DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0991; Project Identifier AD-2020-00478-Q;
Amendment 39-21509; AD 2021-08-15]
RIN 2120-AA64

Airworthiness Directives; Garmin International GMN-00962 GTS
Processor Units

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
certain Garmin International (Garmin) GMN-00962 GTS processor units
(GTS 825, GTS 855, GTS 8000). This AD was prompted by reports of GTS
processor units issuing resolution advisories (RAs) when no risk of
collision or loss of separation exists between the airplanes involved.
This AD requires updating the software version of the affected GTS
Processor units. The FAA is issuing this AD to address the unsafe
condition on these products.

DATES: This AD is effective May 17, 2021.

ADDRESSES: For service information identified in this final rule,
contact Garmin International, Garmin Aviation Support 1200 E. 151st
Street, Olathe, KS 66062; phone: (866) 739-5687; website: https://fly.
garmin.com/fly-garmin/support/. You may view this service
information at the FAA, Airworthiness Products Section, Operational
Safety Branch, 901 Locust St., Kansas City, MO 64106. For information
on the availability of this material at the FAA, call (816) 329-4148.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2020-0991; or in person at
Docket Operations between 9 a.m. and 5 p.m., Monday through Friday,
except Federal holidays. The AD docket contains this final rule, any
comments received, and other information. The address for Docket
Operations is U.S. Department of Transportation, Docket Operations, M-
30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue
SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Paul Rau, Aviation Safety Engineer,
Wichita ACO Branch, FAA, 1801 Airport Road, Wichita, KS 67209; phone:
(316) 946-4149; fax: (316) 946-4107; email: paul.rau@faa.gov or
Wichita-COS@faa.gov.

SUPPLEMENTARY INFORMATION:

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 by adding an AD that would apply to Garmin GMN-00962 GTS
processor units (GTS 825, GTS 855, GTS 8000) with part number 011-
02571-0( ) and software version 3.13 or earlier (except version
3.12.1). The NPRM published in the Federal Register on December 14,
2020 (85 FR 80696). The NPRM was prompted by seven reports of false RAs
involving aircraft equipped with Garmin GMN-00962 GTS processor
configured for traffic collision avoidance system II (TCAS II)
(configuration marketed as GTS-8000 units). The Garmin GMN-00962 GTS
processor units are marketed by Garmin as the GTS 825, GTS 855 or GTS
8000, with the marketing name representing the traffic system
configuration.
A false RA occurs when there is no risk of collision or loss of
separation of the airplanes. These false RAs result from the GTS
Processor software potentially calculating incorrect range rates. This
results in traffic advisories or RAs being generated when targets are
greater than 10 nautical miles (NM) away. A TCAS event involving three
or more airplanes can result in mid-air collision by increasing the
risk that the TCAS, in resolving the false RA with the initial
airplane, will create an actual loss of separation with a third
airplane. This condition, if not addressed, could result in an RA being
generated when no risk of loss of separation or risk of collision
exists between the airplanes involved, which can lead to a mid-air
collision with a third airplane.
In the NPRM, the FAA proposed to require updating the GTS processor
unit software. The FAA is issuing this AD to address the unsafe
condition on these products.
The affected GTS processor units were installed on the airplanes
listed below during production and via an STC; however, the affected
units may have been installed on other airplane models as a
supplemental type certificate (STC). Although the names found in
parenthesis may not be listed on the type certificate, the manufacturer
may use those names as marketing names for the airplanes.
Textron Aviation Inc. (type certificate previously held by
Cessna Aircraft Company) Model 525 (Cessna Citation M2), Model 525B
(Cessna Citation CJ3+), Model Model 680 Sovereign, Model 680A Latitude,
and Model 700 (Cessna Citation Longitude);
Embraer S.A. Model EMB-500 (Phenom 100) and Model EMB-505
(Phenom 300);
Learjet Inc. Model 45 (Learjet 70) and Model 45 (Learjet
75); and
Viking Air Limited (type certificate previously held by
Shorts Brothers PLC, Shorts Brothers Limited) Model SD3-60 SHERPA,
modified by Field Aerospace STC No. ST00865DE.

Discussion of Final Airworthiness Directive Comments

The FAA received comments from six commenters. The commenters were
Garmin, Learjet Inc. (Learjet), Textron Aviation Inc. (Textron),
NetJets, Field Aerospace, and an individual. The following presents the
comments received on the NPRM and the FAA's response to each comment.

Supportive

An individual commenter supported the NPRM without change.

Request Regarding Applicability

Garmin requested the FAA clarify the AD applicability, as the
proposed AD applies to GTS 825 and GTS 855, which are not affected by
the false RA issue. Garmin suggested that the FAA add a clarifying
statement to the background section, and revise the applicability
paragraph to remove references to the GTS 825 and GTS 855.
The FAA disagrees. This AD applies to the GTS Processor part number
011-02571-0( ) units with software version 3.13 or earlier, except
software version 3.12.1. The GTS 825, GTS 855, and GTS 8000 marketing
labels describe different installation configurations rather than
different appliances. While the GTS Processor will not generate false
RAs when configured as TAS (GTS 825) or TCAS I (GTS 855), the appliance
itself is still susceptible to the issue, and the unsafe condition
would occur if an operator enables the TCAS II option without also
updating the software.
The FAA did not change this AD based on this comment.

Request Regarding Affected Aircraft

Field Aerospace stated that the proposed AD would affect Shorts
Sherpa Model SD3-60 airplanes that have been modified under Field
Aerospace STC No. ST00865DE.
The FAA agrees with this comment. The FAA issued this AD against
the Garmin appliance because the unsafe condition exists in the
appliance. The FAA has added Model SD3-60 SHERPA airplanes modified by
Field Aerospace STC No. ST00865DE to the list of known affected
aircraft in the background section. This is not an all-inclusive list;
all operators must check their airplanes for the affected appliance,
regardless of whether the model of their airplane is listed.

Request Regarding Unsafe Condition

Garmin requested the FAA add information relevant to the actual
risk in the discussion of the unsafe condition in the background
section. Specifically, Garmin stated that loss of separation with a
third airplane is not inevitable when a false RA occurs. Garmin further
stated that the TCAS II implemented by the GTS 8000 is capable of
negotiating threats with more than one airplane and will adjust the RA
in a situation should loss of separation to a third airplane result in
a collision threat.
The FAA disagrees. The unsafe condition statement describes the
condition the FAA is trying to prevent; as such, it does not describe
all possible outcomes. The FAA assessed the likelihood of the unsafe
condition in determining whether an AD or other action was warranted.
While the FAA acknowledges that no loss of separation event has been
associated with this issue on Garmin equipment, a similar issue with
other TCAS II equipment has resulted in loss of separation events.
Additionally, the rate of false RAs observed with GTS Processor-
equipped aircraft far exceeds the acceptable probability of a false RA
due to a failure of the system specified in Advisory Circular No. 20-
151C, Airworthiness Approval of Traffic Alert and Collision Avoidance
Systems (TCAS II), Versions 7.0 & 7.1 and Associated Mode S
Transponders, dated July 21, 2017. Further, the potential for a loss of
separation is not limited to the GTS Processor-equipped aircraft, as
the second aircraft may also contain equipment that attempts to resolve
the multi-threat encounter. Although the TCAS II is capable of
resolving conflicts with more than one aircraft, since the current
design of TCAS RAs is limited to vertical maneuvers, it is not able to
provide conflict resolution for all encounters involving multiple
aircraft.
The FAA did not change this AD based on this comment.

Request Regarding Required Actions and Compliance

Garmin requested the FAA revise the AD to require updating the
affected software to version 3.12.1, or to version 3.14 or later.
Garmin stated that, as proposed, the AD would not allow update of
software to version 3.12.1, which is not affected by the issue.
The FAA agrees with this comment. The unsafe condition is also
resolved in version 3.12.1. The FAA has changed the Required Actions
and Compliance paragraph to also allow updating the GTS processor
software to version 3.12.1.
Learjet, Textron, and NetJets requested the FAA extend the
compliance time to allow adequate time for the certification and
deployment of the required changes to all affected products. Learjet
requested a compliance time of 18 months, while Textron requested a
compliance time of 24 months.
The FAA agrees. In addition to the reasons provided by the
commenters, the FAA's risk assessment, in consideration of the ongoing
pandemic and resulting reduction in air traffic,
supports extending the compliance time from 12 to 24 months.

Request Regarding Costs

Textron requested the FAA update the estimated cost information to
include additional work for Textron aircraft. Textron stated it has
prior agreements with Garmin to accomplish this software change as part
of a package of other product improvements, for a per-aircraft cost of
approximately $3,000.
The FAA disagrees with this comment. The cost analysis in AD
rulemaking actions typically includes only the costs associated with
complying with the AD. This AD does not mandate the entire package of
changes for Textron aircraft.
The FAA has not made changes to this AD based on this comment.

Request Regarding Certificate of Airworthiness

Learjet requested the FAA revise the AD to allow initial
Certificates of Airworthiness to be issued to newly-manufactured
aircraft prior to complying with the AD. Learjet stated that
certification of new software to comply with the AD (software later
than version 3.13) will take a minimum of 9 months.
The FAA disagrees with this comment. The AD does not prohibit the
issuance of a Certificate of Airworthiness to eligible aircraft. Newly-
manufactured aircraft need to comply with the AD actions within the
same timeframe as aircraft in the current U.S. fleet.
The FAA has not made changes to this AD based on this comment.

Conclusion

The FAA reviewed the relevant data, considered any comments
received, and determined that air safety requires adopting this AD as
proposed. Accordingly, the FAA is issuing this AD to address the unsafe
condition on these products. Except for minor editorial changes and any
other changes described previously, this AD is adopted as proposed in
the NPRM. None of the changes will increase the economic burden on any
operator.

Related Service Information

The FAA reviewed Garmin Service Bulletin No. 2065, Revision A,
dated May 7, 2020; and Garmin Service Bulletin No. 1948, Revision B,
dated March 26, 2020. These service bulletins contain procedures for
uploading the software update to the GMN-00962 GTS Processor units (GTS
825, GTS 855, GTS 8000).

Costs of Compliance

The FAA estimates that this AD affects 700 appliances installed on
airplanes of U.S. registry.
The FAA estimates the following costs to comply with this AD:

Estimated Costs

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. Subtitle VII: Aviation Programs,
describes in more detail the scope of the Agency's authority.
The FAA is issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701: General requirements.
Under that section, Congress charges the FAA with promoting safe flight
of civil aircraft in air commerce by prescribing regulations for
practices, methods, and procedures the Administrator finds necessary
for safety in air commerce. This regulation is within the scope of that
authority because it addresses an unsafe condition that is likely to
exist or develop on products identified in this rulemaking action.

Regulatory Findings

This AD will not have federalism implications under Executive Order
13132. This AD will not have a substantial direct effect on the States,
on the relationship between the national government and the States, or
on the distribution of power and responsibilities among the various
levels of government.
For the reasons discussed above, I certify that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Will not affect intrastate aviation in Alaska, and
(3) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.

The Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. The FAA amends Sec. 39.13 by adding the following new airworthiness
directive: