Business & GA, Military, Unmanned

UAVs Entering the NAS

By William Reynish | October 1, 2004
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In retrospect, the agreement reached in 1944, called the Chicago Convention on Civil Aviation, turns out to have been remarkable for its prescience. Among many parts of the Convention still relevant today is Article 8, which states:

No aircraft capable of being flown without a pilot shall be flown without a pilot over the territory of a contracting State without special authorization by that State and in accordance with the terms of such authorization. Each contracting State undertakes to ensure that the flight of such aircraft without a pilot in regions open to civil aircraft shall be controlled as to obviate danger to civil aircraft.

Possibly, delegates were influenced by the then ongoing attacks on London by the German Luftwaffe’s V-1 "flying bomb," a pilotless drone that flew under autopilot control to the approximate target area. With its precalculated fuel load expended, the V-1 would nose over and dive to the ground, exploding on impact. Today’s cruise missiles are, of course, the direct descendants of the World War II V-1s. Nevertheless, the signatories of the Chicago Convention, which led to the establishment of the International Civil Aviation Organization (ICAO), clearly foresaw the potential peaceful uses of unmanned air vehicles (UAVs)–and also the need for them to be positively controlled "in regions open to civil aircraft."

Why Civilian UAVs?

There are several reasons why UAVs have entered civil airspace. These are in addition to the military need for UAVs to fly on reconnaissance missions, over long distances, well beyond their normal restricted areas. Indeed, there are even more civilian imperatives where these aircraft make economic sense. Aerial geophysical surveys, low-level pipeline inspections, disaster monitoring and forest fire mapping overflights are among the many applications in which long or repetitious or hazardous tasks can be performed equally well–and sometimes better–by an unmanned aircraft rather than a manned aircraft.

In Japan, UAVs routinely spray crops. In Arizona, the Immigration and Customs Service, an agency of the U.S. Department of Homeland Security (DHS), now is flying two UAVs–equipped with video, infrared (IR) and other sensors–along that state’s border with Mexico. DHS also is said to be considering the use of small, quiet, long-endurance aircraft, equipped with autotracking low-light level TV, IR and similar covert surveillance systems. They would operate at all altitudes, day or night, as elements in the domestic war on terrorism.

And some UAVs, like NASA’s experimental solar-powered Pathfinder flying wing, could one day cruise effortlessly above 100,000 feet for weeks, and even months, at a time while providing environmental data or serving as a communications repeater station. Looking even further into the future, ex-U.S. Marine Corps pilot Fred Smith, founder and chairman of Federal Express, reportedly is intrigued by the potential of unmanned intercontinental freighters.

Yet those officials in Chicago in 1944 could never have foreseen that the first unpiloted aircraft approved to operate in civil airspace would be turbofan-powered and about the size of a DC-3. Northrop Grumman’s Global Hawk first captured world attention in 2001, when it flew 7,500 nautical miles nonstop from the U.S. West Coast to Australia on a totally computer-controlled, automatic flight. And, unlike less capable UAVs, Global Hawk has no surrogate pilot on the ground to guide it. Its onboard computers, preprogrammed with the mission trajectory and coupled with advanced inertial/GPS navigation units, perform the piloting functions. These include the takeoff, a tight spiral climb to Global Hawk’s 65,000-foot operating altitude, a more than 350-knot cruise segment, and a steep, spiral descent at its destination, followed by a fully automatic landing to a full stop. Remarkable performance, indeed, and well deserving of the UAV industry acronym of HALE, for high altitude, long endurance.

However, even though more than 250 different UAV types are estimated to be operational around the world, the Global Hawk remains not just the first, but the only UAV approved to fly in civil airspace. There are three main reasons for this, all of which are unique to that aircraft:

  • Global Hawk climbs and descends within tightly controlled military airspace and cruises well above civil aircraft altitudes.

  • It is built to comply with full military airworthiness standards.

  • And it is exempt from carrying collision avoidance equipment, since no civil aircraft fly above about 50,000 feet.

No other UAV meets all these criteria and most meet none of them.

Stumbling Blocks

But these criteria also are the stumbling blocks to UAVs’ entry into civil airspace. Very few current models are designed to fly at Global Hawk altitudes, and most of the more advanced types–called MALE, for medium altitude, long endurance–are aimed at flight levels below 40,000 feet and down to 18,000 feet — airspace already heavily populated by manned aircraft.

But in controlled airspace below 40,000 feet, regulatory authorities worldwide are expected to require UAVs to operate identically to manned aircraft. UAVs are to receive no special handling by air traffic controllers, who should not even need to know whether or not an aircraft is manned. Regulators also are expected to mandate that all UAVs flying in civil airspace must have a civil or military certificate of airworthiness, which very few possess today. They also must carry an approved collision avoidance system, which has yet to be defined. And while these requirements are no more onerous than those placed on manned aircraft, they do pose demands that the mainly military-oriented UAV industry has not yet faced.

The most exacting assessment to date of these requirements has been conducted by a combined Joint Aviation Authority/Eurocontrol UAV Task Force over an 18-month period during 2003 and 2004 — and whose final draft report Avionics Magazine has obtained.

The critical yardstick that the task force used in assessing UAV operations was whether they met an equivalent level of safety, compared with conventionally manned aircraft. In discussing airworthiness, therefore, the report stated that a civil certificate of airworthiness (or its military equivalent) would be mandatory to enter civil controlled airspace. UAVs, therefore, would need to be built in certified aircraft manufacturing facilities, using approved aeronautical standards and materials, and subject to all the related aviation inspection processes and procedures, followed by rigorous flight test certification. (This whole process would probably force out most of today’s UAVs, many of which have a distinctly homemade appearance.) And since the UAV’s ground control launch-and-recovery facilities are essential to its operation, these also would have to meet full certification standards. Because of their certification status, these facilities and the air vehicle itself would, like conventional aircraft, be subject to an approved ongoing maintenance program, performed only by appropriately licensed personnel in the various disciplines, e.g., airframe, engine, electronics, etc. A high level of protection for the physical security of all ground-based facilities also would be required.

New and extremely stringent integrity and security standards would need to be developed, too, for the UAV’s flight control data links. The links would have to be highly resistant to jamming or hacker attacks or even "electronic hijacking." Few military UAVs operate beyond VHF/UHF line of sight range of their ground-based operators. They, therefore, are relatively limited in the areas they cover, which in turn, limits their application for tasks in controlled airspace.

But more advanced UAVs, such as the MALE machines, will fly much farther, so ground/UAV flight path control communications will need to be either via a satellite link or by "leapfrogging" across an extended network of ground stations. Such an arrangement will place a high demand on the integrity of the satellite and/or VHF/UHF links–which, from a certificate of airworthiness viewpoint, becomes analogous to a manned aircraft’s control system. Approved communications also place demands on the control handover procedure: both the links and the handover need to demonstrate an extremely low risk of failure. Similar standards would apply to the ground controller’s voice or data communication links with air traffic controllers.

Collision Avoidance

The task force also was concerned about collision avoidance, where today’s human "see and avoid" would be replaced by a UAV’s "sense-and-avoid" technology. Many concepts have been proposed for this task, including tracking UAVs by ground radar or installing small radars or other sensors in the UAVs, which would downlink data to the pilot on the ground. Even chase planes that follow UAVs have been proposed–though this would not, of course, be practical for long-endurance flights or DHS covert surveillance operations.

A transponder certainly will be mandatory for unmanned vehicles in civil airspace. But a fully autonomous, onboard traffic alert collision avoidance system (TCAS) or a conventional system is likely to be the eventual solution for many HALE and MALE missions. Such a system would be able to command the UAV to perform avoidance maneuvers without direction from the ground pilot. A conventional TCAS installation, using VHF/UHF downlink/uplink messages to and from the ground operator, may suffice for more closely controlled operations. Autonomous TCAS, however, would be well beyond the budget of most UAV designs, and even conventional ground-linked TCAS would be a costly option, according to industry observers.

Yet the lack of TCAS raises an unusual safety issue. In a potential collision situation today, involving a TCAS-equipped and a non-TCAS transponder-equipped aircraft, the latter will be unaware of the former and continue on its steady course, while the TCAS-equipped aircraft’s computer will command the pilot to perform an evasive maneuver. However, in an encounter between a manned TCAS aircraft and a UAV, the UAV’s sense-and-avoid system may simply alert its ground-based pilot to the approach of another aircraft. In response, the UAV pilot, unaware of the TCAS aircraft’s intention, could also attempt an avoidance maneuver, possibly in exactly the wrong direction, with potentially disastrous results.

(Avionics Magazine discussed the TCAS issue with several UAV industry personnel and discovered a disturbing lack of awareness of the system. For example, one sensor [for avoidance] proposal claims superior performance in clouds, compared with a human pilot’s eyesight. But this concept is based on the assumption that airline pilots only avoid collisions by continuously peering through their windscreens, and not by using TCAS.)

Collision avoidance is the UAV’s Achilles’ heel, and practical all-weather solutions so far appear to be elusive. Nevertheless, with the large number of aircraft flying today, it becomes a critical safety concern at all altitudes, and particularly around the joint UAV/manned aircraft airports that industry advocates foresee in the future.

Boeing and NASA already have studied mixed traffic operations at such airports. In June, the American Society for Testing and Materials (ASTM) published a broad sense-and-avoid design specification standard. But it did not define the sensor technology to be used, and the standard was based on general aviation integrity criteria. In July, RTCA established Special Committee (SC)-203 to investigate sense-and-avoid technologies, with the aim of developing and recommending appropriate FAA legislation.

Crew Licensing

Similar concerns exist about the qualifications of the ground-based UAV pilots. Some suggest that a private pilot license and an instrument rating would be adequate. But many professional pilots question the level of skill and airmanship such an individual would possess, particularly when operating alongside much faster airline jets in high-density airspace.

Even more startling is the suggestion that, since UAV pilots will operate only a ground-based flight deck, they could simply learn to "fly" and accumulate qualifying license hours on that flight deck alone, without needing to leave the ground in a real airplane. Conversely, at a UAV meeting in Washington, D.C., a U.S. Air Force official stated firmly that only qualified Air Force pilots are allowed to control his service’s unmanned aircraft. RTCA’s SC-203 also is charged with reviewing the issues of ground pilot training and qualifications, and making appropriate recommendations.

Access 5

Civil UAV activities in the United States are spearheaded by Access 5, a government/industry partnership of NASA, Department of Defense (DoD) and FAA, along with UAV builders Boeing, Northrop Grumman, Lockheed Martin, General Atomics, Aerovironment and Aurora Flight Sciences. The Access 5 program (full details at was formally launched early in FY2004 under a $101-million NASA grant. The organization’s name stands for its goal: unrestricted "file and fly" access to civil airspace, with five representing the expected number of years to reach this goal. In other words, UAV access to the National Airspace System (NAS) is to be reached by 2009, a date some feel may be optimistic.

In five years the partnership aims to have approval to operate HALE and MALE UAVs in the NAS and in foreign airspace, with particular emphasis on the region from 40,000 feet down to 18,000 feet. The group’s industry members call themselves UNITE, for UAV National Industry Team.

Access 5 activities are supported by technical assistance from other organizations, the most notable being the Physical Science Laboratory of New Mexico State University (NMSU) at Las Cruces. NMSU scientists have developed a comprehensive UAV concept of operations (CONOPS) for NASA and the Access 5 partners. It can be reviewed at

Another group that is active in the U.S. UAV arena is the Association for Unmanned Vehicle Systems International (AUVSI — Devoted to advancing the development and use of unmanned systems and related technologies, AUVSI is a much broader-based organization than UNITE. Its membership includes government representatives, industry and academics. With more general objectives than Access 5, AUVSI aims to cover "everything below 18,000," according to an industry source. The association organizes an annual technical symposium and trade exhibition.

DoD, of course, is deeply involved in UAV operations and in the development of advanced military systems. Yet in the context of global conflicts, long-range UAVs like the Global Hawk and others often must be deployed to distant theaters through the controlled airspace of other nations. An excellent review of military UAV doctrine and future planning is contained in DoD’s 209-page UAV Roadmap, at

Outside the U.S.

Outside the United States a large number of national UAV associations are affiliated with Paris-based Unmanned Vehicle Systems International (UVSI). The organization’s Web site, at, is extremely informative, containing UAV technical data, photographs and other information. It will include the full text, when released, of the final version of the JAA/Eurocontrol Task Force report referred to above.

UVSI’s objectives are wide-ranging. They include involvement in future European UAV legislation, encouraging cooperation with Access 5 and similar top-level international initiatives, and promoting worldwide development of future systems.

Future UAVs

There now seems little doubt that UAVs will be part of civil aviation’s future infrastructure. How significant a part they will play only time will tell. But the level of activity today, and the predicted levels of activity tomorrow suggest that by the middle of the century UAVs could be common elements in our skies.

Equally, there seems little doubt that avionics systems will play an even more essential role, as these vehicles start to enter civil airspace. It will be new world, with new challenges to overcome. But that already was recognized in Chicago back in 1944, when a group of farsighted individuals mapped the future so accurately.

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