Monitoring the Sovereign Skies

Monitoring the Sovereign Skies

INSIGHTi

Monitoring the Sovereign Skies
February 27, 2023
In early 2023, a high-altitude balloon that originated in China transited through U.S. airspace before being
shot down by military aircraft off the coast of South Carolina. Soon after, the U.S. military identified,
tracked, and, under presidential orders, destroyed three additional unidentified flying objects in Alaska,
Canada, and over Lake Huron. Little has been revealed about these incidents, but President Biden noted
that the three objects may have been operated by private entities or research organizations and are not
believed to have posed a national security threat. However, Biden Administration officials, including
Secretary of Defense Lloyd Austin, expressed concern that the unpiloted flying objects that were shot
down, besides being unauthorized, posed risks to civil aviation.
These events have raised questions about flight authorizations and tracking of manned and unmanned
aircraft in U.S. airspace. Although Federal Aviation Administration (FAA) air traffic controllers actively
monitor most piloted flights operating within U.S. airspace, not all aircraft are required to file flight plans,
and many cannot be uniquely identified or tracked.
Sovereignty of Airspace
The United States asserts sovereignty of the airspace overlying the United States and its territories. Each
country’s sovereign right to control airspace, above its lands and territorial waters, up to the ill-defined
boundary of space, is formally recognized by the International Civil Aviation Organization’s (ICAO’s)
Convention on International Civil Aviation. Article 5 of the convention generally grants foreign-registered
civil aircraft not engaged in scheduled air service access to airspace of a foreign country, whereas
international air service must be formally agreed to and authorized. Foreign aircraft are generally
permitted to transit through U.S. airspace and operate to and from U.S. airports but must follow specific
national security procedures and airspace and customs regulations. Article 8 of the ICAO convention
specifically states that aircraft without pilots on board flown over another country must obtain special
permission from that country and must be “controlled as to obviate danger to civil aircraft.”
Aircraft Identification and Tracking
During peak times, more than 5,000 aircraft are under active FAA air traffic control. Every day, more than
45,000 flights transit the 29 million square miles of airspace managed by FAA, including over 5 million
square miles of domestic airspace overlying the contiguous United States and Alaska. FAA has
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technologies, regulations, and procedures for identifying and tracking these aircraft, including airships,
balloons, and drones. Capabilities for tracking and identifying aircraft include
 primary radar returns, which are reflections of radar signals from ground-based radar
antennas that “bounce back” off aircraft fuselages and other reflective surfaces;
 secondary radar, which relies on a transponder signal from equipped aircraft, emitted in
reply to interrogation signals from ground-based radar beacons; and
 Automatic Dependent Surveillance – Broadcast (ADS-B), which continuously transmits
identification and location signals from equipped aircraft.
FAA requires powered aircraft operating in certain areas—including all airspace above 18,000 feet, most
airspace above 10,000 feet, and airspace around busy airports—to be equipped with ADS-B, which
typically relies on the Global Positioning System (GPS) to provide aircraft location data. Similar
regulations exist for powered aircraft to have radar transponders in these areas.
All flights operating under instrument flight rules (IFR) must file flight plans with FAA. For operations
within the boundaries of U.S. airspace, most aircraft operating under visual flight rules (VFR) are not
required to have flight plans but may voluntarily do so. IFR flights are assigned unique transponder codes
for identification. VFR flights generally do not transmit unique transponder codes but must set
transponders to a generic VFR code and activate ADS-B if so equipped. VFR flights must establish two-
way radio communications with air traffic control and receive clearance to fly at or above 18,000 or near
busy towered airports. Airspace above 60,000 feet is not controlled, but flights must obtain clearances or
authorizations to transit through controlled airspace to reach these rarified heights.
Unmanned Balloons
Untethered, unmanned free balloons that exceed minimum size criteria cannot be launched unless the
operator provides advance notice to the nearest FAA facility, monitors the balloon’s position at least every
two hours, and forwards tracking information to air traffic control upon request. Operators must also give
notice prior to initiating descent, providing the balloon’s position, altitude, and trajectory for the
remainder of the flight. Unmanned balloons must have radar reflective devices or materials and, if
operated at night, must have flashing lights visible for at least 5 miles. They are not required to have
transponders or ADS-B.
Other Unmanned Aircraft
By September 16, 2023, drones that weigh under 55 pounds, whose operations are mostly restricted to
airspace below 400 feet, will be required to be equipped with remote identification capabilities.
Exceptions will be allowed in certain FAA-recognized identification areas, such as recreational airparks.
Generally, aircraft subject to these regulations have relatively limited ranges, payloads, and altitude
capabilities. Larger drones and unmanned vehicles operated at higher altitudes are not always tracked but
do require specific FAA authorization.
Air Defense Identification Zones and Airspace Restrictions
The United States maintains Air Defense Identification Zones (ADIZs) extending beyond the sea borders
of the contiguous states and around Alaska, Hawaii, and Guam. Canada also maintains an ADIZ
extending from its shores and its arctic borders. Monitoring and enforcement of ADIZ procedures are the
responsibility of the North American Aerospace Defense Command (NORAD), a binational U.S. and
Canadian military organization. All powered aircraft must activate a flight plan and use transponders
when operating in the ADIZ. Pilots must provide position reports prior to penetrating the ADIZ and when

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operating within it. Inside U.S. airspace, FAA maintains a special flight rules area (SFRA) around
Washington, DC, that requires authorization and special operating procedures. Additionally, various other
airspace restrictions have been implemented, including around stadiums, Disney theme parks, security
sensitive sites, military ranges, and in various locations on a temporary basis for presidential visits,
natural disasters, emergency response, and other purposes.

Author Information

Bart Elias

Specialist in Aviation Policy

Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff
to congressional committees and Members of Congress. It operates solely at the behest of and under the direction of
Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of
information that has been provided by CRS to Members of Congress in connection with CRS’s institutional role.
CRS Reports, as a work of the United States Government, are not subject to copyright protection in the United
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