February 29, 2024 By Niki Britton
Previously attributed to a malfunction of Tamarack’s active winglet system, the NTSB now says that the probable cause of a 2018 crash of a Cessna Citation could not be determined based on the available evidence.
Tamarack's fuel-saving winglet system, which includes automated control surfaces, is no longer deemed the probable cause of a 2018 crash. Photo by Chris Rose.
Tamarack Aerospace Group, based in Sandpoint, Idaho, created the Active Technology Load Alleviation System (ATLAS) that includes winglets to increase lift and aerodynamic efficiency, coupled with automated control surfaces similar to ailerons that are directed by a control unit to move in response to increased wing loads, and offset those loads. The system allows winglet retrofits without requiring additional structure to be added, along with weight. Those control surfaces were installed on dozens of aircraft by the time a Cessna Citation CJ2 on an IFR flight from Indiana to Chicago crashed after a loss of control in flight. The NTSB investigation determined, in 2021, that the ATLAS system had malfunctioned, inducing a roll from which the aircraft did not recover.
Tamarack hotly disputed that finding, and petitioned the NTSB to reconsider its probable cause determination in January 2022. The board's response arrived in a 12-page letter dated February 26, with the amended probable cause report attached.
In a rare (if not unprecedented) reversal the board wrote that Tamarack's petition "is granted in part because the available evidence for this accident does not sufficiently show that the ATLAS was the cause of the in-flight upset from which the pilot was unable to recover. In addition, the factual and analysis sections of the report and the findings have been revised to reflect the information presented in the petition response sections addressing witness marks, [control unit] bent pins, and the UK uncommanded roll event."
The FAA grounded all ATLAS-equipped aircraft (91 at the time) in May 2019, while the investigation of the Indiana accident was ongoing, citing that investigation along with six reports of uncommanded roll events submitted to the Aviation Safety Reporting System, or to European regulators. Tamarack filed for bankruptcy protection soon after, though the company continued to produce and install active winglets, and emerged from bankruptcy in 2021...
