Detect, Sense and Avoid (Expanded Version)

Highly reliable detect, sense and avoid (DSA) technology as early as 2012 could begin to liberate large unmanned aircraft systems (UAS) from most of today’s restrictions on sharing the U.S. national airspace system (NAS), according to several UAS manufacturers.¹

In presentations to the U.S. National Transportation Safety Board (NTSB) Public Forum on Unmanned Aircraft Systems in April 2008 in Washington, however, they voiced concerns about whether UAS safety policy, airworthiness standards, operating regulations and other prerequisites for this coveted, relatively “unfettered” integration of UAS into the NAS will be ready in this time frame. Airlines, airline pilots and general aviation representatives told the forum that they support this integration so long as safety issues are addressed.

The typical UAS comprises an unmanned aircraft (UA) without a cockpit; a ground control station (GCS) occupied by the pilot(s) and other mission specialists; and command, control and communication equipment and data networks that link the GCS and the aircraft. The DSA avionics envisioned would enable a UAS to respond immediately, autonomously and safely to a collision threat in a manner equivalent to — or possibly better than — pilots of manned aircraft, who can see and avoid other aircraft, visually comply with air traffic control (ATC) vectors/instructions for separation, and respond to a resolution advisory from a traffic alert and collision avoidance system (TCAS II). Efforts also are under way to cross other hurdles, such as the lack of radio frequency spectrum exclusively for UAS command, control and communication, the manufacturers said.

Prompted by the implications of the first two UAS accidents in the NAS to be investigated by the NTSB — one in 2006² (ASW, 12/07, p. 42) and one in 2007,³ the forum contrasted future integration of UAS into the NAS with current U.S. Federal Aviation Administration (FAA) certificate of waiver or authorization (COA) operations and other alternate means of regulatory compliance now available to the UAS industry. The NTSB has issued 22 UAS-related safety recommendations and invited public comment during a period that ended June 30, 2008, on rule making to amend definitions in NTSB Part 830.2 to define an unmanned aircraft accident and related notification requirements for public and civil UAS.⁴ “NTSB does not want to pick up [aircraft] pieces five years from now and say, ‘Why didn’t we think of this?’” NTSB Member Steven Chealander said, referring to the board’s interest in proactive mitigation of UAS risks.

Participants also saw a case study of U.S. National Aeronautics and Space Administration (NASA) missions that helped to save lives and property during wildfires in California and other Western states. Other forum presentations covered the perspectives of other NAS users; UAS equipment design standards, airworthiness and maintenance; and human factors.

NTSB members and staff asked the presenters for clarification on the likely data sources that accident investigators would be able to obtain for a UAS accident in the NAS. None of the large UAS discussed during the forum typically carries a digital flight data recorder, the presenters said. They suggested, however, that possible post-crash data sources might include computer hard drives inside the GCS containing UA telemetry data such as commands and confirmations of command execution, data for GCS system-health parameters, GCS computer fault logs, limited pitch/roll data stored in the autopilot memory and flight computer memory of the UA, and separate data-logger devices.

Wildfires and Pipelines

The NASA wildfire missions and U.S. Department of Energy applications were selected by the NTSB as prominent examples of non-military uses of UAS in the NAS. Historically, scientific projects involving UAS were conducted mostly within restricted areas, said Brent Cobleigh, deputy mission director for exploration, NASA Dryden Flight Research Center. NASA’s uses for the General Atomics Predator B, for example, include surveillance of hurricane formation in the eastern Caribbean, polar ice melt measurement and high-altitude atmospheric research of long duration, he said. Wildfire overflights first were demonstrated in 2006 during two flights by a General Atomics Altair, a variant of its Predator B, including one 16-hour mission under emergency conditions in which five firefighters had been killed.

In a cooperative emergency fire fighting support mission with the U.S. Forest Service and the National Interagency Fire Center, eight Predator B flights were conducted in mid-2007 with durations as long as 20 hours, Cobleigh said. On some, the aircraft loitered about one hour over each of 10 fires at locations in several states. It transmitted burn-area emergency response imagery — detailed, color thermal-infrared pictures for mapping — for use by firefighters within five to 15 minutes. The NASA mission planning involved preselection of more than 280 primary and secondary emergency landing sites based on minimum glide distance from Flight Level (FL) 230 (about 23,000 ft).

The FAA’s operational requirements for these NASA missions were typical for public UAS flights in the NAS, requiring navigation and strobe anti-collision lights; mode C transponder; fully operational redundant flight controls and navigation systems; a chase aircraft with a visual observer below Class A airspace when outside segregated airspace; two-way radio communication with ATC; ATC radar surveillance for collision avoidance above FL 180; climbing to cruise altitude inside a restricted area before exiting into the NAS; flight operations in one of two altitude blocks — 18,000 ft–FL 290 or assigned flight levels above FL 410 — because the UAS was not certified for reduced vertical separation minimum; telephone backup for GCS pilot–ATC communication; immediate notification of ATC following lost link; flight clear of clouds; restriction on operation in greater than light turbulence; pilot/observer qualifications; and mandatory reporting of deviations from these requirements, lost link, incidents/accidents or any occurrence that could increase risk within the NAS.

The many public-sector operators of UAS could help reduce their risks while flying in the NAS by voluntarily adopting airworthiness, flight operations and pilot qualification standards equal to or stricter than the FAA’s requirements for manned commercial aviation, said Randy Stewart, senior aviation policy officer, U.S. Department of Energy. Examples of the department’s civil UAS applications include low-cost pipeline patrol and response to biological or radiological events without concern about pilot exposure.

“We currently have 17 COAs for UAS operations with six aircraft types in 2008–2009,” Stewart said. By tightening standards in recent years, the department experienced — for manned aircraft and UAS combined — a 92 percent reduction in its fatality rate to 0.67 per 100,000 flight hours and a 64 percent reduction in its aircraft accident rate to 2.0 per 100,000 flight hours, he said. The department’s current level of UAS safety reflects a significant change of perspective compared with 1994, when “nobody considered a UAS an aircraft and nobody believed that [FAA] airworthiness standards for aircraft applied to a UAS,” he said.

Officials’ negative attitudes about the value of airworthiness standards for UAS began to shift in 1995, he recalled, after the manufacturer of the Altus UAS found four design flaws and then implemented changes based on a comparison of its design to U.S. Federal Aviation Regulations (FARs) Part 23 requirements. One challenge for large federal departments has been simply identifying/categorizing equipment as aircraft or models.

“I sent out a survey to Department of Energy employees, and one guy wrote back and said, ‘I have a flying robot.’ I asked him to send me a picture. When I saw it, I told him, ‘Yeah, that’s an aircraft.’ … We still have a few UAS of 1.0–2.0 lb [0.5–0.9 kg] that have slipped through the cracks; we are trying to get a hold on those kind of activities.” Without an FAA scheme to categorize UAS, however, the department has issued and revised its own definitions and distinctions in the interest of safety.

“We cannot wait until 2015 or 2025 — we have ongoing operations, and as a department we have to formulate policy that is adequate for the scope of our operations,” Stewart said. “Something needs to be done to keep [UAS integration] on track now because UAS activity is occurring now.”

Scientific researchers in some federal agencies remain unaware that they need to obtain a COA before operating even a small UAS in the NAS, several presenters said. Janet Dobbs, representative of the Interagency Committee for Aviation Policy, told the forum that this problem is being addressed. “We will provide the FAA the inventory of UAS in the federal government, which we have not done in the past, so they can assure they have proper workload planning in the future,” Dobbs said. Fiscal 2009 will be the first year that this committee will report to the Office of Management and Budget about the details of the federal government’s entire UAS fleet, she said.

What They’re Like to Fly

Flying a UA in visual meteorological conditions (VMC) in the NAS was described by some presenters as “learning to fly a camera” and “looking through a soda straw” because sight is the only sense used by UAS pilots. They compared the experience to flying with only one eye that has a 30-degree angle of view.

UAS typically have no provision for the pilot to directly actuate the control surfaces of the aircraft. Instead, the pilot’s commands are carried out by a flight computer/autopilot that actuates the control surfaces. When the UA is not within line-of-sight with the GCS, each command is delayed approximately two seconds by the satellite communication link. UAS pilots generally can comply within seconds with ATC radar vectors during a flight, but, in some cases, the GCS requires modification. For example, before issuing a COA for the multi-state 2007 flights over wildfires by NASA’s Predator B — named Ikhana — the FAA required that the pilots be able to comply with ATC instructions to fly directly to waypoints defined by distance measuring equipment (DME) and a radial of a VHF omnidirectional radio (VOR) station.

“This airplane only had a global positioning system [GPS] receiver and inertial navigation system … so we purchased commercial software to depict routes, VORs [and latitude and longitude of charted waypoints on a separate display],” recalled Col. Mark Pestana, a research pilot and project manager who flies the Predator B at the NASA Dryden Flight Research Center.

Some differences between the current pilot–avionics interface in the GCS compared with a manned aircraft cockpit, Pestana said, could be considered “examples of human factors shortfalls.” For example, when ATC asks a NASA Predator B pilot to “ident” on the transponder, the pilot uses a trackball to move a cursor to one of several display screens, selects a menu, then selects a list of windows and finally clicks on a graphical IDENT button in one of the windows.

Voluntary Safety Reports

A forum presentation by National Air Traffic Controllers Association (NATCA) noted that a few safety-related occurrences involving UAS in the NAS have been reported to NASA’s Aviation Safety Reporting System (ASRS), such as:

• An Embraer ERJ-146 airline crew responded in August 2006 to a TCAS II “climb” resolution advisory because of a 500-ft altitude deviation by the military pilot of a Pioneer UA maneuvering outside a restricted area and 500 ft above the vertical boundary of adjacent Class D airspace.⁵
• A 700-ft altitude deviation in the NAS by the military pilot of a Global Hawk occurred under instrument flight rules (IFR) in February 2007.⁶
• Despite hearing the recorded announcement on an automated weather observing system in March 2007 about an unidentified type of UA and its Cessna 180 chase aircraft operating under VFR near the departure airport, the corporate pilot of a Mitsubishi MU-300 Diamond reported coming “in close proximity” to this eastbound flight of two while climbing about 6 nm (11 km) west of the airport. Neither the UAS pilot nor chase aircraft pilot, also operating under VFR, made any unicom broadcasts of the flight’s position from the airfield, altitude, direction of flight or intentions, the report said.⁷
• The pilot of a Predator operating under IFR in April 2007 and climbing to FL 190 as cleared by a departure controller, subsequently was instructed by an air route traffic control center controller to level off at 17,000 ft, in violation of the COA issued by the FAA for operation of this UAS. The UA pilot continued the climb, and the controller amended the clearance for FL 190 but told the pilot that an ATC instruction had been violated. Subsequent investigation found that the controller was required to comply with provisions of the COA in issuing climb instructions to the UAS.⁸
• In May 2007, an FAA ATC facility information system advised all controllers that two restricted areas were “cold” — inactive — until the following day. The controllers expected to vector civil air traffic through these areas, but had not yet done so when they identified a radar beacon target in one of the restricted areas that matched the flight profile of a UA. The military ATC facility responsible for activity in the restricted areas confirmed that both areas were “hot” — active — from the surface to 13,000 ft for part of that day and that the FAA’s system was wrong.⁹

FAA Flight Restrictions

The current policies and regulations enable two basic categories of UAS operation, said Doug Davis, manager of the 2-year-old FAA Unmanned Aircraft Program Office. One category enables unrestricted flights by military/government UAS operators — which are responsible for their own airworthiness — in airspace that is segregated from NAS users. The other category generally enables, on a case-by-base basis, restricted flights in the NAS if either the military/government operator or the FAA has certified the UAS airworthiness. Operators that primarily use segregated airspace — special use airspace comprising restricted, prohibited and warning areas — include military services and government agencies, collectively called public users.

To enable flights in the NAS by public users, the FAA for 10 years has been granting COAs; 82 COAs were active as of April 2008, said Ardy Williams, air traffic manager–UAS, FAA Air Traffic Organization. Twenty-four COAs were issued in 2004, 54 in 2005, 102 in 2006 and 85 in 2007. About 70 percent are renewals of one or more COAs. Each is basically a waiver of some FARs, with risk mitigation by specifying operating limitations, for periods of three to 12 months. The FAA projects that up to 400 applications for COAs will be received in 2013, depending on regulations in effect then and other factors.

To enable flights in the NAS by a civil user, an entity other than a public user, the FAA can grant either a special airworthiness certificate, typically in the experimental category, or a type certificate. In each case, the FAA itself has certified the airworthiness of the UAS. The FAA issued its first special airworthiness certificate of this kind in 2005 for NASA’s Altair and subsequently issued 26 more special airworthiness certificates in the experimental category.

The normal time required to process each COA is 60 working days. During emergencies, however, some COAs have been processed in minutes to hours, Williams said. A secure Web site used to process COA applications also contains the March 2008 version of FAA’s interim guidance for public users and civil users of UAS to study.¹⁰ One special COA template is used for rapid natural disaster relief and another special COA template is used for immediate military/government use of Predator-class UAS during an emergency situation.

Around mid-2008, the FAA expects to complete a revision of its strategic road map for regulation of UAS with improved definition of work assignments, Davis said. Related activities include a focus on guidance for issuing special airworthiness certificates in the restricted category; review of applicability of FARs Part 23 airworthiness regulations to UAS; review of applicability of FARs Part 27 rotorcraft regulations to UAS; review of GCS technology; and review of automatic takeoff and landing technology.

The UAS community has the perception that near-term avionics solutions for command and control and DSA functions alone would enable UAS operations in the NAS to become much more similar to those of manned aircraft, Davis said. “The reality is we have got a lot of work to do in developing the airworthiness standards and the certification standards for how UAS are going to integrate … developing pilot qualifications and training materials for our safety inspectors out in the field and our aircraft certification engineers … [and adding UAS pilot/observer] medical standards.”

Although a 2007 DOD road map anticipated such a UAS capability to “file and fly” in the NAS by 2012, Davis said, “Detect, sense and avoid technology will not be ready by then. The biggest obstacle is the amount of work that needs to get done [by the FAA].”

He noted that with FAA oversight and involvement of the U.S. Department of Defense (DOD), RTCA Special Committee 203 (SC-203) since 2004 has pursued consensus civilian standards for DSA functions and command-and-control functions for UAS among other tasks.¹¹ “Somewhere in the realm of 2020–2025, we will see a fully certificated avionics suite that will meet the full FAA requirement for civil UAS applications,” Davis said.

The FAA Unmanned Aircraft Program Office and Air Traffic Organization are developing several initiatives to study the effects of the growth of UAS operations on air traffic control and to provide standardized training on UAS to all air traffic controllers. “We routinely restrict the simultaneous or concurrent operation of unmanned aircraft with civil manned operations [in airport traffic patterns], particularly at civil use airports [and civil-military joint-use airports] that allow for those types of operations,” added Bruce Tarbert, NAS Integration Team lead in this office. “We develop [airport] procedures on a case-by-case basis [and] ensure that a notice to airmen is issued. … If airfields are uncontrolled, we require UAS pilots to monitor the common traffic advisory frequency or unicom frequency … as a [risk] mitigation requirement.”

Davis said that the FAA has prioritized these UAS activities based on industry economic projections. “We found several market surveys that indicated that over the next seven to eight years, the preponderance of unmanned aircraft are going to be under 20 lb [9 kg], so clearly we have a market need that is driving the direction that we are taking,” he said.

Among other primary FAA activities to develop new policy, regulations and/or regulatory amendments and guidance for civil commercial UAS is a new aviation rulemaking committee that began meeting in May 2008. This committee will draft a regulation for the line-of-sight commercial use of UAS during daylight hours under visual flight rules [VFR] with limitations on maximum weight, airspeed and altitude, Davis said. “Hopefully, if everything goes well, we will see a final rule in the 2010 to 2011 time period,” he said. “It is a very conservative approach to begin with because we need to minimize the risk while enabling an economic opportunity to take place.”

Military Priority

U.S. military services have developed UAS risk-analysis processes and safety mitigation methods that are instructive for operating civil UAS in the NAS, said Lt. Col. Charles Kowitz, chief of unmanned aircraft systems safety, U.S. Air Force Safety Center, citing examples from a safety assessment report requested by the FAA for the Northrop Grumman RQ-4 Global Hawk.

Assessment of 20 hazards affecting Global Hawk operations showed that risks of operating a UAS in the NAS can be more extensive and subtle than the risk of midair collisions. “If an unmanned aircraft creates deviations of altitude that unnecessarily preoccupy the attention of an air traffic controller, [that] essentially decreases the safety factor afforded to all the other participants in the NAS at the time,” he said.

The main advantage of keeping a military UA inside special use airspace is the pilot’s ability to fly “unfettered” compared with the constraints in the NAS, noted Lt. Col. Dallas Brooks, chief, unmanned systems integration policy, DOD Policy Board on Federal Aviation. “We have done a lot in the past to keep our major UAS operations away from heavily populated traffic areas,” Brooks told the forum. “As mission needs increase, however, the pressure is on for more UAS operations and training, and it gets harder to do that. … As a last resort when we cannot use a COA … we consider, with great reluctance, a temporary flight restriction that essentially sterilizes airspace for our use.”

A 2007 DOD–FAA memorandum of agreement created the opportunity to operate small military UAS in Class D airspace at about 100 DOD-controlled, non-joint-use airfields. “For small UAS — 20 lb [9 kg] or less — operations also can be conducted in Class G airspace, in most cases from the surface to 1,200 ft above ground level [AGL] as long as we are over DOD-controlled lands, meaning bases and ranges,” Brooks said. “This gave us access to quite a bit of airspace — 31,336 sq mi [81,160 sq km].”

Welcome to the NAS

Mont Smith, director of safety, Air Transport Association of America (ATA), told the forum, “This is a time in the history of airlines when finding methods to support the integration of UAS in the NAS — without causing delays, capacity reduction or placing current NAS users at increased risk — is of utmost importance to us.” Nevertheless, ATA member airlines also have concerns — such as the risks of operating a 4.0-lb (1.8-kg) aircraft, for example, at or below 400 ft AGL in Class B or Class C airspace — because of potential proximity to an airliner that has experienced a failed engine at low altitude or is maneuvering during a required navigation performance (RNP) area navigation (RNAV) approach.

The greatest risk posed by a UAS to an airliner would be “an unguided, dark UA” that is flying through occupied/congested airspace of the NAS without replying to transponder interrogations of its position and altitude, he said. The ATA recommended that all UAS approved to operate in or near high-density traffic areas should have:

• GCS controls and displays with the “look and feel” of manned aircraft;
• Assessment of all human factors affecting the “synthetic cockpit”;
• Full-motion flight simulator training for pilots of future “ultra-large payload” UAS; and,
• Synthetic vision/virtual reality display systems in the GCS that engage the attention of UAS pilots and help them maintain tactical situational awareness.

Airline Pilot and Controller Input

In May 2007, the Air Line Pilots Association, International (ALPA) adopted a policy of continued participation in FAA-industry efforts to safely integrate UAS into the NAS, said Ellis Chernoff, an airline captain and representative of the ALPA National Airspace Modernization Team.

“The end game is to have fully normalized, seamless UAS operations in the NAS,” Chernoff said. “Airline pilots should not even notice that there are unmanned aircraft up there. … ATC rules must be the same regardless of the aircraft type.”

Yet ALPA continues to draw industry attention to several issues:

• Standard operating procedures for in-flight emergencies vary among UAS types and operators, making it difficult for other NAS users to anticipate UA flight paths;
• Nonstandard pilot–ATC communications, such as telephone, should be acceptable only for UAS operating under a COA or special airworthiness certificate, and signal latency issues must be addressed for safety; and,
• In addition to collision risk, a UA that deviates from its assigned flight path or taxi instructions, causes an airport shutdown for an emergency landing, or strays into the approach paths of an airport could require pilots of manned aircraft to conduct a costly go-around with some increased risk involved.

All controllers need adequate UAS-related training, said Darren Gaines, air safety investigator and chairman of the NATCA Air Safety Investigations Committee. “Controllers know that UAs come in a wide variety of shapes, sizes, costs, performance dynamics, speed, climb rate, maneuverability and turning radius — but these are all things that are new to us, and we have to have a handle on them when more UAs start mixing it up with … conventional aircraft traffic,” Gaines said. “We are starving for information. We are unfamiliar with UAS operators’ contingency plans and emergency requirements. We don’t know [whether manned aircraft] pilots are familiar with the performance characteristics of UAs.”

NATCA’s concerns include problematic assumptions about pilots’ capability for visual contact; uncertainties about wake turbulence and cloud clearance; nonstandard communication methods; and incorrect use of ATC flight-following services.

“So much of what we do in ATC is visual when aircraft operate in Class B and Class C airspace or when operating visually,” Gaines said. “The see-and-be-seen requirement seems to be deficient — the UAS pilots are not able to visually acquire aircraft in the vicinity, but a lot of the time, to maximize capacity, we expect [pilots] to visually acquire and follow another aircraft to a runway or to an airport, and to maintain that aircraft in sight.”

Two examples of unexpected behavior by UAS pilots and their chase aircraft pilots during flights in the NAS were cited, although the errors were not unique to UAS pilots. During several flights at one location, UAS pilots requested flight-following service from ATC while operating under VFR but after hearing the controller respond with the phrase, “radar contact,” they went off the ATC frequency for the duration of the flight, leaving controllers unable to provide traffic advisories and other safety information, Gaines said.

A formation flight of two aircraft normally is handled as one aircraft by ATC. “A chase aircraft is supposed to be in formation with the UA, at the same altitude within 1.0 nm [1.9 km],” Gaines said. “[In one case,] when controllers exchanged traffic information about the UA with aircraft in the area, the other pilots reported that the chase aircraft was more than a mile away and not at the same altitude.”

UAS Manufacturer Insights

Pilot-UA interfaces have been a strong focus of attention by manufacturers, said Thomas Bachman, director, One System Common Systems Integration Team, AAI Corp. His company, for example, is working with the U.S. Army Aviation Engineering Directorate on common GCS designs for multiple types of military UAS based on a North Atlantic Treaty Organization standard for a more common architecture than used in the past, he said.

“GCSs were stove-piped — designed for a very specific UAS, built uniquely for the U.S. Department of Defense and taken into the field very quickly,” Bachman said. “They were not really designed using established aircraft certification standards. Over the last four to five years, this has changed dramatically [toward designing] GCSs to the same standards as manned aircraft.”

The UAS industry is seeking incremental access to the NAS over time, he said. But this will require near-term federal government funding to develop DSA; allocation of airspace other than military test ranges and NASA restricted areas as safe test areas for UAS; high priority to certification of data links and spectrum allocation for UAS; completion of civil safety requirements and airworthiness certification standards; and a process for certifying subcomponents of UAS instead of complete systems only.

Trends in military UAS that also should influence civilian UAS applications include common control systems with UA-specific software modules, applying human factors knowledge from manned aircraft but recognizing different needs of unmanned aircraft, and methods of preflight planning using digital terrain maps to ensure line-of-sight data link and minimum terrain clearance at all times.

A UAS manufacturer can ensure that unmanned aircraft are developed and tested with the same overarching safety policies applied to manned aircraft, said James Martin, program manager, A160 Hummingbird Program, Boeing Integrated Defense Systems. Most Boeing types have been developed as public use aircraft, so internal manufacturing processes have had to match what different government customers specified, Martin said. As full integration of UAS into the NAS becomes feasible, however, there will have to be top-level policy that ensures consistent standards for airworthiness of all civil platforms, he said.

Frank Grimsley, director of engineering, 303rd Aerospace System Wing, Wright Patterson Air Force Base, said that the U.S. Air Force routinely and simultaneously operates both its manned military aircraft and its largest UAs in the same airspace and from the same airfields, and has gained experience operating in civil airspace worldwide.

The Predator series and Global Hawk have been granted restricted Air Force airworthiness certification for operation in the NAS because they currently do not meet all airworthiness criteria — such as bird strike tolerance and fuel system redundancy — required by the joint military standards for manned aircraft, Grimsley said.

Sam Richardson, liaison to the FAA for experimental aircraft airworthiness certification and logistics program manager for the Sky Warrior/Extended Range Multi-purpose Program at General Atomics Aeronautical Systems — which manufactures the Predator UAS series — said that all variants of Predators combined had logged more than 450,000 hours by April 2008 and fly about 17,000 hours per month. Three of the company’s UAS — Altair, Sky Warrior and Predator B — have military airworthiness certification by the DOD and FAA special airworthiness certification for restricted operation in the NAS, Richardson said. In April 2008, the Predator B also received FAA airworthiness certification under the agency’s interim national policy.¹² “These aircraft are instrument flight rules [IFR]–capable and are currently flying IFR missions … over five continents, five oceans and many seas,” Richardson said. “They are interspersed with manned aircraft coming in and out of international airports. The DOD’s [UAS road map] — projecting file-and-fly capability by 2012 — is something that we really need to try to achieve rather than a 20- to 25-year process.”

Among factors favorable to Predator B integration into the NAS are triple-redundant flight control computers, triple-redundant avionics, dual-redundant flight control surfaces, dual alternators, dual systems for automatic takeoff and landing and a deicing system, he said.

The Global Hawk also provides an example of technologies relevant to UAS integration into the NAS, said Alfredo Ramirez, chief architect, High Altitude Long Endurance Systems Enterprise, Northrop Grumman Integrated Systems.

Capabilities favorable to its integration into the NAS include redundant data links; programmed primary flight plan routes, contingency routes and lost communication routes; diversion airfields and ditch points; avionics power backup; pilot authority to override the programmed mission plan; requirement for pilots to confirm every command before transmission; redundant pilot-ATC voice relay links through the aircraft; synchronized dual flight computers to control flight, autonomously manage system functions and monitor performance of the other computer; and autonomous reporting of subsystem malfunctions.

Air Force researchers and Northrop Grumman were working as of April 2008 on flight tests of DSA systems. “Detect, sense and avoid research is well under way,” he said. “The surrogate UAS — a Calspan Flight Research Group Learjet outfitted with electro-optical radar-ranging, TCAS inputs and ADS-B inputs — fuses all of this data to provide a resolution to the flight computer, so that [the autopilot] takes autonomous action, which is immediate. It is not inconceivable for this technology to be ready for use in a UAS in a matter of a couple of years. In five years, we could already be getting technical data to demonstrate its robustness.”

Notes

1. For purposes of approving UAS operations in the NAS, FAA guidance “applies only to those UAS operations affecting areas of the NAS other than active restricted, prohibited or warning areas,” the FAA said. NTSB forum presenters used the term NAS in this context.
2. Regarding the April 25, 2006, crash of a Predator B UAS operated by U.S. Customs and Border Protection near Nogales, Arizona, the NTSB said that it “found that several factors related to pilot training and proficiency in dealing with emergency situations contributed to the accident” and identified other safety issues involving UAS equipment design and maintenance, operational contingency plans, safety risk management for UAS operation in the NAS and air traffic management of UAS.
3. NTSB’s accident report on the Aug. 24, 2007, crash of a Raytheon Cobra, a small UAS, at a private airport in Whetstone, Arizona, said that the probable cause was a “student pilot’s failure to follow proper procedures, specifically not verifying that the mode switch [of the manual pilot console] was in the automatic position before changing the pilot [data-link] address, which resulted in loss of aircraft control.” The console was being used to control two Cobra UAs at the time of the accident.
4. NTSB. Notice of Proposed Rulemaking. Federal Register Volume 72 (March 31, 2008) p. 16826. Amendment of NTSB Part 830, Notification and Reporting of Aircraft Accidents or Incidents and Overdue Aircraft, and Preservation of Aircraft Wreckage, Mail, Cargo, and Records.
5. NASA ASRS report no. 707636.
6. NASA ASRS report no. 727848.
7. NASA ASRS report no. 732137.
8. NASA ASRS report no. 734867.
9. NASA ASRS report no. 737060.
10. FAA Order 8130.34. “Airworthiness Certification of Unmanned Aircraft Systems.” March 27, 2008. This national policy established procedures for issuing special airworthiness certificates in the experimental category to operate UAS for research and development, market survey or crew training.
11. RTCA SC-203, established in October 2004, has published one of four planned products: Guidance Material and Considerations for Unmanned Aircraft Systems, issued in June 2006. Dates for issuing Minimum Aviation System Performance Standards (MASPS) for Unmanned Aircraft Systems; MASPS for Command, Control and Communication Systems for Unmanned Aircraft Systems; and MASPS for Detect, Sense and Avoid Systems for Unmanned Aircraft Systems were yet to be determined as of June 2008.
12. FAA. “Unmanned Aircraft Systems Operations in the U.S. National Airspace System.” Interim Operational Approval Guidance 08–01. March 13, 2008. This document explains requirements and restrictions affecting UAS operations implemented by written agreement between the FAA and the UAS operator.

Further Reading From FSF Publications

FSF Editorial Staff. “See What’s Sharing Your Airspace.” Flight Safety Digest Volume 24 (May 2005).