The European Aviation Safety Agency (EASA) has issued an emergency Airworthiness Directive (AD) requiring operators of EU-registered Cessna CitationJet/CJ1/CJ1+, CJ2, and CJ3 light jets fitted with Tamarack Aerospace active load-alleviation system (ATLAS) winglets to immediately deactivate those devices before continued flight. However, a Tamarack representative told AIN previously released modifications should address the agency’s concerns.
"Recently, occurrences have been reported in which Atlas appears to have malfunctioned, causing upset events where, in some cases, the pilots had difficulty to recover the aeroplane to safe flight," reads the EASA emergency AD published April 19.
Marketed as offering improved range, speed and fuel efficiency for light jets without the added weight of traditional winglet installations, Atlas uses active load-alleviation tabs–called Tamarack Active Camber Surfaces (TACS) by the company–rather than structural reinforcement to counter increased aerodynamic loading on the winglets in turns and turbulence. TACS is located outboard of each aileron and moves independently of the primary control surfaces.
Although the TACS is movement-restricted to minimize the possibility of control authority interference, the NASA Aviation Safety Reporting System (ASRS) database shows U.S. pilots have reported at least two instances of such difficulties on Atlas-equipped aircraft. One of those reports, dated February 2018, cited a "rapid onset of aileron divergent flutter on the left aileron,” requiring the pilot to reduce airspeed to alleviate the flutter condition.
(Editor's note: Following publication, Tamarack chief engineer Jacob Klinginsmith noted the referenced NASA report further states that "maintenance found the aileron trim actuator was out of tolerance. Once the actuator was replaced, the problem has not returned." The trim actuator, Tamarack pointed out, is a Cessna component.)
Service Bulletin, STC Remedy TACS Divergences
Tamarack v-p of marketing Paul Hathaway said the EASA AD appears to have been prompted by a CJ1+ operator who reported a similar “upset condition” while flying over southern England earlier this month. However, he noted the company had released a Service Bulletin in early 2018 calling for the installation of an updated TACS control unit (TCU) to resolve such issues.
"We found that a screw within the original vendor-supplied TCU could work free of its fastening structure, in some cases [causing TACS movement by] bridging a circuit,” he explained. “We’ve dispatched a field service engineer to examine the aircraft that prompted the EASA action, and to my knowledge [that aircraft] had not had the TCU Service Bulletin performed."
Earlier this year, Tamarack also released an STC upgrade kit for installation of aerodynamic centering strips on the TACS tabs. “The centering strip forces the TACS back in-trail if a fault causes the control surface to drift to an asymmetric position,” Hathaway explained.
Parts for the centering strip kit are available at no cost to current Tamarack customers, and the kit can be installed in the field, at approved service centers, or at Tamarack's facilities in Sandpoint, Idaho. “We are relatively confident we've already addressed EASA’s concerns with these modifications,” Hathaway concluded.
Until the regulators agree, operators of Atlas-equipped CitationJets/CJs must immobilize the surfaces in compliance with a Service Bulletin published by UK-based Cranfield Aerospace Solutions, pending the appropriate modifications to allow reactivation of the load-alleviation system. Aircraft flying with Atlas disabled must also comply with restrictions to indicated airspeed and maximum operating altitude to ensure the added winglet structure is not overstressed in flight.