The integration of UAS into the NAS is a
challenging process. It is complicated by the fact that UASs simply don’t have
pilots in the cockpit and the same type of manned aircraft equipment like
transponders, traffic collision avoidance system (TCAS), etc, aren’t installed
in the aircraft itself, nor is that information displayed in ground control
stations (GCS) to provide at least some type of traffic awareness. In addition,
the varying groups of UASs that extend from micro vehicles up to large aircraft
and different classes of automation, makes it difficult to apply “a one
solution fits all” approach. UASs have the added benefit of electro-optical and
infrared sensors which could help in maintaining separation from other traffic;
however, more acceptable levels of safety will be needed. More sensors that can
automatically respond or alert the remote pilot in the GCS has been one answer.
The process of UAS separation will depend on a number of factors. Most notably,
those encompass aircraft and GCS equipment, and the type of flight rule is
being used to fly in the NAS.
Currently, on-board pilots, Air traffic
Controllers (ATC) and Air Route Traffic Control Centers (ARTCC) form the
backbone for separation services. ATC/ARTCC’s use radar and satellite based services
to monitor and maintain traffic separation, while on-board pilots use good old
fashion human eyesight. The type of flight rule used, and sometimes the
airspace being operated in, defines the level of responsibility for all of
these parties.
In visual flight rules (VFR) the pilot is
responsible for detecting and avoiding other aircraft traffic. As the name
implies, a pilot can see outside the aircraft and they are primarily
responsible for motioning and maintaining separation at all classes except in class
A where IFR is required (FAA, 2008). In class B and C airspaces, ATC will take
responsbiltiy for separation services regardless of which flight rule is used
(FAA, 2008). In every other case, ATC can provide flight following, workload
permitting, to assist VFR traffic with separation from other VFR traffic but
the pilot is still primarily responisble (FAA, 2008). Class G, E and D
airspaces are; therefore, the most vulnerable when it comes to UAS integration
because the pilot, not ATC, is resposnible (FAA, 2008).
In Instrument flight rules (IFR),
controllers assumes separation duties because these rules imply that the pilot
cannot see outside the aircraft. This area is less vulnerable than VFR as
procedures define terminal and en-route flight paths. However, issues still
exist with safely integrating UAS. ARTCC workload deals heavily with re-routing
and route convergence in the en-route environment due to issues such as:
weather, traffic congestion, and other factors (FAA, 2008 & FAA, 2015). The
dynamic and unpredictable nature of these areas demand attention with respect
to UAS integration. In the terminal environment, ATC workload involves
monitoring procedural departure and approach activity for separation (FAA,
2008). It also entails approving user requested changes to flight plans,
cancelling IFR for VFR, providing radar approach guidance for landing, issuing
directions to amend standard procedures, and etc (FAA, 2008 & FAA, 2015).
In either case, standard procedures are filed and ATC expects pilots to follow
them with zero deviations (FAA, 2012). Traffic sequencing is the biggest issue
here in maintaining separation that should be a focus for autonomous UAS, as
semi and remotely piloted can be adjusted quickly by pilot inputs.
To fulfil the task of monitoring air
traffic and assist in maintaining separation with flight rules and procedures,
ATC/ARTCCs use primary (radar returns) and secondary surveillance radar
(transponders) and it is referred to as positive control (FAA, 2016 & FAA,
2008). Next-Gen efforts are ushering in automated dependent
surveillance-broadcast (ADS-B) as the method to replace both of these systems
(FAA, 2016). The latter moves traffic monitoring to a satellite and datalink
(if user has ADS-B In and is in a certain range) based approach (FAA, 2016). In
addition, ATC carries out broadcasts through the Traffic Information Service –
Broadcast for uncooperative traffic (radar detected, non-ADS-B equipped
aircraft until full integration is completed) and re-broadcasts through ADS-R
for traffic transmitting on the Universal Access Transceiver frequency (FAA,
2016).
For UAS, the easiest answer is make ATC
controllers responsible for traffic separation while operating under VFR, in
addition to IFR, by using primary and secondary radar, and ADB-S later on down
the road. However, this increases ATC workload substantially and doesn’t
necessarily solve the problem for the see and avoid requirement in VFR
operations (Fern, Kenny, Shively, & Johnson, 2012). For UAS groups 1 and 2,
current sizes of transponders are too big and radar may not be able to see UASs
that operate at low altitudes. Thus, internal radar and transponders, or
smaller ADS-B out/in components, are needed to interface with the autopilot
system for autonomous avoidance of other group 1 and 2 UASs. Due to the small
nature of these UAS types and lack of exhaust plumes, it can be hard to detect
them visually through electro-optical or infrared sensors. For UAS groups 3-5,
a combination of any and all these types of sensors should be used. It is
highly recommend that combinations are used as sensor fusion provides a level
of redundancy and accuracy of information.
Levels of delegation offers a different
approach, because it depends on the level of sophistication of the UAS’s sense
and avoidance systems. This allows the proper risks to be managed at the right
level and defines the responsibility between the controller and the UAS pilot.
These levels of delegation are defined as: limited (ATC identifies and issues
direction, pilot performs), extended (ATC identifies and pilot decides and
performs a maneuver) and full (UAS pilot does all three) (Fern, 2012).This
technique could allow UAS integration to happen now for aircraft like the MQ-9,
which possess an electro-optical/infrared sensor to detect air traffic if given
a bearing and range. In addition, it has the required transponder which allows
ATC to obtain altitude, airspeed and heading information necessary for limited
delegation operations. With a sensor and a transponder, the MQ-9 could perform
limited and extended delegated separation. This would be no different than any
other UAS in group 3 to 5 that has the same capabilities. Full delegation is
the biggest issue because it requires the UAS to perform sensing in a timely
fashion. Traditional rotating sensors have soda straw like views (30 degrees to
be exact) and situational awareness is lost as soon as that view is no longer
present, thus a continuous sight picture is not the same as a human on-board
the aircraft would have (equates to 120 degrees or more). Full delegation will
require a combination of sensors dedicated to detecting, sensing, and avoiding
other aircraft.
References
References
FAA. (2008). Pilots Handbook of Aeronautical
Knowledge. FAA.gov. Retrieved from
http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/
FAA. (2012). Instrument Flying Handbook. FAA.gov.
Retrieved from http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-15B.pdf
FAA. (2015). Instrument Procedures Handbook. FAA.gov.
Retrieved from http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/instrument_procedures_handbook/
FAA. (2016). Equip ADS-B: Ins and Outs. FAA.gov.
Retrieved from http://www.faa.gov/nextgen/equipadsb/ins_and_outs/
Fern, L. (2012). UAS Integration into the NAS:
Unmanned Aircraft Systems (UAS) Delegation of Separation. Proceedings of the 2012 Human Factors and Ergonomics Society Meeting. Retrieved
from http://human-factors.arc.nasa.gov/publications/UASIntegrationInto TheNASDelegation.pdf
Fern, L., Kenny, C.A., Shively, R.J., Johnson, W. (2012).
UAS Integration into the NAS: An Examination of Baseline Compliance in the Current
Airspace System. Proceedings of the 2012
Human Factors and Ergonomics Society Meeting. Retrieved from http://human-factors.arc.nasa.gov/publications/UASIntegrationIntoTheNAS.pdf
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