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Tamarack petitions NTSB to reconsider crash cause

Winglet maker disputes findings in 2018 jet crash

The maker of a system of winglets and automated control surfaces cited by the NTSB as the probable cause of a fatal 2018 crash petitioned the board to reconsider its findings on January 3.

The NTSB determined that asymmetric activation of the left-side automated control surface designed to alleviate loads induced by winglets installed with Tamarack's Active Technology Load Alleviation System probably caused a fatal crash in November 2018. Tamarack disputed that conclusion. Photo by Chris Rose.

Tamarack Aerospace Group noted in its petition that the NTSB final report on the 2018 crash of a Cessna Citation in Indiana was issued four business days after the company filed its own report to the investigation. Tamarack remains a party to the investigation of this crash because the Cessna Citation was equipped with Tamarack's winglets and Active Technology Load Alleviation System (ATLAS), a malfunction of which was found by the NTSB to be the probable cause of the crash. 

Tamarack, in its petition, asserts that the investigation ignored the findings presented by Tamarack on October 26, including a different theory of the crash sequence and cause that attributes the apparently uncommanded roll to failures in the attitude and heading reference system (AHRS) and/or the autopilot, which disconnected outside of the bank angle and roll rate parameters that would trigger that event by design.

"There is nothing in the public docket or the Final Accident Report that addresses this system anomaly or any other information contained in the submission," Tamarack noted in the petition, a copy of which was provided to AOPA. "Given that the accident occurred 35 months prior to the date of publication of the Final Accident Report, it is difficult to comprehend the NTSB's apparent rush to judgment in publishing its Report a mere 4 business days after receiving valid questions and a credible theory of the accident in Tamarack's supplemental party submission."

Tamarack further requested "the opportunity to make a verbal/oral presentation to the Board and for the presentation to be recorded and made available in the public docket."

Federal regulations governing the NTSB preclude reconsideration of findings based on "positions previously advanced," though Tamarack asserted in its petition that, "Given the exceedingly short timeframe between Tamarack's submission of its supplemental party submission and the NTSB’s publication of its Final Accident Report, [49 CFR] § 845.32(b) is not applicable."

The lone pilot and two passengers of the ATLAS-equipped Citation died in the 2018 crash shortly after departure while climbing to an assigned altitude of 10,000 feet. The investigation determined that the flight, in instrument meteorological conditions, reached a maximum altitude of 6,100 feet before rolling out of control, descending into terrain at high velocity. The pilot made a mayday call reporting he was "unable to gain control of the aircraft" during the 35 seconds between the onset of the roll and impact.

NTSB investigators noted witness marks on the bellcrank of the left-side Tamarack active camber surface (TACS) that led them to conclude that automated control surface, an integral part of ATLAS, was deflected in a trailing-edge-up position on impact.

"Additional damage on the TACS inboard hinge fitting, consistent with overdeflection in the trailing-edge-up direction, was also consistent with the TACS being in a trailing-edge-up position at the time of ground impact," the NTSB report states. "Examination of the left TCU [TACS Control Unit] showed contact marks on the ram guide housing and on the extend hard stop plate, which were consistent with the actuator being at a maximum extension position at the time of ground impact. These marks are not expected during normal operation of the actuator. The evidence indicates that the left TACS was in a position consistent with full trailing edge up position at the time of ground impact."

Tamarack asserted in its petition that the NTSB reached inconsistent conclusions regarding the degree and timing of the TACS deflection, and that the witness marks cited by investigators were made during the impact, not while the aircraft was still airborne. Tamarack's position on this point is not completely inconsistent with the NTSB findings, which also attribute the witness marks in question to impact forces; the principal difference between the positions is the timing of when and how those marks were made, and whether the active control surface was deflected while the aircraft was still airborne.

Tamarack noted evidence of multiple witness marks corresponding to different control surface deflection angles, and added that given what is known about the impact sequence, "it is possible that the left-hand actuator was subjected to more than one impact…. It is also probable that the high energy contact marks on the extension hard stop within the left-hand actuator were caused during the impact, as the left-hand TACS was forced to an extreme trailing edge up deflection with sufficient force to cause multiple structural failures in multiple elements of the TACS installation."

Tamarack noted in its petition that the final NTSB report does not indicate why the Citation's autopilot disconnected at a bank angle of 30 degrees, short of the 45-degree threshold at which that system was designed to disconnect: "If the autopilot did not disconnect due to bank angle or roll rate, ATLAS could not have caused the autopilot to disconnect. Critically, the Final Report does not identify the specific probable cause why the autopilot disconnected."

The NTSB confirmed via email on January 4 that it has received the petition for reconsideration, and the board will, as the relevant regulation requires, "review the petition to determine if it introduces new evidence or if it shows that the NTSB’s findings are erroneous. If either of those two conditions is met, the petition will be considered by the Board, which will vote to accept or reject the petition, in whole or in part."

Preliminary findings from the Indiana crash investigation, along with five reports of uncommanded rolls by ATLAS-equipped Cessna Citations submitted to the European Union Aviation Safety Agency in 2018 and 2019, prompted the FAA to ground all 91 Citations then equipped with ATLAS winglets on May 24, 2019. Tamarack filed for Chapter 11 bankruptcy protection in June 2019. The FAA approved an alternative method of compliance on July 10, 2019, that allowed ATLAS-equipped aircraft to resume flying once they were in compliance with two service bulletins, only one of which had been completed on the 2018 accident aircraft; the second was issued after the crash.

Tamarack continued operation—and ATLAS installations—while working through the bankruptcy process that culminated, with all creditors paid in full, in August; Tamarack reported in September that 50 additional ATLAS installations had been completed during the bankruptcy.

Tamarack has since begun installing ATLAS retrofits on Beechcraft King Airs, fitting the fuel-saving modifications to turboprops for defense-related missions, as AOPA Editor at Large Tom Horne reported in the January issue of AOPA Pilot, Turbine Edition.

"Tamarack's concern for safe aviation and truth triggered its formal request that the NTSB reconsider its questionable determination," the company states in the petition. "Tamarack responds in its demand for a reconsideration by the NTSB that the 'undetermined reasons' cited by the NTSB’s report were indeed undetermined because objective forensic evidence cited in our supplemental party submission to the NTSB, all before the Final Report was released, was either ignored or misinterpreted."

Federal regulations require that other parties to the investigation (including, in this case, the aircraft and avionics manufacturers) be provided copies, with proof of service attached to the petition, and that any party served may file comments "no later than 90 days after service of the petition." The regulation does not impose a deadline on the NTSB, nor does it require the board to modify its findings.

Jim Moore
Jim Moore
Managing Editor-Digital Media
Digital Media Managing Editor Jim Moore joined AOPA in 2011 and is an instrument-rated private pilot, as well as a certificated remote pilot, who enjoys competition aerobatics and flying drones.
Topics: Accident, Aircraft Systems

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