Europe’s experience of operating unmanned air vehicles (UAVs) within its controlled airspace is considerable. Predators, Hunters and other UAVs operating during the conflicts in Kosovo and Bosnia, for example, were successfully sequenced amidst commercial and military traffic.
"We had Predators flying all over the Balkans, and we complied with all the rules and regulations just like a manned airplane," comments Tom Cassidy, president of General Atomics Aeronautical Systems, producer of the propeller-driven Predator. UAV controllers (pilots) communicated with air traffic controllers as if they were on the aircraft, and even made ILS approaches at military airfields.
UAV operators say it was easier to see and avoid other traffic than it was for them to convince the air traffic authorities that they could do so. However, some industry observers point out that accommodating UAVs was "no cakewalk." For instance, greater separations had to be allowed around UAVs because of their relatively imprecise altimeters and other sensors. Procedures had to be adapted literally "on the fly" during the Balkans conflicts, and some civil traffic had to be curtailed or rerouted because of UAV operations. Only the exigencies of war make such an approach tolerable.
Organizations ranging from NATO to national civil aviation authorities (CAAs) recognize that much more work must be done to integrate UAVs with manned aircraft. Unmanned air vehicles will require sophisticated control systems with appropriate levels of autonomy, effective sense-and-avoid mechanisms, and high-integrity data links. These will be needed, in part, because neither military nor civil UAV operators will be happy to see their aircraft limited to special-use airspace or to have long-range platforms like Global Hawk and the proposed Euro Hawk be limited to cruise altitudes above 50,000 feet and to spiral climb and descent patterns.
German Research
The German aerospace research organization, Deutsche Zentrum fur Luft und Raumfahrt (DLR), heads one national initiative tackling the airspace integration issue. It aims to develop viable air traffic control (ATC) procedures and determine desirable characteristics for future survivable air-ground data links. Collaborating with European Aeronautic Defense and Space Co. (EADS) and the electronics company, ESG, DLR is conducting a series of trials with its VFW614 Advanced Technologies Testing Aircraft System (ATTAS). Equipped with UAV avionics, this light jet has a test pilot on board who, once the aircraft is airborne, normally relinquishes control to automatic systems. The experimental testbed is flown in and out of various categories of airspace under instrument flight rules (IFR). Meanwhile, air traffic controllers are determining how much existing procedures, such as handovers between ATC centers and deconflicting routines, will need to be modified to accommodate unmanned aircraft.
Rather than tie up live equipment, the controllers also use an ATC simulator. DLR and EADS Military Aircraft have made this part of a more comprehensive synthetic environment, which also includes a high-altitude/low-endurance (HALE) UAV simulator. The latter extends the range of aircraft maneuver capability beyond the envelope of the VFW614, for instance, with higher turn and climb rates. The HALE simulator also permits scenarios that could not safely be created using manned aircraft, such as complete loss of engine power.
Ultimately, controllers want to process UAVs through their sectors by relaying guidance commands in real time via data link–much like processing manned aircraft operating in IFR airspace. EADS is focusing particularly on the safe return of UAVs following a data link failure. Because hostile jamming, tactical maneuvering or other issues can compromise data link continuity, UAVs will "have to be able to manage by themselves," says an EADS official. This means flying to the UAV’s home base or diverting to a nearby airfield while avoiding controlled airspace in the process.
Officials at Sweden’s Saab, applying experience from developing the Gripen manned combat aircraft to the flight control of UAVs, agree. Hans Berglund, deputy program director-UAV systems, is clear that, to allow unmanned vehicles to fly outside the country’s extensive military ranges, they must be "as safe as any other aircraft." He suggests that the accident probability for unmanned air vehicles must lie between that of a fighter aircraft and a civil air transport.
For UAVs to share airspace with manned aircraft, civil and military authorities in Europe, the United States, Japan and Australia have launched UAV certification initiatives. One of the first was the complex certification of the Royal Netherlands Army’s Sperwer UAV system. But some European officials believe individual initiatives are of dubious value in the absence of an internationally accepted roadmap governing airworthiness and certification issues. Says one spokesman, "Because airspace has become a global concern, we have to move ahead together on a consensual basis."
Universality is the aim of the European Unmanned Vehicle Systems Association (Euro UVS) and its president, Peter van Blyenburgh. Euro UVS is funded by its members–98 corporate, academic and institutional organizations in 23 countries and 64 honorary members in 17 countries worldwide. According to van Blyenburgh, international agreement is needed on such basics as the terminology surrounding UAVs before even starting to think about common codes and practices. In defining thousands of technical terms, Euro UVS working parties have wrestled with such questions as:
What constitutes a control station, since this can be on the ground or in the air?
Whether the person who guides the UAV is a pilot or an operator?
Whether data link should be considered as two entities, one for control and the other for information? And, reaching right to the heart of the matter,
What precisely a UAV is? (Various other acronyms have been used, as well as different definitions for UAV, such as "uninhabited" air vehicle.)
UAV Classification
Another basic preoccupation has been the classification of UAVs. European countries have agreed that this should be done on the basis of a platform’s mass and speed, i.e., kinetic energy. Categories would range from "enlarged model aircraft" on line-of-sight control at low levels, which could be exempt from ATM regulation, to large HALE types such as Global Hawk, which may require full ATM compatibility.
Euro UVS works closely with the U.S. Association for Unmanned Vehicle Systems International (AUVSI) and has won a number of airspace-associated study contracts. In November 2000 the French civil aviation authority–the Direction Generale de l’Aviation Civile (DGAC)–asked Euro UVS to study Europe’s certification and ATM policy and procedures as they apply to UAVs. The association subcontracted three companies to evaluate existing joint airworthiness requirements (JARs): Dassault Aviation to study JAR 23 (normal, utility, aerobatic and commuter aircraft), SAGEM to evaluate JAR-VLA (for very light aircraft), and Thales Airborne Systems to examine JAR-VLR (for rotary-wing aircraft). Their results have been posted on www.ucare-network.org.
The French Ministry of Defense also has asked EuroUVS to lead a collaboration of European UAV working groups in the UK, Spain, Austria, Germany and Switzerland, as well as France. Working within a military context, the collaboration was tasked to:
Categorize current and planned UAV missions,
Define UAV categories established for certification standards,
Recommend standards and methods for UAV operations, and
Examine existing certification procedures.
The French MoD also asked for recommendations on the certification of UAV equipment, such as situational awareness sensors and computer technology on which to base ground control stations, communication links, navigation systems and "pilot substitutes" (augmented automatic flight control systems). It also sought tools for establishing the operational viability of UAV systems and subsystems, including degraded modes. This study is virtually complete; its results are due imminently.
NATO also selected Euro UVS to contribute to a study that would highlight the technologies needed to realize fully autonomous UAVs. These vehicles, which are preprogrammed for given missions and require no piloting, would need a high level of sense-and-avoid capability, probably using artificial intelligence.
In addition, to unite the worldwide UAV community behind a common goal, Euro UVS has initiated the international UCARE (UAVs: Concerted Actions for required REgulations) program to facilitate the framing of rules and regulations governing UAVs’ integration into managed airspace. The multinational network was tasked to:
Incorporate the findings of national working groups,
Present the views of UAV stakeholders financing their own activities, and
Make documents and opinion papers available to the entire UAV community.
UCARE has three permanent working groups, covering integration, airworthiness and certification, and operations. Eurocontrol, FAA, NATO, the Joint Airworthiness Authority (JAA) and national CAAs can ask UCARE to take on related projects.
Finally, Euro UVS is a participant in a JAA/Eurocontrol UAV Task Force, which is due to report in September the results of a comprehensive study that covers UAV_design, production, certification, maintenance and operations. The task force’s terms of reference, aired at the UAV2002 conference held in Paris in June 2002, include:
Identification of current and developing UAV technologies and their applications,
Creation of UAV categories,
Identification of a lower mass limit (regarding UAVs small enough not to require air traffic management) for regulation at the European level,
Review of existing research studies, draft standards and other publications, and
Promotion of a total-system approach.
Aspects under study include terminology, legal issues, operator training and qualification, and areas of conflict and deconfliction. They also include control procedures for all phases of flight–from taxi, takeoff, climb, cruise and task execution to descent, approach and landing–under normal and failure cases.
A preliminary study report issued last year concluded that, wherever possible, UAVs should conform to existing procedures, regulations and requirements, rather than involve infrastructural adjustments. In many cases this would necessitate carrying the same navigation, flight control system, transponder and other equipment that are fitted in manned aircraft, albeit in forms engineered for lower weight and footprint.
Criticality of Data Links
Probably the most pressing requirement is a system of secure, high-integrity data links between the unmanned air vehicle, the control station, and the ATC centers, plus a voice link between the UAV controller and air traffic control. The links may be line of sight or extended by satellite or other relay. Onboard video cameras may be needed for remotely piloted landings, while fully autonomous vehicles could require an ILS, microwave landing system (MLS) or transponder landing system. Navigation could be a blend of GPS, differential GPS and inertial nav. Large, HALE-type UAVs probably would have an onboard flight management system that, unlike the FMS in manned aircraft, would be accessible to the ground controller so that routes and waypoints can be updated.
The accuracy of onboard altimetric and other sensors will be defined according to the UAV category and stipulated flight-path accuracy. Emergency flight termination systems may be needed, ranging from parachute landing systems to explosive devices.
To locate and track UAVs on the ground, optical sensors, multilateration or tarmac-embedded induction sensors may be required. And UAV controllers may need improved human/machine interfaces featuring large-screen situational awareness displays and moving maps. They probably will have to file UAV flight plans and listen for ATC calls on emergency frequencies. Much applicable technology exists already in the military domain, says the report, but needs spinning out into the civil arena.
The JAA/Eurocontrol task force will have taken into account work funded by the European Commission under its 5th Framework Program (FP5) for Research and Technology. Projects initiated within the FP5 growth program have included formation of UAVNET, a network of official, commercial and academic interests pursuing civil UAV applications, and CAPECON, which focuses on safe and cost-effective applications of civil UAVs. (The full meaning of the acronym is Civil UAV APplications and Economic effectiveness of potential CONfiguration solutions.) Most pertinent to airspace, however, is the USICO (UAV Safety Issues for Civil Operation) study, aimed at eventually integrating a demonstrator UAV into an ATM environment. One focus for USICO is the critical issue of collision avoidance. According to Andre Clot of UK’s Remote Systems Group, which has participated in a number of studies, CAAs will require UAV systems to demonstrate levels of safety at least equivalent to those of manned flight. (The UK CAA has set the tone with its CAP 722 document, titled "Unmanned Aerial Vehicle Operations in UK Airspace-Guidance.")
Traffic avoidance will require effective onboard sense-and-avoid technologies, typically using optical/infrared, radar or light detection and ranging (LIDAR) sensors. Alternatively, transponder-based systems like identification friend or foe (IFF), traffic alert and collision avoidance system (TCAS) and automatic dependent surveillance-broadcast (ADS-B) could be used. Whatever technology is adopted, it should be equally capable in instrument meteorological conditions (IMC) and visual meteorological conditions (VMC), so that UAVs can coexist with both VFR and IFR traffic.
ADS-B can serve whether the aircraft is on the ground or in the air and can either be integrated with autonomous aircraft systems or provide ground controllers with high situational awareness. Where data transmitted from multiple platforms is fused on the ground for controller use, says Clot, issues of latency (data capture and processing delays), resolution limits and compression loss will require the use of high-bandwidth data links.
Transponders in UAVs have a downside, however. Not all aircraft have transponders or want to advertise their presence, so certain platforms may remain unseen by the system. And today’s transponders are heavy.
While the European Community, JAA and Eurocontrol studies should lead to an initial roadmap for UAVs’ integration into European airspace, their results are just a start. A follow-on study to current JAA/Eurocontrol research already is planned. The onslaught of UAVs has created a sense of urgency. Euro UVS and similar groups believe national aviation authorities must accelerate joint integration processes so that the growing number of UAVs and UAV applications don’t take them by surprise.
Certifying Sperwer
Certification of the Royal Netherlands Army’s Sperwer (meaning sparrow hawk) tactical unmanned air vehicle (UAV) was no small feat. It took five years to accomplish, involving as many political hurdles as technological hurdles. Sperwer is the Dutch Army’s first air vehicle, so the service needed to seek the assistance of the Royal Netherlands Air Force, as well as UAV manufacturer SAGEM SA, to achieve certification.
Essentially, certifying a UAV for civil airspace is comparable to certifying a small manned air vehicle. "You have to take four things into account," says
Jean-Charles Pignot, SAGEM spokesman. They are:
Aircraft certification, which is "a little like certifying a Cessna 172’s airworthiness," according to Pignot. SAGEM had to show specs and their relation to the UAV’s operation.
An operator’s (pilot’s) license, which requires that the person on the ground manning the UAV is trained and qualified. A user’s manual must accompany the aircraft.
Qualified maintenance, to assure the UAV remains airworthy. A maintenance manual also must accompany the aircraft.
And operational rules that allow UAVs to safely mix with manned aircraft.
"The operational aspect of certification can be the big issue," says Pignot. "It’s not a technical problem, but a political problem–a matter of determining what must be done during UAV flight. We can demonstrate any number of things [during certification flight]," he adds. "But the question is, ‘What are we to demonstrate?’"
Sperwer was fitted with GPS for positioning, a Mode C transponder for surveillance on the ground, and an onboard VHF transceiver through which air traffic control can communicate with the UAV operator.
Pignot argues that Sperwer surpasses manned aircraft in terms of see and avoid. "It has a color video camera below the nose with a field of view comparable to that of a human," he says. "In addition, it has its mission cameras–a high-definition black-and-white camera and an infrared camera–with 360-degree fields of view, and these can be used for situational awareness when not doing mission work."
Paris-based SAGEM holds orders for the Sperwer from five European countries: France, Sweden, Denmark, Greece and the Netherlands. It produces two versions of the UAV, having recently introduced the Sperwer-LE (long endurance).