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Citation CJ2 with active Tamarack wingletsOn Friday the FAA proposed a new airworthiness directive for Textron Aviation models with Tamarack Active Technology Load Alleviation System winglets installed, including the Cessna Citation Jet M2, CJ2 and CJ3. The FAA is asking for comments on the AD by May 6.
The AD was issued in response to a report of an unannunciated failure of the ATLAS system, requiring the installation of placards on the left-hand inboard edge of the Tamarack active camber surface and a revision of the existing airplane flight manual. Then initial report was received after Tamarack while undergoing a reliability improvement program, discovered the potential for a failure in the system, which is a loss of load alleviation and unannunciated. Tamarack's investigation revealed that a failure of either one of a pair of opto-isolators within the ATLAS Control Unit would prevent an enable signal from being sent to the TACS Control Units.Read the proposed AD here and submit your own comments
The ATLAS system installed on some Citation jets under STC No. SA03842NY 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 system will draw power constantly to operate the logic circuit and provide power to the actuators to maintain the TACS position.
The TCUs include linear electric actuators and motor controllers that move the TACS. Since the enable signals are not monitored after the opto-isolators, the ACU is unable to detect whether the generated signal is reaching the TCUs. These TCUs rely on an enable signal to determine whether a response is needed for commands from the CU. If one of the opto-isolators fails the ACU will be unable to detect that the TCUs were not enabled and the TCUs would not respond to commands from the ACU. In this case, the system would operate in a mode of unannunciated loss of load alleviation. The flight crew would be unaware of the malfunction of the load alleviation function of the ATLAS and could continue to fly the plane into conditions that would exceed the limit load. Fatigue concerns could also result in the cracking of the plane's primary structure. If these concerns are not addressed, the condition could result in loss of continued safe flight and landing of the airplane.
The Notice of Proposed Rulemaking was issued to determine that the unsafe condition described is likely to exist or develop on other products with the same type design. The FAA reviewed Tamarack's Service Bulletin SBATLAS-57-06, Issue A from April 19, 2023 which specified procedures for installing placards on the left-hand inboard edge of the TACS to enhance visibility of TACS movement during night operations. The FAA has also reviewed AFM supplements that contain instructions for pre-flight checks of the ATLAS system before taxi, applying to different models including the Citation CJ2, CJ2+, CJ3 and CJ3+.
With the proposed AD, 148 planes on the U.S. registry would be affected, costing about $9,250 for operators to install placards and about $12,580 to revise AFMs. The AD applies to all Cessna Model 525, 525A and 525B planes, including all serial numbers. If this AD passes, operators must comply within 60 hours of time-in-service or six months after the effective date of the AD, or whichever occurs first.RELATED STORY:NTSB no longer blames Tamarack system, rewrites 2018 Citation crash report
This follows the NTSB's reversal of its findings for a deadly Citation CJ2 crash in 2018, granting Tamarack's petition and stating that the available evidence could not sufficiently conclude that the ATLAS system caused the crash. Initially, the NTSB found that an electric failure in the system likely caused one of the control surfaces to deploy separately, causing an uncommanded roll. The pilot was not aware of any supplementary procedures and these procedures did not explain the significance of the system failure or address the failure in all flight conditions. After the 2018 crash that killed three people, the FAA grounded all Cessna planes equipped with ATLAS winglets, which was lifted in 2019. After the report was issued, Tamarack submitted a petition, asking the NTSB to reconsider the findings, citing numerous inconsistencies and evidence that could be lined with the force of impact, not position in flight. Last month, the NTSB reversed its findings and changed its findings in the report and public docket.