The FAA has grounded all Cessna Citation Model 525, 525A, and 525B (CJ1, CJ2, and CJ3) light jets equipped with Tamarack Aerospace active load alleviation (Atlas) winglets. The action follows last month’s issuance of an emergency airworthiness directive (AD) by the European Union Aviation Safety Agency (EASA), and while a reciprocal directive from U.S. regulators was expected, a Tamarack representative expressed “disappointment” to AIN at the timing and wording of the FAA action.

Similar to the EASA AD, the FAA’s May 24 directive requires Atlas to be disabled; however, the agency was not satisfied with the proposed mitigation in the EASA AD—use of “speed tape” to secure the Tamarack Active Camber Surfaces (TACS) in neutral position—and will not allow operation of the 76 Atlas-equipped CJs in the U.S. outside of approved ferry flights until a better alternative is identified.

“Use of speed tape was never a Tamarack solution, and in the course of harmonizing to the EASA directive the FAA noted its use wasn’t acceptable,” said Paul Hathaway, Tamarack’s vice-president of marketing. “However, we have over the past year issued two service bulletins at company expense to address potential TACS asymmetry, and those modifications have been submitted to both aviation authorities as an alternate means of compliance (AMOC) to resolve the directives.”

Those bulletins call for replacement of a screw inside the TACS control unit (TCU) that could work free of its fastening structure and drive TACS movement, and installation of aerodynamic centering strips to force the control surfaces back in-trail if a fault causes them to drift to an asymmetric position. Hathaway noted no further control issues have been reported on aircraft complying with either or both of the bulletins. The first bulletin for repair of the TCU is mandatory, while the centering-strip bulletin is optional (unless the FAA decides to make it mandatory as part of an AMOC). 

“We have petitioned the FAA and EASA with our own flight test data, an extensive white paper, and flight test videos demonstrating these modifications are the best corrective paths to return these aircraft to service with Atlas enabled,” he stated. 

The FAA directive noted five reported control loss incidents involving Atlas-equipped aircraft to the agency and EASA. In one of those incidents, however, Atlas appears not to have been involved. The December 2018 incident was documented in a NASA Aviation Safety Reporting System (ASRS) narrative, in which the submitter responded to a callback from NASA. In the ASRS report NASA wrote in the callback section, “On the reporter's aircraft, maintenance found the aileron trim actuator was out of tolerance. Once the actuator was replaced, the problem has not returned.”

The agency also cited an ongoing National Transportation Safety Board (NTSB) investigation into a November 2018 fatal accident in Indiana that involved an Atlas-equipped CJ2+ that had complied with the mandatory TCU service bulletin; however, Hathaway emphatically stated the NTSB has not yet contacted the company as part of that investigation. 

“We’ve offered our input and have been told it is not needed,” he continued. “I can’t definitively say the Board has ruled out Atlas [as causal to the accident] but we’ve been told by other agencies it would be highly unusual to have not been contacted if they believed the system was relevant to the investigation.” (An NTSB spokesperson told AIN last month the investigation “is still ongoing at this time. Only preliminary information is available.”) While the aircraft manufacturer Textron Aviation and engine manufacturer Williams International are party to the investigation, Tamarack Aerospace is not a party.

In the FAA’s discussion of the reasoning for the AD, it stated the following: “The NTSB investigation focuses on the role the Atlas may have played in the accident.” AIN has asked the FAA whether it was specifically told that the NTSB’s investigation is focusing on Atlas, but the agency didn’t respond by the time this was published. 

Hathaway also noted a discrepancy in the pilot’s account of the incident that drove issuance of the original EASA Emergency AD, involving a CJ1+. “The pilot claimed his aircraft rolled to 90 degrees in one second, and a CJ simply cannot roll that quickly,” he said. “Flight data recovered by the UK Air Accidents Investigation Branch (AAIB) and EASA, directly from the aircraft’s AHRS [attitude and heading reference system], shows the roll event occurred over 18 seconds.

“That matches our own flight test data for TCU failure,” Hathaway continued, “and should have been an easily-recoverable scenario, but the pilot did not follow the recovery procedure specified by Tamarack.” The aircraft did eventually return to level flight and landed safely. The UK CJ1+ also had not complied with the mandatory TCU service bulletin, according to Tamarack, and when its TCU was examined, it was found to have the loose-screw problem identified in the bulletin. 

For the moment, Hathaway stated the company eagerly awaits FAA approval of the service bulletin AMOCs to return U.S. operators to flight, a process likely to be drawn out by the Memorial Day weekend in the U.S. as well as the agency’s “post-[Boeing 737] Max” sensitivity to reports of aircraft control issues. 

“Our customers are concerned, but they realized we’ve conducted ourselves in an open, honest, and transparent manner,” he concluded. “Frankly, there’s a lot of frustration, but we’re confident we’ve brought the regulators up to speed on how our product works.”