Acting Administrator Michael Huerta. “And in order to do that — what we need to do that — is good, solid data. … Just recently, the FAA received the first application for a type certificate for a commercial unmanned aircraft.” In this context, the FAA has requested and received extensive public input about specific aspects of UAS integration, including the management of six UAS test sites (to be selected by December), training requirements, operator experience, uses of airspace, collecting safety data and coordinating further research and development work.
The U.S. government has had a policy of accommodation of UASs in the NAS, allowing private recreational flights by model aircraft; allowing UA operation without approval only in active restricted areas and warning areas; issuing certificates of authorization or waiver (COAs) only to public use UAs; or issuing special airworthiness certificates in the experimental category and special flight permits for UA flight testing (ASW, 7/08, p. 34).
Under COAs, UAs currently operate in most classes of airspace but flight over populated areas is not approved. The details of integration into the NAS within three years and later into the Next Generation Air Transportation System (NextGen) are still being decided.
The new FAA office focuses on the “safe, efficient and timely” integration of UASs into the NAS, but also recognizes “a little bit of conflict” among these three qualifiers, said Richard Prosek, manager of the UAS Integration Office. “We could perhaps find a way —if somebody wanted to — to fly a [Northrop Grumman RQ-4] Global Hawk from [John F. Kennedy International] Airport [to Chicago O’Hare International Airport] and land on [Runway] 22L,” Prosek said, as an example. “We could find a way to do that safely, but it would come at the expense of the efficiency of [the NAS].” The office operates under the same tenets that the FAA announced in 2007: that UAs are aircraft, and they must be flown by utilizing a pilot-in-command, he added.
An FAA Civil/Public UAS NAS Integration Roadmap mandated by the law is being developed by this office, led by UAS Executive James H. Williams, and the FAA concept of operations is being produced by the FAA NextGen Office. Recommendations from the FAA UAS Aviation Rulemaking Committee, established in June, were to have been incorporated into the comprehensive plan by the end of September, Prosek said. The Joint Planning and Development Office, comprising multiple government-military entities, has responsibility for the comprehensive plan.
In May, a presentation by Williams listed UA reliability, UA certification standards, certification of ground control stations, pilot qualification standards, dedicated protected radio spectrum, sense-and-avoid capability, and NextGen ground system design as critical issues in integration. A notice of proposed rule making is scheduled for release in late 2012 “to enable small [UAs] to operate safely in limited portions of the NAS and gather data.”
Window of Opportunity
From the perspective of UAS manufacturers, integration will have profound societal benefits, including long-term economic competitiveness. “No one in this industry expects that we’re going to wake up [in the United States on Sept. 30,] 2015, and find the skies darkened with unmanned aircraft systems — that’s just not reality,” said Paul McDuffee, associate vice president of government relations and strategy, Insitu, a subsidiary of The Boeing Co. “We’re going to start operating systems where it makes sense to operate them. We are not going to push the envelope beyond our capabilities. … We are in a situation, though, where the technology appears to have outpaced the regulatory environment, and as a result of that, there are a number of misconceptions about what UASs are and what UASs are not. … It’s clear UASs are here to stay — it’s a technology that has tremendous value.”
One competitive challenge appeared in his estimate that more than 1,000 manufacturers of UASs now exist worldwide. Another is that operators of manned aircraft and unmanned aircraft in coming decades will begin to compete in a multibillion-dollar industry, he said.
“One of the things that we face every day is the misconception that UASs are an inexpensive alternative to a manned aircraft–type of deployment,” McDuffee said. “At this point in time, nothing could be further from the truth. Until routine access to airspace, and routine and regular use of UASs occurs, we’re looking at a situation where the economics may not be what everyone anticipates.”
UA Pilot Perspective
From the vantage point of military pilots flying the largest UAs, called Group 4 and Group 5, these aircraft are the closest to readiness for integration. “Potentially, [they] can operate in the vast majority of the airspace that [airline pilots] will operate [in],” said U.S. Air Force Col. Carl King, remotely piloted aircraft liaison for the U.S. Department of Defense to the FAA. “I’m not going to suggest that we share it, but those are the systems that we train our operators to fly, basically, in all classes of airspace as we get there.”
These pilots complete essentially the same undergraduate pilot training program as pilots of military manned aircraft, including the military counterpart of an instrument rating and 200 hours of simulator training. “Then [the UA pilots] go off and they focus on their systems,” he said.
Inside the ground control station for a typical UA from these groups, a green line on a navigation display shows the programmed route of flight and, when the pilot activates the autopilot, the UA follows that route of flight. A red line simultaneously indicates the programmed route of flight “if the aircraft were to go ‘lost link’ [which] gives me a constant update as to where it’s going to go,” he said.
During military UA pilots’ routine practice of manual flight, such as touch-and-go landings in an airport traffic pattern or instrument approaches to an airport or runway end, the pilot selects an overlay of the traffic pattern map or approach chart on the navigation display to fly along a black line while checking ground references displayed from on-board video cameras.
Pilots of these military UAs typically operate with extensive real-time data from the ground, King said. “Once we get going, we have it all [information such as mission updates, traffic deconfliction and selectable global weather maps] instantly.” Secure, high-bandwidth Internet links facilitate near real-time worldwide communication with controlling agencies and air traffic control (ATC), he said. Pilots of these UAs also have radio communication with ATC for traffic separation in controlled airspace but not yet a safe replacement for human see-and-avoid capability. Currently, multiple sensor systems depict traffic to the UA pilots on their ground control station displays.
“Obviously, sense-and-avoid is a big issue that we have within the aircraft,” King said. “[For now, our] center screen [is] a big blow-up of the world that we are flying in, and that will scale in and out. … We [connect air traffic] data feeds and then we can display each of them. This is not … an ‘I can go anywhere’ kind of system, but this does help us get situational awareness to see where the rest of our aircraft are. We can do some significant deconfliction [but] it is not a sense-and-avoid system quite yet.”
Airline Pilot Concerns
ALPA pilots collectively express a number of safety-related concerns about integration. “Whether unmanned aircraft are ‘accommodated’ or ‘fully integrated’ into the NAS, responsibility for safety remains the same, even though the tasks and details of operations are different,” said ALPA’s Chernoff. “The skies are plenty crowded, and there must be a means to fly the correct altitude, determine legal visibility [and] maintain required cloud clearance and required ground track. This is not a simple matter, and the systems that support this are far more complex than in typical [manned] light aircraft.”
Except for line-of-sight control of the smallest UAs, ALPA argues that UA pilot certification must include an instrument rating. “In unmanned aviation [with the next generation of pilots], the new pilot might start out with advanced systems and displays, and the training and qualification must take that into account,” Chernoff said.
So far, ALPA has not been sold on the efficacy of some proposed sense-and-avoid solutions based on high-resolution surveillance radar on the ground. “It can provide simple intruder alerts allowing limited UAS flight operations in a particular area without creating special-activity airspace — or it can provide some level of conflict resolution for the remote pilot,” he said. “While it might be useful in testing and validating a true airborne collision–avoidance system, it can never be a substitute for one.”
By the time integration materializes, civilian accident investigators will need to be prepared for known forensic challenges (ASW, 12/07, p. 42) and some unique complexities involved in UA crashes and UA-related crashes. Moreover, the profession should have a voice today in the UAS risk mitigations under development to help prevent accidents, some accident investigators said.
Tom Farrier, chairman of ISASI’s UAS Working Group, said that integration steps must fully consider all that will be required for effective accident investigation. “We’re watching the evolution of an industry,” he said, accepting what he called “indisputable” predictions that U.S. civilian uses of UAS will increase along a “very rapidly climbing slope.”
“As the numbers go up, you’re going to have more and more interactions between manned and unmanned aircraft, and we can’t predict how they are going to happen,” Farrier said. Some investigators anticipate that the most probable categories of UAS accidents will be the crash of a manned aircraft as the result of a collision with an unmanned aircraft, and a fatality or a major injury that results directly from unmanned aircraft operations of some type, he said.
Investigators lack data for UAS events equivalent to that in the Boeing Statistical Summary of Commercial Jet Airplane Accidents, he said, and this lack of data impedes their prioritization of risk reductions. “There simply is not enough data,” Farrier said. “Some of the … military services have some of that kind of information, but they don’t want to give it to us.”
An aspect of UAS accidents that remains a gray area is when to conduct an investigation in light of economically strained investigative resources. Perhaps the first criterion should be, “What kind of events should we be worried about that might have had a hazardous outcome under other circumstances?” he said. “In other words, the chain of causality got broken in some way.” A second high-priority concern should be any increased volume of such events and the possibility that one of these could occur at a particularly inopportune time, he said. Without regulatory criteria mandating such investigations, people will have to substitute personal judgment calls — perhaps deciding to investigate solely because of the potentially valuable lessons to be learned, regardless of UA size/weight, he said.
“Some of the decision making is going to be very situational, but at least you can do some advance thinking about it,” Farrier said, noting that some future interactions already are predictable. “[What] if law enforcement is out there with a manned aircraft and electronic news gathering organizations are out there with unmanned aircraft chasing the manned aircraft? You could very easily foresee some serious kinds of problems with these kinds of interactions.”
Investigators also must be alert for causal factors such as component reliability when identical or nearly identical engines or other parts are common to both UA fleets and manned-aircraft fleets, so that all stakeholders can be alerted to findings and safety recommendations, he added.
He shared ALPA’s skepticism about the likelihood of large-scale systemic changes being accomplished to make feasible safe sense-and-avoid solutions for active and passive targets. “As a practical matter [and] as somebody who has been watching this field for a number of years now, you’re never going to make something like that small enough to fit on at least 90 percent of the airplanes that are going to be up there,” Farrier said.
UAS architectures can be more complex in their possible points of failure (Figure 1) than generic diagrams indicate, he said. One example is a UA that only operates autonomously on a brief, temporary basis — in some cases, after the pilot has been following the flight path by pilotage, comparing the on-board camera’s terrain imagery to a surface map displayed inside the UAS ground station — and outside the visual range of the pilot.
“There have been a number of losses of aircraft being operated in just this manner where it seems pretty obvious that the [UA] had just flown too far away to ‘hear’ its ground control station,” Farrier said. “Quite a few of them don’t seem to [enable the pilot to recapture the UA]. Perhaps their lost-link profile brings them in contact with some kind of surface feature before they can get back in the link. Maybe they are just failing to respond to on-board programming [and] when it’s actually put to the real test, it doesn’t work. We call those fly-aways. I think there are a lot of fly-aways. … So we need to document these kinds of events, and in some cases, it may be prudent to expend some investigative resources just to develop an idea of whether this is a pattern within a given operator or operation.”
The ISASI UAS Working Group has begun to develop a description of UASs generic enough to accommodate the entire spectrum of investigations. The description is expected to be helpful in directing specific investigative tasks. “The no. 1 thing that I think you can bear in mind is … if it’s an aircraft, it’s going to crash like an aircraft. … With the unmanned aircraft, you are going to have the added question of, ‘Was the link between the pilot-in-command and the aircraft intact or not?’” Farrier said. “And that becomes a lot more difficult task to accomplish because, in part, not too many people in our profession really are familiar with how the electromagnetic spectrum works [for UASs], and how the different protocols, developed for passing along commands, are being processed aboard the [UA].”