Airworthiness Directives; Textron Aviation Inc. (Type Certificate Previously Held by Cessna Aircraft Company) Airplanes

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 Textron (type certificate previously held by Cessna Aircraft Company) Model 525, 525A, and 525B airplanes with Tamarack ATLAS winglets installed per STC No. SA03842NY. The NPRM published in the Federal Register on March 22, 2024 (89 FR 20354). The NPRM was prompted by a report that while accomplishing a reliability improvement program, Tamarack discovered the potential for a failure of the ATLAS system in which a loss of load alleviation would be un-annunciated. The manufacturer's investigation revealed that failure of either of one of a pair of opto-isolators within the ATLAS Control Unit (ACU) can prevent an enable signal from being sent to the TACS Control Units (TCUs).

The ATLAS system is installed on Textron Model 525, 525A, and 525B airplanes under STC No. SA03842NY and lessens the increased wing loads associated with the installation of winglets. The ATLAS is designed to detect flight conditions and modify airflow at the wing tip accordingly. The ATLAS will draw power constantly to operate the logic circuit and provide power to the actuators to maintain TACS position.

The TCUs include the linear electric actuators and motor controllers that move the TACS. Since the enable signals are not monitored after the opto-isolators, the ACU cannot detect whether the generated signal is reaching the TCUs. The TCUs rely on the enable signal to determine whether to respond to commands from the ACU. If one of the opto-isolators fails, the ACU would not be able to detect that the TCUs were not enabled and the TCUs would not respond to commands from the ACU. Thus, the system would be operating in a mode of un-annunciated loss of load alleviation. The flight crew would be unaware of a malfunction of the load alleviation function of ATLAS and could fly the airplane into conditions that exceed the limit load. In addition, fatigue concerns could result in cracking of the airplane's primary structure. If not addressed, this condition could result in loss of continued safe flight and landing of the airplane.

In the NPRM, the FAA proposed to require installing placards on the left-hand inboard edge of the TACS to enhance visibility of TACS movement during night operations and revising the existing AFM for your airplane to include instructions for pre-flight checks of the ATLAS system before taxi. The FAA is issuing this AD to address the unsafe condition on these products.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from three commenters. Two of the commenters were individuals who supported the NPRM. The third commenter was Tamarack. The following presents the comments received on the NPRM from Tamarack and the FAA's response to each comment.

Request To Clarify What Prompted the NPRM

Tamarack requested that the FAA correct the SUMMARY and paragraph (e), “Unsafe Condition,” which state that the NPRM was prompted by a report of an un-annunciated failure of the ATLAS system. Tamarack commented that this statement is not accurate because even though Tamarack reported the design deficiency to the FAA under 14 CFR 21.3, “Reporting of failures, malfunctions, and defects,” there had not been any actual failures of the ATLAS system in the fleet. Tamarack stated that the “Background” section of the NPRM more accurately explains that, while accomplishing a reliability improvement program, Tamarack discovered the potential for a failure of the ATLAS system in which a loss of load alleviation would be un-annunciated.

The FAA agrees to correct the language identified by the commenter and has revised the SUMMARY and paragraph (e) of this AD accordingly.

Request To Revise “Proposed AD Requirements in This NPRM” Section

Tamarack requested that the FAA revise the “Proposed AD Requirements in This NPRM” section of the NPRM to specify who can accomplish the required actions. Tamarack stated that it is unclear whether a pilot can install the placards on the left-hand inboard edge of the TACS or whether the placards must be installed by a certificated airframe and powerplant (A&P) mechanic.

Paragraph (g) of this AD only allows a pilot to do the revision to the AFM required by paragraph (g)(2) of this AD and does not allow a pilot to do the installation of placards required by paragraph (g)(1) of this AD. An FAA-certificated A&P mechanic or repair station must install the placards on the left-hand inboard edge of the TACS. The FAA has not revised the “Proposed AD Requirements in This NPRM” section as requested by the commenter because that section of the NPRM is not carried over into this final rule.

Request To Revise “FAA's Determination” Section of the NPRM

Tamarack requested that the FAA revise the “FAA's Determination” section of the NPRM, which states that the FAA has determined that the unsafe condition is likely to exist or develop on other products of the same type design. Tamarack stated that the probability of the unsafe condition is “remote” and not “likely” and therefore using “likely” misrepresents the probability of the identified unsafe condition occurring in the fleet.

The FAA disagrees. The “FAA's Determination” section of the NPRM correlates to the FAA's finding under 14 CFR 39.5, which states the conditions that must be present when the FAA issues an AD. If an unsafe condition only exists on one product and is not likely to exist or develop on other products of the same type design, or if there are no other existing products of the same type design, the FAA will accomplish corrective action through means other than an AD. The FAA's finding under 14 CFR 39.5 is unrelated to the probability of the failure condition described by the commenter. The FAA did not revise this final rule regarding this issue.

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 the change described previously, this AD is adopted as proposed in the NPRM.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Tamarack Aerospace Atlas Service Bulletin SBATLAS-57-06, Issue A, dated April 19, 2023. This material specifies procedures for installing placards on the left-hand inboard edge of the TACS to enhance visibility of TACS movement during night operations.

The FAA also reviewed the following AFM supplements, which contain, among other items, instructions for pre-flight checks of the ATLAS system before taxi. These documents are distinct because they apply to different airplane models.

• Tamarack Aerospace Cessna Citation Model 525, 525-0001 thru -0359, AFM Supplement TAG-1101-0099 CA/DD/M023, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue D, dated September 20, 2023.
• Tamarack Aerospace Cessna Citation Model 525, 525-0360 through -0599, AFM Supplement TAG-1101-1099 CA/DD/M037, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue D, dated September 20, 2023.
• Tamarack Aerospace Cessna Citation Model 525, 525-0600 through -0684 and -0686 through -0701, AFM Supplement TAG-1101-P099 CA/DD/M038, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue D, dated September 20, 2023.
• Tamarack Aerospace Cessna Citation Model 525, 525-0685 and -0800 and on, AFM Supplement TAG-1101-M099 CA/DD/M088, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue D, September 20, 2023.
• Tamarack Aerospace Cessna Citation Model 525A, 525A-0001 thru -0299, AFM Supplement TAG-1102-0099 CAS/AFM0003, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue C, September 20, 2023.
• Tamarack Aerospace Cessna Citation Model 525A, 525A-0300 and on, AFM Supplement TAG-1102-P099 CAS/AFM0004, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue C, September 20, 2023.
• Tamarack Aerospace Cessna Citation Jet Model 525B, 525B-0001 thru 525B-0056 and 525B-0058 thru 525B-0450, AFM Supplement TAG-1103-0099 CAS/AFM0001, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue C, September 20, 2023.
• Tamarack Aerospace Cessna Citation Jet Model 525B, 525B-0057 and 525B-0451 and ON, AFM Supplement TAG-1103-P099 CAS/AFM0002, Tamarack Active Technology Load Alleviation System (Atlas) Winglets, Issue D, September 20, 2023.

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.

Costs of Compliance

The FAA estimates that this AD affects 148 airplanes of U.S. registry.

The FAA estimates the following costs to comply with this AD: