Avionics News May 2017 - 16

INTERNATIONAL NEWS
Continued from page 15

FREQUENTLY ASKED
QUESTIONS: ADS-B

ADS-B Out systems
air-ground
considerations
The following information is from the
Federal Aviation Administration
Advisory Circular 20-165.

QUESTION:

What considerations should the installer be
aware of regarding the air-ground status of
ADS-B Out systems?

ANSWER:

FAA Advisory Circular 20-165B paragraph
3.10 contains the procedures for air-ground
considerations.
According to the AC:
The length and width code is required
by § 91.227, and is only transmitted in
the surface position message. Thus, to
comply with the rule, the aircraft must
automatically determine its air-ground
status and transmit the surface position
message, which includes the length and
width code, when on the ground.
For aircraft with retractable landing gear,
the air-ground status determination is
typically provided through a landing gear
weight-on-wheels switch.
For aircraft that have fixed gear, the
ADS-B system must still be able to
determine the air-ground status of the
aircraft. Installations that provide a

16

avionics news

*

may

2017

means to automatically determine airground status based on inputs from other
aircraft sensors may be acceptable if they
can be demonstrated to accurately detect
the status. For example, air-ground status
may be derived from WOW switch and
GPS velocity; or GPS velocity, an airport
database, and geometric altitude; or GPS
velocity and airspeed. These algorithms
should be tested and validated during the
installation approval.
Note 1: We (the FAA) recommend that
any automatic air-ground determination
be more robust than just a simple
comparison of ground speed to a single
threshold value. Field experience has
shown that this method can lead to false
air-ground status.
Note 2: Manual selection of the airground status is not acceptable.
Note 3: Rotorcraft may require unique
logic for providing an accurate air-ground
state. A reliable method to determine the
air-ground state should consider training
requirements. Rotorcraft may consider
hover taxi as in the air.
It is important for the installer to know
and understand how the specific equipment
manufacturer has achieved the air-ground
status to properly advise the customer on the
operation of the installed system. q



Table of Contents for the Digital Edition of Avionics News May 2017

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Avionics News May 2017 - Intro
Avionics News May 2017 - No label
Avionics News May 2017 - Cover2
Avionics News May 2017 - 1
Avionics News May 2017 - 2
Avionics News May 2017 - 3
Avionics News May 2017 - 4
Avionics News May 2017 - 5
Avionics News May 2017 - 6
Avionics News May 2017 - 7
Avionics News May 2017 - 8
Avionics News May 2017 - 9
Avionics News May 2017 - 13
Avionics News May 2017 - 11
Avionics News May 2017 - 12
Avionics News May 2017 - 13
Avionics News May 2017 - 14
Avionics News May 2017 - 15
Avionics News May 2017 - 16
Avionics News May 2017 - 17
Avionics News May 2017 - 18
Avionics News May 2017 - 19
Avionics News May 2017 - 20
Avionics News May 2017 - 21
Avionics News May 2017 - 22
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Avionics News May 2017 - 26
Avionics News May 2017 - 27
Avionics News May 2017 - 28
Avionics News May 2017 - 29
Avionics News May 2017 - 30
Avionics News May 2017 - 31
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Avionics News May 2017 - 70
Avionics News May 2017 - 71
Avionics News May 2017 - 72
Avionics News May 2017 - Cover3
Avionics News May 2017 - Cover4
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