Tamarack active winglets prompt AD

The European Union Aviation Safety Agency (EASA) emergency airworthiness directive cited flight crew reports that the active load alleviation system (ATLAS) installed with Tamarack winglets malfunctioned, causing “upset events where, in some cases, the pilots had difficulty to recover the aeroplane to safe flight.”

The active winglets each pair a simple vertical winglet with an adjacent horizontal control surface that acts as a miniature, automated aileron. The computer-driven control surface moves without requiring pilot input to adjust aerodynamic loading. While actuation without pilot participation is part of the design, in a handful of cases it caused problems including aircraft upset and aileron flutter, which forced another pilot to slow the Cessna down. The system made by Tamarack Aerospace Group of Sandpoint, Idaho, has been installed on more than 90 aircraft to date under supplemental type certificates applicable to a range of Cessna Citation models, according to Tamarack Vice President of Marketing Paul Hathaway.

The retrofit required a retrofit, and the company issued a service bulletin about a year ago to correct a problematic fastener. A loose screw contacting the circuit board during flight prompted an abnormal deployment of the control surface. Hathaway said all of the affected aircraft are among “a handful” still awaiting modifications to the control surface itself, as well as the control unit that commands it. The changes were approved by the FAA and EASA via supplemental type certificate in March. That STC and the preceding service bulletin from the company stipulate installation of a “centering strip” to prevent the control surface from extending if the system is powered off, and a change to the control unit to better protect the circuit board in the unlikely event that another loose screw should ever “migrate” in flight.

Hathaway said the STC fix approved in March has been completed on nearly all active aircraft, adding, "we decided to roll it out at our cost to the fleet." All remaining aircraft are expected to be modified soon in conjunction with planned maintenance.

The FAA had not yet issued an emergency AD on May 7, but one was still expected—and likely to include completion of modifications authorized under the March STC as a means of compliance that would eliminate the need to deactivate the entire system. Hathaway said the company provided regulators with volumes of data and flight test videos to support approval of the fix. Tamarack also reviewed attitude heading and reference system data from the flight that prompted the emergency AD in Europe, though the company is not yet allowed to make that data public.

“It certainly validates what we had suspected,” Hathaway said. “We’re eager to release that data at the appropriate time.”

Tamarack’s active winglet system has become a popular retrofit across the Citation fleet, with benefits including fuel savings, improved performance, and increased aircraft value.