UAS
Integration into the National Airspace System
Shawn
M. Wyne
ASCI
638 – Human Factors in Unmanned Systems
Embry-Riddle Aeronautical
University
The challenges of
managing and coordinating large metal machines moving through air at high
speeds have always been daunting. In the beginning, pilots simply used their
eyesight to avoid hitting other objects and each other. Over time, technology
like radar and airborne radios allowed a measure of direct coordination between
aircraft. In spite of these changes, mid-air collisions between aircraft
continued through the 1950’s and 60’s (Kochenderfer, Holland, and
Crysanthacopoulos, 2012). New technology was required to overcome the obstacles
of increasing air traffic. The Federal Aviation Administration (FAA) enacted stricter
rules and procedures, but this did not solve the problem alone. The
introduction of the Traffic Alert and Collision Avoidance System (TCAS) helped,
and TCAS II equipment became mandatory in the United States in 1990 (Rosenkrans,
2014). This improvement in technology substantially increased flight safety,
just as new technologies did 60 years ago. However, just as it happened before,
the new technology is reaching its limit of usefulness (Wyne, 2015). Continued
increase in air traffic, and in particular the introduction of unmanned
aircraft systems (UAS) into the same airspace, requires another leap in
technological capability. The National Airspace System (NAS) requires an
upgrade of systems and procedures to not only improve safety, but increase
efficiency and maximize use of resources.
The process in which the
FAA is pushing this change is with the implementation of the Next Generation
Air Transportation System (NextGen). The goals of implementing NextGen cover
several areas. The first, as an extension of current systems, is to improve
collision avoidance. A new technology that is helping push NextGen and the
inclusion of unmanned systems is the introduction of Automatic Dependent
Surveillance-Broadcast (ADS-B) equipment. The ADS-B is a replacement system for
transponders currently in use for traffic control (FAA ADS-B, 2015). A
significant problem with current TCAS, radar, and transponders is their lack of
precise information. Radar gives position, but requires a Mode C transponder to
return altitude data. Ground radars typically interrogate every 12 seconds, and
only request altitude data every other interrogation (Richards, O’Brian, and
Miller, 2010). So an average aircraft location is only updated five times per
minute, and altitude only two or three times per minute. The new system of
ADS-B utilizes a completely new approach. It uses Global Positioning Satellites
(GPS) signals to generate a precise location of itself in three dimensions.
Then, it broadcasts detailed position data to other users (Richards, et. al.,
2010). Because it does not rely on a rotating radar dish, it can send
information more frequently, and always include all the data it has. Improved
data quality and rate of data updates will be crucial for collision avoidance
among heterogeneous airborne systems in increasingly crowded airspace. ADS-B
concepts, and the GPS technology behind it, is not particularly recent.
However, it is yet to be fully implemented as a tool. The FAA now requires
ADS-B compliant equipment for all airspace that currently requires Mode C
transponders by 2020 (Babbitt, 2010). As the supporting systems and airborne
equipment are fully developed and implemented, they will provide the structure
to improve automated collision avoidance systems (Wyne, 2015). This is also a
significant addition to UAS operation under potential lost-link behavior. While
still updating position to controllers, and maybe more importantly to other
aircraft, there will remain a system for other aircraft to avoid a UAS not
under positive control.
Another important goal of
NextGen is increasing the overall efficiency of air traffic, especially in the
departure and terminal approach areas of airports. The significant increase in
overall air traffic is overloading the usefulness of the current arrival and
departure procedures. Current flight paths in terminal areas are published,
fixed routes. Since wake turbulence spacing cannot be decreased, there exists a
maximum throughput of aircraft along a single route. NextGen is implementing
satellite-based arrival and departure procedures, which instead of being
singular, can be unique for different aircraft (Carey, 2015). This means more
traffic through a smaller space, since it adds more lateral separation from
following aircraft. This also means more aircraft taking off from a single runway,
a potential increase of 8-12 departures every hour (FAA NextGen Experience,
2015). This cuts down taxi and holding time for aircraft on the ground, which
saves time and fuel. The monetary savings are also significant. US
Transportation Secretary Anthony Foxx stated the savings already realized under
the limited rollout of new procedures is over $2 billion, and expected to
surpass $130 billion over the next 15 years if the system is fully implemented
(Carey 2015). Unique arrival and departure procedures also provide a tool to keep
UAS especially separated from manned traffic, negating some sense-and-avoid
limitations.
Another goal of the
NextGen system is to increase efficiency in the enroute portions of flight (FAA
NextGen Experience, 2015). Similar to arrival and departures, enroute flight
paths also follow published paths, similar to roads on the ground. This is
convenient for controllers because with the current limited position data,
aircraft also have an expected location that can be inferred. The improved
position information allows controllers to send aircraft on more direct paths
to their destination. The improved courses are a major part of the time and
fuel savings air traffic can realize. As a secondary effect, the increased fuel
savings from better routing means a corresponding decrease in emissions. With
about 85000 daily flights within the NAS, this is no small reduction (FAA
NextGen Experience, 2015).
There are other, more
technical pieces to the NextGen system improvements, such as replacing analog
voice systems, improving data dissemination among ground based controllers, and
better integrating weather data into controller decisions (FAA NextGen
Experience, 2015). All these are the backbone pieces to implement the front
side, which is better flight coordination and planning. The ability to control
aircraft to a much more detailed level, send unique and specific flight plan
changes, and keep data consistent among many users will bring significant
improvements to the NAS. Importantly, it provides a level of control needed to
integrate UAS into already congested airspace.
Babbitt, J. (2010, May 28).
ADS-B Out Performance Requirements to Support Air Traffic Control Service;
Final Rule. Department of Transportation Federal Aviation Administration.
Retrieved from: http://www.gpo.gov/fdsys/pkg/FR-2010-05-28/pdf/2010-12645.pdf
Carey, B. (2015, November
2). US Transportation, Industry Officials Upbeat on NextGen. Retrieved from http://www.ainonline.com/aviation-news/air-transport/2015-11-02/us-transportation-industry-officials-upbeat-nextgen
Federal Aviation
Administration (2015). Automatic Dependent Surveillance-Broadcast. Retrieved November
8, 2015 from: https://www.faa.gov/nextgen/programs/adsb/
Federal Aviation
Administration (2015). NextGen Experience. Retrieved November 7, 2015 from https://www.faa.gov/nextgen/experience/?episode=2
Kochenderfer, M.,
Holland, J., and Cryssanthapolous, J. (2012). Next Generation Airborne
Collision Avoidance System. Lincoln Laboratory Journal. Retrieved from: https://www.ll.mit.edu/publications/journal/pdf/vol19_no1/19_1_1_Kochenderfer.pdf
Richards, W., O’Brian,
K., and Miller, D. (2010). New Airborne Surveillance Technology. Boeing
Aeromagazine. Retrieved from: http://www.boeing.com/commercial/aeromagazine/articles/qtr_02_10/pdfs/AERO_Q2-10_article02.pdf
Rosenkrans, W. (2014,
October). ACAS X. AeroSafety World Magazine. Retrieved from: http://flightsafety.org/aerosafety-world-magazine/october-2014/acas-x.
Wyne, S. (2015).
Collision Avoidance in Unmanned Aerial Systems. Embry-Riddle Aeronautical
University, Unmanned Systems 610.
