European regulators issued an emergency airworthiness directive April 19 requiring Tamarack’s active winglets, installed as a retrofit on nearly 100 Cessna Citation jets, to be deactivated before further flight, though the FAA did not immediately follow suit. A fix has already been approved, and the company is covering the cost.
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 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.”