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primary restriction to normal operations of UA. The intent of “see and avoid” is for pilots to use their
sensors (eyes) and other tools to find and maintain situational awareness of other traffic and to yield the
right-of- way, in accordance with the rules, when there is a traffic conflict. Since the purpose of this
regulation is to avoid mid-air collisions, this should be the focus of technological efforts to address the
issue as it relates to UA rather than trying to mimic and/or duplicate human vision. In June 2003,
USAF’s Air Combat Command (ACC) sponsored a joint working group to establish and quantify a S&A
system capability for submission to the FAA; their White Paper, See and Avoid Requirement for
Remotely Operated Aircraft, was released in June 2004.
Relying simply on human vision results in mid-airs accounting for an average of 0.8 percent of all
mishaps and 2.4 percent of all aviation fatalities incurred annually (based on the 3-year average from
1998 to 2000).4 Meaningful S&A performance must alert the UA operator to local air traffic at ranges
sufficient for reaction time and avoidance actions by safe margins. Furthermore, UA operations BLOS
may require an automated S&A system due to potential communications latencies or failures.
The FAA does not provide a quantitative definition of S&A, largely due to the number of combinations of
pilot vision, collision vectors, sky background, and aircraft paint schemes involved in seeing oncoming
traffic. Having a sufficient field of regard (FOR) for a UA S&A system, however, is fundamental to
meeting the goal of assured air traffic separation. The FAA does provide a cockpit field of regard
recommendation in its Advisory Circular 25.773-1, but the purpose of AC 25.773-1 does not specifically
mention S&A.
Although an elusive issue, one fact is apparent. The challenge with the S&A issue is based on a
capability constraint, not a regulatory one. Given the discussions in this and other analyses, a possible
definition for S&A systems emerges: S&A is the onboard, self-contained ability to
􀂾 Detect traffic that may be a conflict
􀂾 Evaluate flight paths
􀂾 Determine traffic right-of-way
􀂾 Maneuver well clear according to the rules in Part 91.113, or
3 NOTE: UA operators may, or may not, be "rated pilots." For this Airspace Integration Plan, "operator" is the
generic term to describe the individual with the appropriate training and Service certification for the type of UA
being operated, and as such, is responsible for the air vehicle's operations and safety.
4 National Transportation Safety Board aviation statistics.
UAS ROADMAP 2005
APPENDIX F – AIRSPACE
Page F-8
􀂾 Maneuver as required in accordance with Part 91.111.
The key to providing the "equivalent level of safety" required by FAA Order 7610.4K, Special Military
Operations for Remotely Operated Aircraft, is the provision of some comparable means of S&A to that
provided by pilots onboard manned aircraft. The purpose of S&A is to avoid mid air collisions, and this
should be the focus of technological efforts to address S&A (rather than trying to mechanize human
vision).
From a technical perspective, the S&A capability can be divided into the detection of oncoming traffic
and the execution of a maneuver to avoid a midair. The detection aspect can be further subdivided into
passive or active techniques applicable in cooperative or non-cooperative traffic environments.
The active cooperative scenario involves an interrogator monitoring a sector ahead of the UA to detect
oncoming traffic by interrogating the transponder on the other aircraft. Its advantages are that it provides
both range and bearing to the traffic and can function in both visual and instrument meteorological
conditions (VMC and IMC). Its disadvantages are its relative cost. Current systems available in this
category include the various Traffic-alert and Collision Avoidance Systems (TCAS).
The active non-cooperative scenario relies on a radar- or laser-like sensor scanning a sector ahead of the
UA to detect all traffic, whether transponder-equipped or not. The returned signal provides range,
bearing, and closure rate, allowing prioritization of oncoming traffic for avoidance, in either VMC or
IMC. Its potential drawbacks are its relative cost, the bandwidth requirement to route its imagery (for
non-autonomous systems), and its weight. An example of an active, non-cooperative system that is
currently available is a combined microwave radar and infrared sensor originally developed to enable
helicopters avoid power lines.
The passive cooperative scenario, like the active cooperative one, relies on everyone having a
　
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