The US National Transportation Safety Board (NTSB) has revised a 2021 accident report to remove a conclusion that Tamarack Aerospace’s Atlas active winglets caused a deadly Cessna Citation 525 crash in 2018.

“Available evidence for this accident does not sufficiently show that the Atlas [winglet system] was the cause of the in-flight upset from which the pilot was unable to recover,” the NTSB said in a 26 February letter to Idaho-based Tamarack.

Evidence is “insufficient to conclude” that the left winglet was extended at the time of impact or that the Atlas system caused the jet to roll left, it adds.

cesnna-winglet-c-Tamarack Aerospace

Source: Tamarack Aerospace

Idaho-based Tamarack makes winglets for Cessna 525 Citations.

The NTSB’s move came in response to a January 2021 petition filed by Tamarack, which has long insisted its winglet system did not cause the jet (registration N525EG) to crash shortly after taking off from Clark Regional airport in Jeffersonville, Indiana.

The accident killed the pilot and two passengers.

The NTSB has updated its final accident report to reflect the new conclusions. The revised report, dated 23 February, attributes the crash to “the pilot’s inability to regain airplane control after a left roll that began for reasons that could not be determined based on the available evidence”.

“It is unlikely that the pilot commanded the left bank,” the report adds.

The NTSB had previously concluded that the Citation’s Tamarack winglets deployed asymmetrically, causing the jet to roll left and descend into the ground.

“This reversal shows the NTSB has the courage, professionalism and proper process to make these corrections, and for that we applaud the NTSB,” says Tamarack president Jacob Klinginsmith.

The NTSB’s initial report contained conclusions “that could not be supported by the facts of that accident”, it adds.

Tamarack’s Atlas active winglets, available as an option on Citations, deploy automatically to alleviate loads, counter turbulence and improve efficiency.

The NTSB’s revision follows several difficult years for Tamarack. In addition to the 2018 crash, US and European regulators in 2019 grounded Atlas-equipped Citations after several instances involving in-flight uncommanded rolls due to a technical problem.

Regulators lifted the grounding within months for Citations with fixes. The Citation involved in the deadly 2018 crash had been equipped with those fixes.

The grounding pushed Tamarack in 2019 to file for US court-supervised bankruptcy protection, from which it emerged in 2021. Tamarack has meanwhile been seeking to sell its active winglets as modification for other aircraft types.

Shortly after taking off from Jeffersonville, the Citation involved in the 2018 accident began rolling left, apparently catching the pilot by surprise. It continued climbing and banking, reaching about 6,100ft before beginning a rapid descent, with its bank angle hitting 90°, the NTSB said.

The pilot issued a mayday call and said he was unable to control the jet, which then crashed about 13.7km (8.5 miles) from the airport.

The NTSB based its initial conclusion – that a winglet erroneously deployed – partly on post-crash damage to the winglet system.

It now says damage could have been caused by the crash itself.