Aerospace & Defense Technology - May 2021 - 18

Does Your
UAV Program
Need a Transponder?
Understanding the
Requirements and Guidelines

ith the continuous growth
of the unmanned aircraft
industry, and the anticipated trajectory to come
with urban air mobility solutions, commercial civil applications, and more,
suppliers are often asked, " Does my UAS
need a transponder? " Vehicle designers
need to understand the current and anticipated requirements to make an informed decision on incorporating
transponders into an aircraft.

The Standards Today
In a word, the standards today are
" emerging. " There is no single chart
from any global agency that sums up
the requirements for transponders on
unmanned aircraft of all types, for all

classes of airspace, in all geographies.
Therefore, this article brings together
the current best practices and knowledge from around the industry to serve
as a reference for unmanned aerial systems and vehicles that are above 55
pounds and operating under 14 CFR 91
( " Part 91 " ) aviation requirements.

Does An Unmanned Aircraft Need A
Transponder?
An aeronautical transponder is an electronic device that produces a response
when it receives a radio-frequency interrogation. Transponders provide vital information to Air Traffic Control (ATC)
and other aircraft's Airborne Collision
Avoidance Systems (ACAS or TCAS). Collision avoidance systems use transponder

UAS
Group

Maximum
Nominal
Weight (lb.) Operating
(MTOW)
Altitude (ft)

Speed
(kn)

Representative UAS

Group 1

0-20

< 1,200 AGL

100

RQ-11, Raven, WASP

Group 2

21-55

< 3,5000 AGL

< 250

ScanEagle, Flexrotor,
SIC5

Group 3

< 1,320

< < FL 180

< 250

V-BAT, RQ-7B Shadow,
RQ-21 Blackjack, Navmar
RQ-23 Tigershark,
Arturus - UAV Jump 20,
Arcturus T-20, AATI
Resolute Eagles, SIC25

Group 4

> 1,320

< FL 180

Any
MQ-8B Fire Scout,MQairspeed 1A/B Preditor, MQ-1C Gray
Eagle

Group 5

> 1,320

< FL 180

Any
MQ-9Reaper, RQ-4 Global
airspeed Hawk, MQ-4C Triton

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Cov

ToC

transmissions as a means of detecting aircraft at risk of colliding with each other.
The transponder receives interrogations
from ground-based secondary surveillance radars and ACAS systems on 1030
MHz and replies on 1090 MHz.
Additionally, ADS-B Out was made a
requirement on all aircraft flying in
most controlled airspace. According to
the FAA, " Real-time precision, shared
situational awareness, advanced applications for pilots and controllers alike -
these are the hallmarks of ADS-B
NextGen surveillance. Real-time ADS-B
is now the preferred method of surveillance for air traffic control in the National Airspace System (NAS). " Advanced transponders today offer these
technologies, ideally integrated into a
single electronic device, to satisfy aircraft airworthiness requirements.
In answer to the question, " Does a
UAS need a transponder, " the short answer is " It depends. " A mix of mission
parameters and airspace requirements
plays into a transponder decision:
1. How big is the aircraft? Typically,
aircraft that need to fly in controlled
airspace are of significant size and
weight, usually more than 55 pounds.
Smaller aircraft, perhaps down to 20
pounds, may also operate under Part
91 rules if they are flying beyond visual
line of sight (BVLOS) in National Airspace, above 400 feet AGL. The U.S.
Department of Defense classifies UAS
into five groups, shown in the chart,
with each category increasing in capability. Civil UAS that align with groups
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