DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2016-9226; Directorate Identifier 2016-SW-065-AD;
Amendment 39-18910; AD 2017-11-11]
RIN 2120-AA64

Airworthiness Directives; NavWorx, Inc. Automatic Dependent
Surveillance Broadcast Universal Access Transceiver Units

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: We are adopting a new airworthiness directive (AD) for
NavWorx, Inc. (NavWorx), Automatic Dependent Surveillance Broadcast
(ADS-B) Universal Access Transceiver Units (unit). This AD requires
removing, disabling, or modifying the ADS-B unit. This AD was prompted
by a design change that results in the unit communicating unreliable
position information. The actions in this AD are intended to address an
unsafe condition on these products.

DATES: This AD is effective July 11, 2017.

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov
by searching for and locating Docket No. FAA-2016-9226;
or in person at the Docket Operations Office between 9 a.m. and 5
p.m., Monday through Friday, except Federal holidays. The AD docket
contains this AD, Supplemental Type Certificate (STC) No. SA11172SC,
the economic evaluation, any comments received, and other information.
The street address for the Docket Operations Office (phone: 800-647-
5527) is U.S. Department of Transportation, Docket Operations Office,
M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue
SE., Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Kyle Cobble, Aviation Safety Engineer,
Fort Worth Aircraft Certification Office (ACO), Rotorcraft Directorate,
FAA, 10101 Hillwood Pkwy, Fort Worth, TX 76177, telephone (817) 222-
5172, email kyle.cobble@faa.gov; or Michael Heusser, Program Manager,
Continued Operational Safety Branch, Fort Worth ACO, Rotorcraft
Directorate, FAA, 10101 Hillwood Pkwy, Fort Worth, TX 76177, telephone
(817) 222-5038, email michael.a.heusser@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

On October 20, 2016, at 81 FR 72552, the Federal Register published
our notice of proposed rulemaking (NPRM), which proposed to amend 14
CFR part 39 by adding an AD that would apply to NavWorx ADS-B Model
ADS600-B units, part number (P/N) 200-0012 and P/N 200-0013, and Model
ADS600-EXP units, P/N 200-8013. The NPRM proposed to require removing
the ADS-B unit before further flight and proposed to prohibit
installing the affected ADS-B unit on any aircraft. The NPRM was
prompted by a design change that resulted in the ADS-B units
broadcasting a Source Integrity Level (SIL) of 3 instead of 0. A
broadcast of SIL 0 is required because of the uncertified Global
Positioning System (GPS) source included in the unit. The proposed
actions were intended to prevent an ADS-B unit from communicating
unreliable position information to Air Traffic Control (ATC) and nearby
aircraft and a subsequent aircraft collision.

Comments

We gave the public the opportunity to participate in developing
this AD. We received approximately 200 comments, mostly from
individuals but also from NavWorx and organizations such as the
Aircraft Owners and Pilots Association (AOPA), the Experimental
Aircraft Association (EAA), and the Aircraft Electronics Association
(AEA). The following presents the comments received on the NPRM and the
FAA's response to each comment.

A. Support for the NPRM

Five individual commenters supported the NPRM.

B. Comments Regarding the FAA's Justification of the Unsafe Condition

Several commenters, including AOPA, requested that the FAA provide
more information about the events that prompted this AD and the
technical aspects surrounding the unsafe condition. We agree.
Request: AOPA requested the FAA clarify whether the internal
position source in the ADS-B units meets the performance requirements
in Appendix B to Advisory Circular (AC) 20-165B. In support of this
request, AOPA stated the FAA's contention that NavWorx did not present
any data substantiating its SIL change is contrary to NavWorx's public
statements that its testing verified the position source met the
integrity levels required by the regulations. Similarly, NavWorx
commented on the AD and maintained it has provided the FAA with data
demonstrating the internal GPS met the requirements to transmit a SIL
of 3.
FAA Response: NavWorx has not demonstrated to the FAA that the
internal position source meets the performance requirements in Appendix
B to AC 20-165B \1\ for a SIL of 3. The design specifications for
NavWorx's P/N 200-0012 and 200-0013 ADS-B units identify the internal
GPS source for those units as an uncertified SiRF IV GPS. The SiRF IV
is a commercial grade chipset not manufactured under an FAA Technical
Standard Order (TSO). AC 20-165B requires the SIL be set at 0 when the
ADS-B is integrated with an uncertified GPS source. When NavWorx
submitted its software upgrade changing the SIL value from 0 to 3, no
hardware design changes associated with the SIL value change were made
to the ADS-B units and no testing data substantiating that SIL change
was provided to the FAA. The only justification NavWorx cited for the
software change was the FAA's termination of Traffic Information
Service--Broadcast (TIS-B) services to aircraft broadcasting ADS-B with
a SIL of 0. This data is available for review in Docket No. FAA-2016-9226.
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Request: AOPA requested the FAA clarify its meaning of
``uncertified GPS source'' since NavWorx has design approval through
STC No. SA11172SC to install the ADS-B unit with the internal GPS on
type-certificated aircraft, and since a compliant position source does
not need to meet a specific TSO to meet the requirements set forth in
Appendix B of AC 20-165B.
Some commenters requested the FAA explain why it approved NavWorx's
ADS-B units at all if the internal, uncertified GPS source is
objectionable. Many commenters stated the NavWorx ADS-B units meet the
performance and accuracy/integrity standards of TSO C-154c; others
noted that NavWorx has stated its testing showed the units meet the
requirements to broadcast a SIL of

3. Several commenters disagreed with the AD because the GPS source is
not required to be certified separately from the ADS-B unit.
FAA Response: The commenters, including NavWorx, are correct that
the position source only needs to meet certain performance requirements
and does not need to be certified under a TSO. However, despite
NavWorx's statements and comments to the contrary, NavWorx has
presented no data to the FAA--test plans and test results--that
demonstrate the affected units with the internal SiRF IV GPS meet the
performance standards to transmit a SIL of 3. Similarly, NavWorx has
never demonstrated to the FAA that the affected units meet the 14 CFR
Sec. 91.227 requirements to broadcast a SIL of 3 when using the
internal SiRF IV GPS.
NavWorx's TSO-C154c authorization and STC were approved based on
the P/N 200-0012 and 200-0013 units broadcasting a SIL of 0 when using
the internal uncertified GPS position source. NavWorx documented this
as a limitation in the Aircraft Flight Manual Supplement (AFMS) for
NavWorx's STC for ADS600-B installations. Section 2.6 of the AFMS,
titled ``Uncertified GPS Receiver (P/N 200-0012 and 200-0013),''
states:

The ADS600-B has an internal uncertified GPS WAAS receiver which
does not meet the 14 CFR 91 FAA-2007-29305 rule for certified GPS
position source. If the ADS600-B is configured to use the internal
uncertified GPS as the position source the ADS-B messages
transmitted by the unit reports: A Source Integrity Limit (SIL) of 0
indicating that the GPS position source does not meet the 14 CFR 91
FAA-2007-29305 rule.

While 14 CFR Sec. 91.227 requires a SIL of 3, TSO-C154c (the TSO
under which the affected units are produced) does not. Thus, when the
affected units broadcast a SIL of 0, they are TSO-compliant. Until the
performance requirements of 14 CFR Sec. 91.227 become effective on
January 1, 2020, the FAA does not find the internal uncertified GPS
source objectionable, as long as the ADS-B unit is correctly
broadcasting a SIL of 0. It is NavWorx's change of the SIL setting in
these units to 3, without any qualification of the internal uncertified
GPS position source to support broadcast of SIL 3, that the FAA finds
unacceptable. In this condition, the units are transmitting to ATC and
to nearby aircraft that they have 14 CFR Sec. 91.227-compliant
position source integrity, when their position source integrity is
actually not compliant with that rule, or is unknown. We discuss the
safety effects of this condition in greater detail below.
Request: AOPA requested the FAA further explain its finding that
the affected units create an unsafe condition. Many commenters
questioned the FAA's determination that the units present an unsafe
condition, and asked whether any units have actually caused a collision
or safety incident. Many other commenters stated they have been
operating with the NavWorx unit and find it accurate and reliable.
Several commenters stated the NavWorx units increase safety and noted
that the National Transportation Safety Board has recommended ADS-B
units to the flying public.
FAA Response: The FAA's safety concern is primarily that of
integrity, and not necessarily accuracy, with respect to the NavWorx
ADS-B unit's performance requirements. Accuracy refers to the
probability of the unit's true position in relation to its reported
position.\2\ Integrity refers to the trust that can be placed in the
correctness of the information provided by the unit and is specified by
a SIL value. The SIL value is set based on design data from the GPS
position source manufacturer and reflects the probability that the
position source will provide incorrect data without providing an alert.
This depends on whether the GPS has fault detection and exclusion,
where the equipment will detect a faulty satellite and exclude it from
the navigational calculations. If the GPS does not have fault detection
and exclusion, the probability that the position source will provide
incorrect data increases. Commercial position sources, such as the SiRF
IV GPS used in the NavWorx P/N 200-0012, 200-0013, and 200-8013 units,
do not have fault detection and exclusion capabilities. This is
significant in the event a GPS satellite signal fails or a GPS
``signal-in-space error'' occurs.
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\2\ Accuracy of an aircraft's reported position is specified as
Navigation Accuracy Category for Position, or NACP. A
unit that complies with 14 CFR 91.227 has a NACP
corresponding to an accuracy of better than 0.05 nautical miles. The
NavWorx units' compliance with the 14 CFR 91.227 NACP (accuracy)
performance requirements is not the concern that prompted this AD.
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The unsafe condition relates to the potential for the NavWorx unit
to incorrectly report its own position to other aircraft and to ATC, by
0.2 nautical miles (NM) or more, without providing an alert.\3\ It may
also result in ATC providing incorrect and inappropriate separation
instructions or traffic advisories to other aircraft for avoidance of
the ADS600-B-equipped aircraft, based on the erroneous position being
reported by the ADS600-B. In this situation, the pilot of the ADS600-B-
equipped aircraft would be unaware that his or her aircraft's ADS-B Out
unit is broadcasting an erroneous position (possibly in excess of 0.2
NM), since the ADS600-B would not be providing an alert for this
condition. Depending on operating conditions, these effects may occur
in instrument meteorological conditions where see-and-avoid is not
possible. In view of these factors, this condition poses an
unacceptable hazard to other users of the National Airspace System
(NAS).
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\3\ 0.2 NM is the minimum integrity containment radius around
the aircraft's reported position required by 14 CFR Sec. 91.227
(c)(1)(iii).
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Although there have been no reported cases of a collision or safety
incident resulting from an incorrect transmission by a NavWorx ADS-B
unit to date, the potential for the unsafe condition exists as long as
the units mislead ATC and nearby aircraft by broadcasting a SIL of 3
that they have not been shown to meet. This AD action addresses that
potential unsafe condition.
The fact that commenters have made flight tests with satisfactory
ADS-B performance monitor reports from the FAA, or that commenters'
individual units have been operating successfully, does not negate the
existence of an unsafe condition. Flight tests with the ADS-B
performance monitor are designed primarily to show that the ADS-B
equipment in an individual aircraft performs correctly as installed.
These tests are of relatively short duration and occur in fault-free
conditions. They are not engineering tests designed to evaluate the
unit's ability to handle GPS signal-in-space errors and cannot be used
to draw inferences about the unit's position source integrity.
Although the FAA recognizes the benefits of ADS-B equipage and
understands that the NavWorx units may work a large percentage of the
time for an individual user, the FAA must consider the effect on the
entire NAS. Since failure is based on a statistical probability, the
odds that a unit will have a failure increase as more units are
introduced into the NAS and operate for a longer period of time. The
probability of a failure also increases when there is a GPS satellite
malfunction, which could affect many aircraft since the information is
used by ATC and ADS-B In equipped aircraft for separation. Therefore,
despite any benefit to individual owners when the unit works without
failure, the FAA has determined that an unsafe condition with the
NavWorx units exists and requires corrective action because of the
hazard they pose to other users of the NAS.

Request: AOPA requested the FAA produce for public inspection the
Small Airplane Risk Analysis (SARA) documentation.
FAA Response: As part of our risk assessment, we initially
performed a SARA. However, the SARA assumes failure on one airplane.
The issue with the NavWorx ADS-B units poses risk to the NAS.
Specifically, a malfunction at the satellite level could result in
transmission of hazardously misleading position information from the
ADS600-B-equipped aircraft to ATC and to other aircraft. It could also
cause such malfunctions in all aircraft with the affected ADS-B units
installed that are using the signal from the malfunctioning satellite
to determine their position. Thus, we determined the SARA results
provided questionable value, and that it was more appropriate to use
the safety risk methodology from the ADS-B program, as documented in
Safety Risk Management Document (SRMD) Critical Services: Standard
Terminal Automation Replacement System (STARS) with Automatic Dependent
Surveillance Broadcast (ADS-B) Only Addendum, SBS-036C, Revision 1,
dated August 26, 2014 (SBS-036C).
In SBS-036C, we analyze safety risk as a composite of two factors:
The potential ``severity'' or worst possible consequence or outcome of
an adverse effect that is assumed to occur, and the ``likelihood'' of
occurrence for that specific adverse event. We assess both factors
independently and then enter each as separate inputs into a risk
matrix, which yields an overall level of risk for the event as Low
(acceptable), Medium (acceptable with mitigation), or High
(unacceptable). The corrective action, if any, is driven by the
assessed overall risk. Figure ES-1 of SBS-036C contains the risk matrix
the FAA used for this AD.
The FAA considered an undetected position error event of 0.2 NM or
more for a single aircraft as a ``Position error outside containment
bound for single aircraft undetected by airborne equipment/ground
automation'' hazard, which has a classified severity of ``hazardous''
per Table ES-1 and Appendix B of SBS-036C. Hazardous is defined in AC
23.1309-1E, System Safety Analysis and Assessment for Part 23
Airplanes,\4\ as resulting in a large reduction in safety margins,
physical distress or higher workload, or serious or fatal injury to an
occupant other than the flight crew. A large position error (0.2 NM or
more) may lead to loss of separation, increased ATC workload, a
reduction in safety margins, and a near midair collision. These are
unsafe conditions that warrant a ``hazardous'' severity level for risk
assessment purposes.
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From Table ES-1 of SBS-036C, the likelihood of this failure for a
properly functioning system was assessed as extremely improbable.
Figure ES-1 in SBS-036C is a risk matrix that yields an overall risk
based on the severity classification and the assessed likelihood of
occurrence. A severity classification of ``hazardous'' and an assessed
likelihood of ``extremely improbable'' yields an overall risk of
``Low,'' which is an acceptable risk.
However, the likelihood assessment of ``extremely improbable'' in
Table ES-1 is based on the aircraft's GPS receiver having either fault
detection or fault detection and exclusion, which is required in order
to meet the ADS-B Out position integrity requirements of 14 CFR 91.227.
A GPS receiver with fault detection detects a faulty satellite signal
and provides an alert of the fault. If the GPS receiver has fault
detection and exclusion, it additionally excludes the faulty satellite
signal from the position computation. Because the GPS position source
in the NavWorx ADS600-B units has no demonstrated fault detection or
exclusion features, the FAA determined the appropriate likelihood
should be based on the GPS constellation fault rate of
10-\4\ per hour (that is, a probability of 0.0001
occurrences per flight hour). As a result, the FAA elevated the risk of
the hazard and assessed a likelihood of ``remote.'' \5\ Using the
severity classification of ``hazardous'' and an assessed likelihood of
``remote'' yields an overall risk of ``High'' in Figure ES-1. This is
an unacceptable risk.
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\5\ Although the CARB assessed a likelihood of ``remote,''
Figure 2 of AC 23.1309-1E assesses a likelihood between ``remote''
and ``probable,'' depending on the class of aircraft, for a
probability of 10\-4\. Either likelihood classification would yield
a High overall risk on the Figure ES-1 risk matrix.
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These determinations are documented in the meeting minutes from the
FAA's Corrective Action Review Board (CARB) held on September 19, 2016.
In accordance with FAA Order 8110.107A, Monitor Safety/Analyze Data,
the CARB considered this safety issue on that date and determined that
an unsafe condition existed with the units. This documentation is
available for review in Docket No. FAA-2016-9226.
Comment: A few commenters, including NavWorx, noted the FAA
approved software revisions 4.0.7, 4.0.8, and 4.0.9, which included the
software changes for the units to broadcast a SIL of 3.
FAA Response: The commenters are correct that the FAA approved
NavWorx's software changes identified as 4.0.7, 4.0.8, and 4.0.9.
However, none of these changes identified on NavWorx's submittals
affected the SIL value or referenced the SIL value change in 4.0.6. The
FAA's approvals did not alter the FAA's previous written statements to
NavWorx advising the equipment must report a SIL of 0 to remain
compliant with TSO-C154c. This documentation is available for review in
Docket No. FAA-2016-9226.

C. Requests To Allow Alternative Actions

Request: Many commenters, including AOPA, requested that, since the
internal GPS is the issue with the NavWorx unit, the AD allow the ADS-B
units to use an external GPS position source or, similarly, that the AD
not apply to units using an external GPS position source.
FAA Response: We agree. The only external GPS position source
approved by the FAA for interface with the ADS600-B is the Accord
NexNav mini LRU GPS Receiver P/N 21000 (Accord external GPS).\6\ We
revised the AD to allow interfacing the ADS-B unit with an Accord
external GPS as an optional corrective action. For operators who wish
to interface with other external position sources, under the provisions
of paragraph (f) of this AD, we will consider requests for approval of
an Alternative Method of Compliance (AMOC) if sufficient data is
submitted to substantiate that the unit would provide an acceptable
level of safety.
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\6\ Some commenters stated or implied that other external GPS
sources, such as the Garmin 530W, the Garmin GNS 430W, the Garmin
GNS 480, and the Garmin GTN 650, are approved for installation in
the ADS600-B. Contrary to any documentation these commenters may
have from NavWorx, the only FAA-approved external GPS source is the
Accord NexNav mini P/N 21000. Documentation of this is available for
review in Docket No. FAA-2016-9226.
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Request: Several commenters, including AEA, requested the AD allow
disabling the unit rather than removing it.
FAA Response: We agree. We revised the AD to allow disabling the
unit as an optional corrective action.
Request: Several commenters, including AOPA, requested the AD allow
changing the SIL from 3 to 0 as an alternative to removing the unit.
FAA Response: We agree. We did not include this option in the NPRM
because NavWorx has stated it will not provide its customers with
software to change the SIL to 0. However, we revised the AD to allow
changing the SIL to 0 as an alternative to removing the unit in the event such
software becomes available and is approved by the FAA.
Request: One commenter requested that the AD not apply to units
with software versions prior to 4.0.6, because these units broadcast a
SIL of 0 and thus are not subject to the unsafe condition.
FAA Response: We agree. We considered excluding units with software
prior to version 4.0.6 when we issued the NPRM. We did not exclude them
because our understanding of the units is that there is no
recordkeeping, marking, or indication from the unit itself that allows
an operator to identify the current software version. However, changes
to the AD in response to other comments render this exclusion
unnecessary.
Request: AOPA requested that we allow the units to remain in
service if NavWorx upgrades the internal position source with a
position source that meets the requirements of Appendix B to AC 20-
165B. Similarly, several commenters requested that we allow NavWorx to
re-certify the unit.
FAA Response: We agree. Should NavWorx upgrade its internal
position source with a position source that meets the performance
requirements of Appendix B to AC 20-165B, or demonstrate that the
internal SiRF IV GPS meets those requirements, under the provisions of
paragraph (f) of this AD, we will consider requests for approval of an
AMOC.
Request: Several commenters requested that we allow more time for
compliance. Two of those commenters requested that we delay compliance
until 2020, when the ADS-B operational rules become effective.
FAA Response: We agree with extending the compliance time. We
determined that safety will be maintained if the corrective actions are
implemented within six months of the effective date of the AD, and we
revised the AD accordingly.
We disagree with delaying compliance until 2020. The FAA's ADS-B
ground station network is already operational and in use by ATC
nationwide, and ADS-B In is also widely used in general aviation
aircraft for traffic awareness. Therefore, the fact that ADS-B Out will
not be required equipment until 2020 does not negate the unsafe
condition that exists from those units currently operating in the NAS.
Request: Many commenters requested that the FAA withdraw the NPRM
and instead work with NavWorx to address the unsafe condition. Some
commenters inferred a failure by the FAA in this regard because it
appeared it took the FAA six months to respond to NavWorx's design
change notification. A few commenters expressed disappointment and
outrage at the FAA's handling of the certification process with NavWorx
and requested we constructively and immediately resolve this situation.
FAA Response: We agree it is desirable to work with manufacturers
to resolve differences of opinion regarding product compliance and
correct identified safety concerns. The FAA made numerous efforts, in a
variety of forms and over a considerable period of time, to resolve
this situation with NavWorx. Those efforts were unsuccessful.
After receiving NavWorx's design change, the FAA advised NavWorx
that it could not manufacture the units as TSO C-154c units because
NavWorx had not provided acceptable data to substantiate modifying the
SIL value of the internal SiRF IV GPS to 3. Initially, NavWorx agreed
to return the SIL to 0 and requested 60 days to effect this change.
Instead, over two months later, NavWorx informed the FAA that it would
not be returning the SIL value to 0 after all. The FAA continued to
advise NavWorx, both verbally and in writing, that the SIL change
rendered the units non-compliant with the TSO. The FAA also continued
to request that NavWorx voluntarily return the SIL to 0, but NavWorx
refused. The FAA met with NavWorx and explained the means of compliance
in our existing guidance for certifying the SiRF IV GPS to broadcast a
SIL of 3, as well as the process for submitting an alternate or
equivalent means of compliance for approval. While NavWorx indicated
its desire to initiate one of those processes, it did not. Instead,
NavWorx continued to sell and ship the part-numbered 200-0012 and 200-
0013 units with the unapproved design change, and continued to furnish
product software upgrades through its Web site to existing owners that
contained the unapproved design change. When the FAA repeatedly
requested to conduct a routine inspection of NavWorx's facility, in
part to review NavWorx's units and data supporting its design change,
NavWorx refused.
After determining the situation created by NavWorx resulted in an
unsafe condition, and without NavWorx's cooperation to correct the
unsafe condition, the FAA found it necessary to issue an AD.
Documentation of these events is available for review in Docket No.
FAA-2016-9226.
Request: One commenter requested the FAA allow a temporary,
alternative solution in which operators would periodically validate the
units by flight test.
FAA Response: We disagree. Validation flight tests are not
engineering tests and are not designed to evaluate the unit's position
source integrity. The commenter's requested method of compliance would
not correct the unsafe condition.
Request: One commenter requested we exclude ADS-B units that are
already installed from the requirements of the AD.
FAA Response: We disagree. The FAA has determined an unsafe
condition exists on the affected ADS-B units and that removal or
correction of the units is required.
Request: Two commenters request the AD not apply to aircraft
operating under visual flight rules (VFR).
FAA Response: We disagree. The FAA has determined that an unsafe
condition with the NavWorx units exists and requires corrective action
because of the hazard they pose to other users of the NAS. The NavWorx
unit broadcasting a SIL of 3, when it is only authorized to broadcast a
SIL of 0, has the potential to incorrectly report its own position to
other aircraft and to ATC by 0.2 NM or more, without providing an
alert. Even in visual meteorological conditions, this could result in
the pilot of another aircraft visually searching the wrong sector of
sky for the incorrectly reporting ADS600-B-equipped aircraft or
incorrectly assessing the ADS600-B-equipped aircraft as not being a
collision threat, based on the depicted relative position of the
ADS600-B aircraft on its ADS-B In traffic display.
Request: EAA and two individual commenters requested the AD not
apply to experimental or light sport aircraft, since they are not
regulated in the same manner as type-certificated aircraft. EAA states
the FAA should address any valid airworthiness concerns with parts
intended for experimental aircraft through a Special Airworthiness
Information Bulletin (SAIB) or safety alert for operators (SAFO). Two
commenters requested the AD apply to experimental aircraft, because
those aircraft operate in the same airspace as type-certificated
aircraft and should use equipment with the same integrity. A few
commenters, including AOPA, requested we clarify whether the AD applies
to experimental aircraft.
FAA Response: We agree to clarify this issue. We confirm that the
AD applies to all aircraft, including experimental, and we revised the
AD to clarify the applicability. We made this AD applicable to the
ADS600-EXP P/N 200-8013 units because the design
of the Model ADS600-EXP P/N 200-8013 is substantially identical to the
Model ADS600-B P/N 200-0012 and 200-0013, specifically with regard to
the internal GPS and the SIL setting. While some commenters are correct
that the FAA has chosen to minimize regulations on experimental
aircraft because of the level of the safety risk, these risks normally
apply to the individual airplane and do not affect the overall NAS. The
safety risks defined in this AD extend beyond one aircraft and could
affect many other aircraft as well as ATC. Therefore, we find it
necessary to include experimental aircraft in the AD's applicability.
We do not agree that an SAIB or SAFO would be an appropriate
solution. These documents contain information and recommended actions
that are voluntary and not regulatory. Moreover, an SAIB is issued only
for airworthiness concerns that do not rise to the level of an unsafe
condition.
The mission of the FAA is aviation safety. ADs are used by the FAA
to correct known safety defects. It would be contrary to the intent of
the FAA's mission and statutory authority to exclude certain aircraft
when we have determined that a part installed on those aircraft has a
safety problem.

D. Comments Regarding Costs of Compliance With This AD

Request: Many commenters stated that the cost to comply with this
AD is underestimated or inaccurate and requested the FAA revise its
cost estimate. These commenters stated the cost should include the cost
to replace the unit with a new ADS-B unit and costs associated with
loss of utility; should increase the number of labor hours to account
for indirect costs such as removal and reinstallation of associated
equipment, research, and paperwork; and should increase the labor rate.
FAA Response: We disagree. The cost analysis in AD rulemaking
actions typically includes only the costs associated with complying
with the AD. In this AD, the only required action is the removal of the
unit, the deactivation of the unit, the coupling of the unit with an
approved external GPS source, or the upgrading of the software in the
unit to broadcast a SIL of 0. These actions are estimated to take 1
work-hour each, except for coupling the unit with an approved external
GPS source, which is estimated to take about 4 work-hours. The costs of
associated required actions such as installing a placard or revising
the flight manual are nominal. ADS-B Out equipment is not required for
operation until January 1, 2020, and is only required for operation in
certain specified airspace after that date. Individual operators are in
the best position to determine whether they will need to install this
equipment for the airspace they intend to operate in. Therefore,
replacement of the unit is not necessary to comply with this AD.
The labor rate of $85 per hour is provided by the FAA Office of
Aviation Policy and Plans for the FAA to use when estimating the labor
costs of complying with AD requirements.
Request: Several commenters requested the FAA revise its
determination that the AD is not a significant regulatory action. One
commenter requested the FAA analyze the costs of the AD under the
Regulatory Flexibility Act.
FAA Response: We disagree. An AD is economically significant when
the cost may have an annual effect on the economy of $100 million or
more.\7\ Even if we were to include labor for indirect costs and the
cost of replacing the unit with a new unit in our estimate, at an
estimated cost of $10,000 per aircraft and $8 million for the U.S.
fleet over the next three years, the AD would not rise to level of
economically significant. In addition, ADs correct identified unsafe
conditions, rather than raise an already adequate level of safety, and
cannot be assessed in terms of benefits balancing costs, as would be
the case for rulemaking that amends airworthiness standards.
---------------------------------------------------------------------------

\7\ A ``significant regulatory action'' is defined in Executive
Order 12866 (58 FR 51735, October 4, 1993).
---------------------------------------------------------------------------

The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA)
establishes as a principle of regulatory issuance that agencies shall
endeavor, consistent with the objective of the rule and of applicable
statutes, to fit regulatory and informational requirements to the scale
of the businesses, organizations, and governmental jurisdictions
subject to regulation. To achieve that principle, the RFA requires
agencies to solicit and consider flexible regulatory proposals and to
explain the rationale for their actions. The RFA covers a wide-range of
small entities, including small businesses, not-for-profit
organizations, and small governmental jurisdictions.
Agencies must perform a review to determine whether a proposed or
final rule will have a significant economic impact on a substantial
number of small entities. If the agency determines that it will, the
agency must prepare a regulatory flexibility analysis as described in
the RFA.
However, if an agency determines that a proposed or final rule is
not expected to have a significant economic impact on a substantial
number of small entities, section 605(b) of the RFA provides that the
head of the agency may so certify and a regulatory flexibility analysis
is not required. The FAA did make such a determination for this AD. The
basis for this determination is now discussed.
The FAA uses the Small Business Association (SBA) criteria for
determining whether an affected entity is small. For aircraft
manufacturers, aviation operators, and any business using an aircraft,
the SBA criterion is 1,500 or fewer employees.
NavWorx is a small entity, and this AD could have an adverse impact
on its business interests. Besides NavWorx, the largest number of
affected small entities would most likely be operators of ADS600-B-
equipped aircraft. Based on the estimated number of units in service,
and assuming each unit is owned by a different small entity, the
largest number of small entities affected is 800.
The FAA estimates that there is a total population of 210,000
general aviation and air taxi aircraft in the United States.\8\ Of
these, approximately 70,300 (33.5%) are flown primarily for some type
of business or commercial use and thus are potentially operated by a
small entity. Aircraft flown primarily for personal use would not be
operated by a small entity as defined by the SBA.
---------------------------------------------------------------------------

\8\ Based on the FAA General Aviation and Air Taxi Activity
Survey for calendar year 2015 (the most recent year of data
available), table 1.2, General Aviation and Air Taxi Number of
Active Aircraft by Primary Use. http://www.faa.gov/data_research/aviation_
data_statistics/general_aviation/ CY2015/media/2015_GA_Survey_Chapter_1_
Tables_16SEP2016V2.xlsx.
---------------------------------------------------------------------------

The FAA assumed all 70,300 commercial use aircraft are operated by
small entities and that each small entity operates an average of 6
aircraft,\9\ which yields an estimated number of 11,700 small entities.
We also assumed that of the 800 affected units, 33.5% (270) are used in
commercial operations.\10\ This equates to a maximum of 2.3% (270/11,700) of
small entities affected by this rule. This is not a substantial number of small
entities under the RFA.
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\9\ We based this assumption on the sanction guidance in
Appendix B of FAA Order 2150.3B, FAA Compliance and Enforcement
Program, which classifies air carriers and operators by operating
revenue, pilots employed, and aircraft operated for purposes of
determining civil penalty amounts. http://rgl.faa.gov/Regulatory_and_Guidance_
Library/. \10\ This assumption in particular is grossly high. First, some
of the affected units are installed on experimental aircraft, which
are prohibited from commercial operations and therefore could not be
used by a small entity under the RFA. Second, of the approximately
200 comments we received on the NPRM, only six commenters (NavWorx,
a charitable aircraft operator, and four avionics installation
businesses) could be presumed to be commercial entities. The
remaining comments were submitted by individuals.
---------------------------------------------------------------------------

Request: A few commenters requested or implied the FAA fund the
costs of the AD.
FAA Response: We disagree. The FAA, as a federal agency, is
responsible for all directives, policies, and mandates issued under its
authority. Although we have determined that an unsafe condition exists
with the design change to the ADS-B unit, the manufacturer is
responsible for the design change. Additionally, the FAA's budget does
not include allocations to cover AD costs incurred in modifying
privately-owned equipment.

E. Comments to the FAA's Rulemaking Process

Request: Several commenters questioned the FAA's motive in
proposing the AD. Some believed that the FAA is colluding with other
ADS-B manufacturers or industry organizations. Others suggested the FAA
is unfairly targeting NavWorx and would not be taking this action if it
involved a larger manufacturer. We interpret these comments as
requesting we withdraw the NPRM.
FAA Response: We disagree. The FAA has not communicated with any
other ADS-B product manufacturer or industry organization regarding the
compliance or safety of NavWorx products. In issuing this AD, we
followed established policy and procedures, including the public notice
and comment procedures of the Administrative Procedures Act, as well as
the DOT's ex parte policy, which can be found in Appendix 1 to 14 CFR
part 11. We placed all ex parte comments in the rulemaking docket and
considered all comments we received.
We also disagree that we are unfairly targeting NavWorx. We have
determined an unsafe condition exists on a NavWorx product and we are
requiring corrective action accordingly. If the FAA identifies similar
problems and determines that an unsafe condition exists on other ADS-B
products, whether manufactured by NavWorx or other companies, we would
take appropriate action to correct the unsafe condition.
Request: An individual commenter questioned whether we intended to
issue an AD against ADS-B transponders manufactured by Trig or Dynon.
According to the commenter, the Trig transponder allows the installer
to manually set the SIL value, and the commenter claims installers will
improperly set the SIL at 3 to obtain traffic information. The
commenter also states the Dynon ADS-B uses the same GPS source that is
the subject of this AD.
FAA Response: We are issuing this AD to correct an unsafe condition
that we have determined exists on a NavWorx product. This AD is not
applicable to Trig Avionics (Trig) or Dynon Avionics (Dynon) ADS-B
units. In the case of the older Trig units, installers are responsible
for setting the SIL appropriately based on the qualification of the
position source used. Additionally, neither the Trig units nor the
Dynon units use the SiRF IV position source.
Request: Several commenters noted they purchased a NavWorx unit
because the FAA originally listed them as eligible for the ADS-B Rebate
Program. We interpret these comments as requesting we withdraw the
NPRM.
FAA Response: We have considered the comment. When the FAA rebate
program Web site activated, it listed the ADS600-B as an eligible unit
without distinction by part number. This was consistent with NavWorx's
Web site, www.navworx.com, which advertised the ADS600-B for sale
without distinguishing between the four different unique transceiver
part numbers comprising that model series. P/N 200-0112 and P/N 200-
0113 are 2020 compliant, as these units contain a TSO-C145c approved
Accord NexNav Mini internal GPS. P/N 200-0012 and P/N 200-0013, which
are the subject of this AD, are not 2020 compliant because these units
contain the uncertified SiRF IV GPS. Once the FAA rebate program office
realized that the P/N 200-0012 and 200-0013 units were not eligible for
the rebate, it changed the Web site to identify the ADS600-B model by
P/N and listed only the P/N 200-0112 and P/N 200-0113 units as ADS600-B
equipment selection options. While the FAA regrets any inconvenience
these actions caused, what occurred with the rebate program Web site is
not relevant to whether this AD is necessary to resolve the unsafe
condition presented by the NavWorx units that improperly transmit a SIL
of 3. We did not change the AD based on these comments.
Request: One commenter states the proposed AD is contrary to the
FAA's Compliance Philosophy because we did not cooperate with NavWorx
or provide NavWorx a reasonable time to work on a corrective action.
The commenter requests we withdraw the NPRM, unless we can collect
technical data confirming a safety issue, in which case the commenter
requests any AD be issued in a non-punitive manner.
FAA Response: We disagree. The FAA's Compliance Philosophy applies
to enforcement actions taken for regulatory violations. It does not
apply to ADs, which are rulemaking actions taken to correct unsafe
conditions found in aeronautical products. Notwithstanding, we also
disagree with contentions that we failed to cooperate with NavWorx or
provide NavWorx with a reasonable amount of time to correct the unsafe
condition. The FAA clearly and repeatedly explained to NavWorx the
safety concerns with its ADS-B units and requested that NavWorx
voluntarily make the units TSO-compliant. NavWorx's failure to do so
created an unsafe condition, for which AD action is necessary.
Comment: An individual commenter stated that owners of experimental
aircraft could simply remark the affected part with a new part number
so that the AD wouldn't apply. The commenter reasoned that since the
builder of an experimental aircraft is also the manufacturer, he could
alter the part to a new design and mark it with a new part number.
FAA Response: If the FAA identifies similar problems and determines
that an unsafe condition exists on other part-numbered ADS-B products,
we would take appropriate action to correct that unsafe condition.
Also, simply changing the part number of the unit, without performing
any other corrective action, will not correct the unsafe condition that
we have determined exists in the unit. Since the unsafe condition
remains in the unit, operating an aircraft with such a unit (that has
only had the part number modified with no other corrective action
taken) would therefore be a violation of 14 CFR 91.7(a), which states
that no person may operate a civil aircraft unless it is in an
airworthy condition. Any individual taking such action is subject to a
civil penalty for a violation of the Federal Aviation Regulations.

F. Comments on the Negative Impact of the FAA's Actions

Request: Several commenters stated that the AD would create
confusion or skepticism in the flying community, and will prevent
aircraft owners from adopting new technologies promoted by the FAA in
the future. Some commenters stated that because of the AD people will
quit flying; many others stated aircraft owners will choose to operate
without ADS-B equipment. These commenters requested or implied that we
withdraw the NPRM.

FAA Response: We disagree. Although the FAA sympathizes with owners
who became early adopters of this technology in good faith and
unfortunately are now adversely affected by a situation not of their
making, the potential for this action to create skepticism and distrust
of the FAA among aircraft owners does not negate the need to correct
the identified unsafe condition. The FAA's failure to take action to
correct this unsafe condition could lead to accidents, which would also
reasonably result in skepticism and distrust of the FAA, not only on
the part of the flying community but of the public at large. We did not
change the AD based on these comments.
Request: A few commenters stated the FAA created this problem by
suddenly and unilaterally changing the operational ADS-B rules to deny
TIS-B data to aircraft broadcasting a SIL of 0. Two of these commenters
noted that NavWorx initially submitted data to substantiate a SIL of 3,
but the FAA refused to grant NavWorx TSO authorization unless the units
broadcast a SIL of 0. The commenters request the FAA provide TIS-B data
to all aircraft, regardless of SIL.
FAA Response: We disagree. The FAA's changes to only provide TIS-B
services to aircraft broadcasting a SIL greater than 0 were neither
sudden nor unilateral. The changes were announced on March 31, 2015,
and became effective in early 2016.\11\ However, they were initiated
several years prior, as the result of an FAA study to determine a low
risk, cost-effective, technically beneficial strategy for modification
of the FAA TIS-B service. During this study, we consulted with the
current manufacturers of ADS-B systems (both certified and uncertified)
designed to use TIS-B information, including Accord Technologies,
Dynon, FreeFlight Systems, Garmin, Honeywell, NavWorx, Rockwell
Collins, and Trig. Like other manufacturers, NavWorx had the
opportunity to make and obtain approval for appropriate design changes
to its equipment so its customers could receive TIS-B traffic after the
service change. NavWorx chose instead to only change the SIL setting
from 0 to 3 in software without demonstrating the existing GPS position
source's qualification to broadcast of a SIL of 3. Since that time, the
FAA has been requesting NavWorx submit testing data supporting its
conclusion that the SiRF IV GPS meets the performance requirements to
broadcast a SIL of 3. NavWorx has not provided the FAA with this data.
---------------------------------------------------------------------------

\11\ A copy of the FAA's announcement of its decision to make
changes to the TIS-B service is available for review in Docket No.
FAA-2016-9226.
---------------------------------------------------------------------------

We also disagree with the contention that NavWorx initially
submitted data to substantiate a SIL of 3. NavWorx's TSO-authorized
design for its P/N 200-0012 and P/N 200-0013 ADS-B units has always
identified the internal GPS source for those units as an uncertified
SiRF IV GPS. The SiRF IV is not manufactured under an FAA TSO. The FAA
approved this equipment and its installation to transmit a SIL of 0
because that is what is required by RTCA Document DO-282B (the
performance standard for TSO-C154c and the NavWorx units) and AC 20-
165B.
The commenters' request to provide TIS-B data to all aircraft,
regardless of SIL, would not correct the unsafe condition. We did not
change the AD based on these comments.

G. Comments Beyond the Scope of the NPRM

Request: A few commenters expressed disagreements with the ADS-B
mandate. One commenter stated compliance with the rule would put him
out of business, because he did not fly often enough to justify the
cost. Another commenter requested the mandate not apply to aircraft
operating under VFR in certain airspace. The third commenter stated
that because of the mandate, the FAA is unable to manage the increase
in ADS-B technology development or deal with the market.
FAA Response: Comments about the 2020 mandate are beyond the scope
of this AD. The rules mandating ADS-B Out usage, 14 CFR 91.225 and
91.227, were promulgated through notice and comment rulemaking that
began with an aviation rulemaking committee. An NPRM was issued in 2007
(72 FR 56947, October 5, 2007) and the comment period was subsequently
re-opened for an additional 30 days in 2008 (73 FR 57270, October 2,
2008). The final rule published on May 28, 2010 (75 FR 30160) and
considered approximately 240 comments from air carriers, manufacturers,
associations, and individuals. All documentation of this rulemaking is
available for review in Docket No. FAA-2007-29305.
Request: Some commenters requested or implied they should be given
until 2025 to comply with the AD because compliance with the ADS-B
mandate is not required for air carriers until 2025.
FAA Response: Comments about the 2020 mandate are beyond the scope
of this AD. It appears the commenters are referring to Exemption No.
12555, which is not a blanket 5-year extension for all air carriers.
Exemption No. 12555 applies only to those operators who submit a
request to use it and who comply with its conditions and limitations.
Exemption No. 12555 allows the use of current ADS-B Out systems that
are not fully compliant with the rule until fully compliant systems are
installed on or before January 1, 2025. Documentation concerning
Exemption No. 12555 is available for review in Docket No. FAA-2015-
0971.
Comment: One commenter described a safety of flight issue he
encountered with a Garmin ADS-B transponder that he has previously
reported to the FAA.
FAA Response: The comment is not relevant to whether this AD is
necessary to correct the unsafe condition presented by the NavWorx ADS-
B units broadcasting a SIL of 0. We did not change the AD based on this
comment.
Comment: A few commenters expressed criticism of the FAA in
general, without requesting specific changes to this AD.
FAA Response: The comments are not relevant to whether this AD is
necessary to correct the unsafe condition presented by the NavWorx ADS-
B units broadcasting a SIL of 0. We did not change the AD based on
these comments.

FAA's Determination

We have reviewed the relevant information, considered the comments
received, and determined that an unsafe condition exists and is likely
to exist or develop on other products of this same type design and that
air safety and the public interest require adopting the AD requirements
as proposed with the changes described previously. These changes are
consistent with the intent of the proposals in the NPRM (81 FR 72552,
October 20, 2016) and will not increase the economic burden on any
operator nor increase the scope of the AD.

Related Service Information

We reviewed NavWorx AFMS for ADS600-B as installed under STC No.
SA11172SC, approved May 4, 2014; NavWorx Installation Manual for
ADS600-B Part 23 AML STC 240-0021-00-07, Revision 7, dated May 4, 2014;
and NavWorx STC Master Drawing List 240-0013-00, Revision 10, dated May
29, 2014. This service information identifies the internal GPS position
source for the NavWorx Model ADS600-B P/N 200-0012 and P/N 200-0013 as
uncertified and not compliant with 14 CFR 91.225 and 91.227.

Costs of Compliance

We estimate that this AD affects approximately 800 ADS-B units
installed on various aircraft of U.S. registry. Operators may incur the
following costs in order to comply with this AD based on an average
labor rate of $85 per work-hour. Removing the ADS-B unit, disabling the
ADS-B unit, or revising the software of the ADS-B unit will take about
1 work-hour, for a total of $85 per aircraft. Coupling the ADS-B unit
with an approved external GPS will take about 4 work-hours for a total
of $340 per aircraft.

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.
We are 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) Is not a ``significant rule'' under DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979);
(3) Will not affect intrastate aviation in Alaska to the extent
that it justifies making a regulatory distinction; and
(4) 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.
We prepared an economic evaluation of the estimated costs to comply
with this AD and placed it in the AD docket.

List of Subjects in 14 CFR Part 39

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

Adoption of 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 (AD):