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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2024-2322; Project Identifier MCAI-2024-00065-Q]
RIN 2120-AA64
Airworthiness Directives; THOMMEN AIRCRAFT EQUIPMENT AG Digital
Air Data Computers
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain THOMMEN AIRCRAFT EQUIPMENT AG (THOMMEN) AC32 Digital Air
Data Computers. This proposed AD results from occurrences of AC32
Digital Air Data Computers (ADCs) that stop functioning below certain
temperatures. This proposed AD would require replacing an affected AC32
Digital ADC with a serviceable part. The FAA is proposing this AD to
address the unsafe condition on these products.
DATES: The FAA must receive comments on this NPRM by November 14, 2024.
ADDRESSES: You may send comments, using the procedures found in 14 CFR
11.43 and 11.45, by any of the following methods:
Federal eRulemaking Portal: Go to regulations.gov. Follow
the instructions for submitting comments.
Fax: (202) 493-2251.
Mail: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE, Washington, DC 20590.
Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2024-2322; 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 NPRM, the mandatory continuing airworthiness
information (MCAI), any comments received, and other information. The
street address for Docket Operations is listed above.
Material Incorporated by Reference:
For THOMMEN AIRCRAFT EQUIPMENT material identified in this
proposed AD, contact THOMMEN AIRCRAFT EQUIPMENT AG, Hofackerstrasse 48,
4132 Muttenz, Switzerland; phone: +41 (0) 61 965 22 22; email:
sales@thommen.aero; website: thommen.aero.
You may view this material at the FAA, Airworthiness
Products Section, Operational Safety Branch, 901 Locust, Kansas City,
MO 64106. For information on the availability of this material at the
FAA, call (817) 222-5110.
FOR FURTHER INFORMATION CONTACT: William Reisenauer, Aviation Safety
Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590;
phone: (516) 228-7301; email: 9-AVS-AIR-BACO-COS@faa.gov.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites you to send any written relevant data, views, or
arguments about this proposal. Send your comments to an address listed
under ADDRESSES. Include "Docket No. FAA-2024-2322; Project Identifier
MCAI-2024-00065-Q" at the beginning of your comments. The most helpful
comments reference a specific portion of the proposal, explain the
reason for any recommended change, and include supporting data. The FAA
will consider all comments received by the closing date and may amend
this proposal because of those comments.
Except for Confidential Business Information (CBI) as described in
the following paragraph, and other
information as described in 14 CFR 11.35, the FAA will post all
comments received, without change, to regulations.gov, including any
personal information you provide. The agency will also post a report
summarizing each substantive verbal contact received about this NPRM.
Confidential Business Information
CBI is commercial or financial information that is both customarily
and actually treated as private by its owner. Under the Freedom of
Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public
disclosure. If your comments responsive to this NPRM contain commercial
or financial information that is customarily treated as private, that
you actually treat as private, and that is relevant or responsive to
this NPRM, it is important that you clearly designate the submitted
comments as CBI. Please mark each page of your submission containing
CBI as "PROPIN." The FAA will treat such marked submissions as
confidential under the FOIA, and they will not be placed in the public
docket of this NPRM. Submissions containing CBI should be sent to
William Reisenauer, Aviation Safety Engineer, FAA, 1600 Stewart Avenue,
Suite 410, Westbury, NY 11590. Any commentary that the FAA receives
which is not specifically designated as CBI will be placed in the
public docket for this rulemaking.
Background
The European Union Aviation Safety Agency (EASA), which is the
Technical Agent for the Member States of the European Union, has issued
EASA AD 2024-0024, dated January 24, 2024 (also referred to as the
MCAI), to correct an unsafe condition on certain THOMMEN AC32 Digital
ADCs. The MCAI states that there have been occurrences of certain AC32
Digital ADCs stopping functioning at temperatures below -20 degrees
Celsius. The error is detectable and does not transmit erroneous data.
The problem is caused by the power module and the affected units have
been identified. This condition, if not addressed, could result in
insufficient navigational data provided to the flight crew, resulting
in reduced control of the aircraft. The MCAI requires removing from
service each affected part and specifies that only serviceable parts as
defined in the MCAI may be installed.
You may examine the MCAI in the AD docket at regulations.gov under
Docket No. FAA-2024-2322.
Material Incorporated by Reference Under 1 CFR Part 51
The FAA reviewed THOMMEN AIRCRAFT EQUIPMENT Service Bulletin SB
AC32/07, Revision 1.0, dated August 31, 2023 (THOMMEN SB AC32/07,
Revision 1.0). This material specifies procedures for determining if an
aircraft is equipped with an affected AC32 Digital ADC listed in
Appendix A, determining if the actions specified in THOMMEN SB AC32/07,
Revision 1.0, were already accomplished, and replacing any affected
THOMMEN AC32 Digital ADC.
This material is reasonably available because the interested
parties have access to it through their normal course of business or by
the means identified in the ADDRESSES section.
FAA's Determination
These products have been approved by the aviation authority of
another country and are approved for operation in the United States.
Pursuant to the FAA's bilateral agreement with this State of Design
Authority, it has notified the FAA of the unsafe condition described in
the MCAI referenced above. The FAA is issuing this NPRM after
determining that the unsafe condition described previously is likely to
exist or develop on other products of the same type design.
Proposed AD Requirements in This NPRM
This proposed AD would require replacing affected AC32 Digital ADCs
with serviceable parts. This proposed AD would also prohibit the
installation of an affected AC32 Digital ADC on any aircraft.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would
affect 401 AC32 Digital ADCs that are installed on aircraft worldwide.
The FAA has no way of determining how many of these ADC are installed
on aircraft of U.S. registry.
The FAA estimates the following costs to comply with this proposed
AD. These costs assume all 401 AC32 Digital ADCs are installed on
aircraft of U.S. registry. The FAA expects a portion of the affected
population to exist outside of the U.S. and the estimated costs to be lower.
Estimated Costs
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ACTION
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LABOR COST
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PARTS COST
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COST PER PRODUCT
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COST ON U.S. OPERATORS
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Replace affected AC32 Digital ADC
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12 work-hours x $85 per hour = $1,020.
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$4,477
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$5,497
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$2,204,297
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The FAA has included all known costs in its cost estimate.
According to the manufacturer, however, some of the costs of this
proposed AD may be covered under warranty, thereby reducing the cost
impact on affected operators.
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
The FAA determined that this proposed AD would not have federalism
implications under Executive Order 13132. This proposed AD would 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 this proposed regulation:
(1) Is not a "significant regulatory action" under Executive
Order 12866,
(2) Would not affect intrastate aviation in Alaska, and
(3) Would 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 Proposed Amendment
Accordingly, under the authority delegated to me by the
Administrator, the FAA proposes to amend 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:
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