How can the separation of unmanned aircraft be monitored and maintained (among other unmanned aircraft and manned aircraft) in the National Airspace System (NAS)? What considerations need to be made for varying sizes (i.e., Group 1 to 5) and airframes of UAS (e.g., fixed-wing, rotary-wing, and lighter than air)? What technology is currently employed by manned aircraft and is it adaptable for use with unmanned?
An aircraft in flight under VFR conditions fulfills the
separation required from other traffic in reliance on the pilot’s visual
perception. An IFR flight relies on a
number of airborne systems to achieve the separation between traffic. Most of these systems are transponder based,
like the automatic dependence surveillance- broadcast (ADS-B), the secondary
surveillance radar (SSR), and the traffic collision and avoidance (TCAS). In 2012, the FAA published a roadmap for unsegregated
integration of UAS into the national airspace (NAS), the requirement to achieve
a sense and avoid (SSA) capability equivalent or better than manned flights is a
primary requirement to allow such operation.
ATC control relies on SSR broadcast by aircraft transponder
to provide and monitor traffic separation, operating in busy airspace classes
A, B, C, and D requires a transponder as a prerequisite for all participants. UAS are expected to rely on modified variants
of transponder-based systems to achieve the anticipated SAA function.
Transponders are classified as types A, C, or S. The main difference is the capability to
transmit an increased number of flight parameters (Angelov,
2012).
ADS-B represents an improved variant of the transponder
system. However, it can transmit a large
number of parameters, and it can uplink data communication to the
aircraft. The datalink can be ground
based or satellite based. It is
anticipated that future systems will rely on ADS-B technology to downlink UAS
flight parameter and will allow the uplink of executable ATC commands.
UAS will require a collision avoidance function that is
similar to TCAS. When the UAS encounters
a conflicting traffic, it will dully follow the resolutions issued by the
collision avoidance function and this will have priority over any control
command until the conflict situation is resolved (Angelov,
2012).
UAS operations in the NAS will require a variety of
equipment. In general, the larger and
more autonomous vehicles will require more complex sense and avoid equipment. Smaller UAS may utilize cellular
communications as their datalink (Angelov, 2012). Larger UAS will require alternatives that are
more sophisticated. Highly autonomous
UAS need to assure safe operations under all conditions, which requires system redundancies,
and well-established protocols that cover abnormal and failure situations.
References
Angelov, P. (2012). Sense and avoid in UAS. Hoboken,
N.J.: Wiley.
Austin, R. (2010). Unmanned
air vehicles. Chichester, West Sussex, U.K.: Wiley.
SKYbrary. (2016). Automatic
Dependent Surveillance Broadcast. Retrieved 10 October 2016, from http://www.skybrary.aero/index.php/Automatic_Dependent_Surveillance_Broadcast_(ADS-B)
