European safety regulators have urgently ordered the de-activation of a load-alleviation system on Textron Aviation Cessna CitationJets fitted with Tamarack Aerospace Group winglets.

The load-alleviation system, known as Atlas, is designed to offer superior performance to passive winglets by adapting to changing wing loads.

Atlas uses load sensors to control wing loading automatically during events such as wind gusts, and optimise the wing to improve efficiency during routine flight.

But the European Union Aviation Safety Agency is concerned over occurrences in which the Atlas system “appears to have malfunctioned”.

EASA says the resulting in-flight upsets, in some cases, led to pilots’ experiencing “difficulty to recover the [aircraft] to safe flight”.

“Investigation continues to determine the [cause or causes] for the reported events,” it adds, stating that the situation presents a loss-of-control risk.

EASA has issued an emergency airworthiness directive ordering the Tamarack Atlas to be de-activated and the active-control surfaces fixed in place, before the aircraft’s next flight.

The order affects the 525, 525A and 525B models of the Cessna CitationJet.

UK-based modifications specialist Cranfield Aerospace Solutions has published a service bulletin with instructions on pulling and collaring the Atlas circuit-breaker, to immobilise the active-control surfaces.

EASA has also ordered that aircraft flight manual supplements be amended to include new operational limitations and instructions for pre-flight inspections.

Within 100h operators should contact Cranfield Aerospace Solutions for instructions on modifying Atlas. Modification allows the Atlas to be re-activated and the limitations lifted.

EASA states, however that the emergency airworthiness directive is an interim measure, and further action may follow.