Story ID: 
FAA Adopts AD on Tamarack Winglet Components
By: Gordon Gilbert
Caption: Directive mandates compliance with an April 2023 service bulletin
Word Count: 488
The FAA this week adopted a previously proposed airworthiness directive (AD) ordering the installation of placards and airplane flight manual changes for Cessna Citation CJ family jets equipped with Tamarack Aerospace active technology load alleviation system (Atlas) winglets. This directive was prompted by a report of the potential for a failure of certain system components in which a loss of load alleviation would be unannunciated.
Tamarack’s Atlas modifies CitationJet/CJ1, CJ2, and CJ3-series models with winglets and the Tamarack active camber surfaces (TACS), which actuate during flight to reduce the increased load on the wings caused by the winglets. Approximately 200 aircraft—about 10% of the eligible CitationJet/CJ fleet—have Tamarack winglets installed, according to the company.
Within 60 hours of time in service, or six months from Oct. 22, 2024, placards must be installed by an A&P mechanic or repair station on the left-hand inboard edge of the TACS to enhance visibility of their movement during night operations or to provide contrast if the TACS are painted a dark color. It also requires revising the AFM to include instructions for preflight checks of Atlas before taxi.
The AD essentially mandates compliance with a Tamarack service bulletin issued on April 19, 2023. Modification costs are being covered by Tamarack, which said it is also working on a permanent fix.
The AD was proposed after the company voluntarily notified the FAA that during a periodic design review, it found an Atlas failure mode that would not be annunciated to the pilot. If one of a pair of opto-isolators in the Atlas control unit fails, this would prevent an enable signal from being sent to the TACS control unit, thus preventing the TACS from operating and not providing load alleviation for the winglets. Pilots must know if the TACS aren’t working because they would need to reduce speed to prevent overloading of the wings and potentially exceeding the limit load.
In response to the proposed AD, Tamarack requested that the FAA revise the “FAA’s Determination” section, 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. The company said 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.
However, the FAA disagreed. The agency said the “FAA’s Determination” section of the proposal correlates to its finding under FAR 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.”