UAVs set to mingle with regular traffic

Aviation International News » August 2004
July 16, 2007, 9:30 AM

The recent commencement of low-altitude Customs and Immigration patrols by unmanned aerial vehicles (UAVs) along the Arizona/Mexico border and the earlier nonstop, totally automated, transpacific and transatlantic flights above FL600 by the USAF’s Global Hawk (AIN, December, page 54) are strong signals that one day the altitude gap between these two will close, and we’ll have unmanned aircraft sharing our airspace. When will that day arrive? One organization, the Access-5 consortium of NASA, DOD, the FAA and the leading UAV builders, aims within five years to have UAVs flying on IFR flight plans between FL180 and FL400.

UAVs are no longer oddities, found only in war zones. It is currently estimated that some 32 countries are developing or manufacturing more than 250 different UAVs, which are operated by 41 nations. And while virtually all of these are military machines, a wide range of commercial applications, from agricultural work to very high-altitude telecommunications repeater stations and environmental monitors– where the vehicles could stay aloft for months–will inevitably emerge. In Japan, UAVs are already routinely spraying crops. One result of this progress is a flurry of activity to ensure that today’s level of aviation safety is not compromised.

In June, a European UAV task force led jointly by the JAA and Eurocontrol published a comprehensive report that assessed the implications for UAV operations of all aspects of current civil aviation legislation. The report must have been sobering reading to the UAV community. While it stated that UAVs could, in principle, fly in civil airspace, the report reviewed the numerous legislative hurdles that UAV developers would first need to overcome.

These started with the philosophy that unless they are built for unique and non-conflicting applications–such as low-altitude scientific flights in totally remote areas–UAVs are unquestionably aircraft requiring a full civil certificate of airworthiness. In turn, this means that they must be built in a certified civil facility using approved manufacturing methods and materials and be subject to all the related inspection processes and procedures, followed by approved flight-test certification programs. This in itself could eliminate many of the odder looking, quasi-homebuilt UAVs that one would prefer not to see off one’s wingtip.

But the certificate of airworthiness would extend beyond the actual air vehicle, since its complete flight deck and its launch and recovery facilities would remain on the ground. So the report states that the same standards would apply equally to those parts as well, but with special emphasis on prompt and correct failure-mode recovery. Similarly, extremely stringent integrity and security standards would apply to the flight control and communications datalinks, to prevent jamming or hacker attacks, or even “electronic hijacking.” Also, since blowing up or commandeering a building is probably easier these days than blowing up or commandeering an airplane, security of all ground-based facilities would be a high priority.

Collision Avoidance Concerns
Having met these requirements, the UAV could get airborne. But once in the air, the report states, it must operate just like any other airplane, following all the rules and performing identically in every way. The report stressed that no special handling to accommodate unusual flight characteristics could be allowed, and the fact that it was unmanned should be completely transparent to air traffic controllers.

This, of course, leads to the issue of collision avoidance, described by some as being the UAV’s Achilles heel. The report notes that much work has been done in developing what the industry calls “sense and avoid” technology. Primarily, this depends on a forward-looking, wide-field-of-view, weather-penetrating (and as yet unspecified) sensor to detect other aircraft that might pose a potential collision threat.
When such an aircraft is detected, the pilot on the ground would perform an avoidance maneuver, while ensuring that it did not bring the UAV into hazardous proximity with other aircraft in the vicinity. In July the American Society for Testing and Materials published a design specification standard for UAV sense and avoid systems, but it did not define the sensor technology to be used.

The JAA/Eurocontrol report expressed concern about collision avoidance in a TCAS environment. Few UAVs can afford to carry TCAS, although they will usually carry transponders, and the issue centers on an encounter between a transponder-equipped UAV and a TCAS-equipped airplane. Normally in such an encounter a transponder-equipped, but non-TCAS, manned airplane would be unaware of the TCAS airplane and would continue on its present flight path, while the pilot of the TCAS aircraft would follow a resolution advisory to avoid it. However, the UAV’s sense and avoid system would alert its ground-based pilot of a potential collision, causing the UAV pilot, too, to attempt an avoidance maneuver, with the risk of disastrous results.

AIN’s discussions with UAV industry officials suggest that the TCAS issue is not well understood. But with the very large numbers of TCAS-equipped aircraft flying today, this appears to be a critical safety concern at all altitudes, both VFR and IFR, and particularly around the joint UAV/conventional airports that industry advocates foresee in the future. Boeing and NASA have already studied mixed traffic handling at such airports.

Yet even in unlimited visibility, human pilots without TCAS protection could experience some close calls. Upon seeing and identifying another aircraft, the report notes, pilots instinctively assess its distance from themselves, based on their familiarity with the broad spectrum of aircraft types and their relative sizes, and take action accordingly. But for the most part, UAVs have totally unfamiliar shapes and sizes, and what might at first appear to be a large UAV at a safe distance could turn out to be a small UAV, dangerously close.

Pilot Qualifications
Qualification of the ground-based pilots was another gray area, with the report suggesting that a private pilot certificate and an instrument rating should be adequate. The report mentions one proposal where, since the UAV pilot will be operating only a ground-based flight deck, it might suffice for him or her to learn to fly and accumulate qualifying license hours in that flight deck alone, without ever needing to leave the ground in a real airplane. (At a recent UAV meeting in Washington, a USAF official stated firmly that only qualified Air Force pilots would be allowed to fly that service’s unmanned aircraft.)

Like it or not, however, UAVs are coming to civil airspace, although in perhaps fewer numbers and under more rigorous regulation than many in the UAV industry might have wished. Nevertheless, like their manned predecessors, UAVs will undoubtedly bring benefits to mankind, many of which are possibly still not envisioned.

And even skeptical pilots will recognize some of the present advantages of UAVs, as described in the 209-page UAV Roadmap, released by the Department of Defense in March last year. Former military pilots–particularly those who have been out of uniform for some years–would find the roadmap, at www.acq. osd. mil/usd/uav_roadmap.pdf, a fascinating review of current military doctrine.

To discount the sometimes perceived dangers of UAV operations, the document cites the following safety benefits, condensed here for brevity:
 • A UAV will never be lost due to pilot vertigo.
 • Crew fatigue at the end of missions can cause accidents; robotic aircraft don’t take chances.
 • No UAV will be lost due to get-home-itis.
 • Mishaps caused by failed life-support systems will not occur.
 • Smoke in the cockpit will not distract pilots or obscure vision.
 • Automated takeoffs and landings will eliminate pattern work, reducing accident exposure.

But the list omitted one other benefit: with a UAV, and contrary to tradition, the pilot will no longer be first to arrive at the scene of an accident.

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