Airworthiness Directives; THOMMEN AIRCRAFT EQUIPMENT AG Digital Air Data Computers

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.