Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
2022-16
August 17, 2022
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin advises manufacturers
and operators of an airworthiness concern about lack of traffic
conflict alerting or collision detection functionality for their
Automatic Dependent Surveillance - Broadcast (ADS-B) In Systems.
At this time, the FAA has determined that the airworthiness concern is
not an unsafe condition that would warrant Airworthiness Directive (AD)
action under Title 14 of the Code of Federal Regulations (14 CFR) part
39.
Background
On May 13, 2019 in Ketchikan, AK, a float-equipped de Havilland DHC-2
(Beaver) airplane, N952DB, and a float-equipped de Havilland DHC-3
(Otter) airplane, N959PA, collided midair. The DHC-2 pilot and four
passengers sustained fatal injuries. The DHC-3 pilot sustained minor
injuries, nine passengers sustained serious injuries, and one passenger
sustained fatal injuries. The DHC-2 was destroyed and the DHC-3
sustained substantial damage. Both aircraft were equipped with ADS-B
Out and In. The FAA Safety Issue Action Team reviewed the investigation
findings documented in National Transportation Safety Board (NTSB)
Accident No. CEN19MA141 as well as information from other recent midair
collisions.
NTSB Accident No. CEN19MA141 findings revealed that one aircraft had a
Technical Standard Order (TSO)-C195a ADS-B In system installed, but
that aircraft’s ADS-B In unit did not have collision alerting or
collision detection functionality because TSO-C195a had no requirements
or standards for such functionality. As a result of the lack of
conflict alerting functionality, the ADS-B In system had no means of
providing an aural alert to the pilot to warn of the impending conflict.
The Minimum Operational Performance Standards (MOPS) in the current
ADS-B In TSO-C195b, RTCA document DO-317B, and the subsequent MOPS
revision, RTCA DO-317C, now provide standards for an ADS-B In conflict
alerting application called ADS-B Traffic Advisory System (ATAS) in
TSO-C195b. In addition to visual conflict alerting, ATAS provides voice
aural alerts of impending conflicts consisting of the word “Traffic”
along with information on relative bearing (expressed as a “clock
position”) and usually relative altitude (“high”, “low” etc.), range,
and vertical tendency (e.g. “descending”). ATAS may also be implemented
without a traffic display. However, ATAS is an optional application for
a TSO-C195b system, and is also currently an optional application in
DO-317C.
A report related to NTSB Accident No. CEN19MA141 analyzed the
performance of the ADS-B In systems on the two aircraft and concluded,
“… the circumstances of this accident indicate that pilots might not
always use Cockpit Display of Traffic Information consistently to
supplement their visual scan for traffic, and that aural alerts that
draw the pilot’s attention to imminent traffic threats can
significantly improve the effectiveness of these systems.” NTSB studies
of several recent midair collisions, including Accident No. CEN19MA141,
have further concluded that had the accident
aircraft been equipped with ADS-B Out and a TSO-C195b system with ATAS,
the ADS-B In system would have provided significant advance warning of
the collision. In most cases, this warning would be between 20 and 39
seconds in advance.
Recommendations
The FAA recommends that
manufacturers of ADS-B In systems ensure their systems meet the
performance requirements of TSO-C195b or later revision, and include
the ATAS application or equivalent traffic conflict alerting capability.
The FAA recommends that
operators performing an initial installation of an ADS-B In system in
their aircraft install a system that meets the performance requirements
of TSO-C195b or later revision, that incorporates ATAS or equivalent
traffic conflict alerting capability.
The FAA recommends that
operators with existing ADS-B In equipment installations prior to
TSO-C195b, or with an existing TSO-C195b installation without ATAS,
upgrade to a system meeting the performance requirements of TSO-C195b
or later revision, that incorporates ATAS or equivalent traffic
conflict alerting capability.
For Further Information Contact
Ray Mei, Aviation Safety Engineer, Aircraft Information Systems
Section, FAA, 2200 South 216th Street, Des Moines, WA 98198; phone:
(206) 231-3541; email: raymont.mei@faa.gov