Airworthiness Directives; MHI RJ Aviation ULC (Type Certificate Previously Held by Bombardier Inc.) Airplanes

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-2024-1896; Project Identifier MCAI-2023-00978-T” 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 the 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 Steven Dzierzynski, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; telephone 516-228-7300; email 9-avs-nyaco-cos@faa.gov. Any commentary that the FAA receives that is not specifically designated as CBI will be placed in the public docket for this rulemaking.

Background

The FAA issued AD 2023-10-02, Amendment 39-22438 (88 FR 34065, May 26, 2023) (AD 2023-10-02) to address the effect of interference from wireless broadband operations in the 5G C-Band on all transport and commuter category airplanes equipped with a radio altimeter. AD 2023-10-02 was prompted by a determination that radio altimeters cannot be relied upon to perform their intended function if they experience interference from wireless broadband operations in the 5G C-Band. AD 2023-10-02 requires revising the limitations section of the existing airplane flight manual to incorporate limitations prohibiting transport and commuter category airplanes from performing certain low-visibility landing operations at any airport unless they have upgraded their radio altimeters. Transport Canada, which is the aviation authority for Canada, issued corresponding Transport Canada AD CF-2023-46, dated June 30, 2023, to require similar limitations on flight operations requiring radio altimeter data in U.S. airspace affected by 5G C-Band wireless signals.

Additionally, Transport Canada has issued Transport Canada AD CF-2023-62R1, dated November 21, 2023 (referred to as “the MCAI”), for certain serial-numbered MHI RJ Aviation ULC Model CL-600-2B19 (Regional Jet Series 100 and 440), CL-600-2C10 (Regional Jet Series 700, 701, and 702), CL-600-2C11 (Regional Jet Series 550), CL-600-2D15 (Regional Jet Series 705), CL-600-2D24 (Regional Jet Series 900), and CL-600-2E25 (Regional Jet Series 1000) airplanes. The MCAI states that, in addition to the effects of 5G C-Band broadband interference identified in FAA AD 2023-10-02, MHI RJ has determined that 5G C-Band broadband interference can result in certain failure messages and aural alerts being inhibited longer than intended. Specifically, this can result in the inhibition of hydraulic system #3 and wing anti-ice overheat failure messages such that flightcrew are unable to perform appropriate airplane flight manual (AFM) procedures in the time needed to prevent loss of elevator control due to hydraulic system overheat and wing structural damage due to wing anti-ice system overheat. This condition, if not corrected, could result in delayed flightcrew response leading to loss of continued safe flight and landing.

The MCAI requires the installation of a new RF bandpass filter on the coaxial line between the radio altimeter and the receive antenna in the aft equipment compartment. For airplanes with a dual radio altimeter configuration, the MCAI requires a filter to be installed on both systems or on one system provided the second system is deactivated. When the airplane is modified as specified in the MCAI, the configuration with the RF bandpass filter installed has been determined to be “radio altimeter tolerant.” The actions of the MCAI apply only to airplanes operating within the contiguous U.S. airspace.

The FAA is proposing this AD because radio altimeter anomalies can result in the inhibition of certain failure messages such that the flightcrew are unable to perform appropriate AFM procedures in the time needed to prevent loss of elevator control due to hydraulic system overheat and wing structural damage due to wing anti-ice system overheat, possibly resulting in delayed flightcrew response leading to loss of continued safe flight and landing.

You may examine the MCAI in the AD docket at regulations.gov under Docket No. FAA-2024-1896.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed MHI RJ Service Bulletins 601R-34-152, Revision D, dated May 11, 2023, and 670BA-34-054, dated February 20, 2023. This material specifies procedures for installing a new RF bandpass filter on the coaxial line between the radio altimeter and the receive antenna in the aft equipment compartment. These documents are distinct since they apply to different airplane models. 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

This product has been approved by the aviation authority of another country and is 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 material 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 accomplishing the actions specified in the material already described. This AD would not apply to airplanes that have been modified to be a radio altimeter tolerant airplane under the requirements of AD 2023-10-02.

Differences Between the MCAI and This NPRM

Although the actions of the MCAI apply only to Canadian-registered airplanes operating within the contiguous U.S. airspace, this proposed AD would apply to U.S.-registered airplanes operating in any airspace. The FAA has determined that the expansion of 5G C-band has occurred in other countries, such as Canada and Brazil, in which 5G C-band interference is expected.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect up to 873 airplanes of U.S. registry. However, many of these airplanes may already have a bandpass filter installed in compliance with AD 2023-10-02 and would not have any costs because of this proposed AD. The FAA estimates the following costs to comply with this proposed AD: