Airbus's lawsuit against Seattle-based winglet specialist Aviation Partners follows a claim by the US company that the airframer should pay royalties over its own wing-tip design. The two sides had worked closely during a period when Airbus assessed the Aviation Partners blended winglet for the Airbus A320.

Aviation Partners filed the patent for its winglet in February 1993, and it was issued the following year, but Airbus has since created its own "sharklet" wing-tip, which it will offer to customers next year and which will become a standard fit on the re-engined A320neo.

"In written and oral communications with Airbus, [Aviation Partners] has stated repeatedly that Airbus's winglet design falls within the claims of [its] patent, and that Airbus must therefore pay [Aviation Partners] a royalty for its allegedly infringing design," the formal complaint states.

A320 sharklets

 © Airbus

The lawsuit, dated 1 December, has been brought before the US district court for the western district of Texas. Aviation Partners' original patent describes the blended winglet as featuring a "critical departure" from regular winglet designs, which are hampered by "sharp corners" and rapid changes in chord.

"The object of the present invention is to provide a winglet configuration concept which includes an efficient transition between the wing and the winglet, which maintains a near-optimum loading over a substantial range of operating conditions, thereby achieving the full drag-reduction potential of the wing-tip device," it said.

It added that the leading-edge curve provides a smooth, gradual chord variation and limits the leading-edge sweep to less than 65° - necessary to avoid vortex shedding, which would compromise surface loading and increase drag.

The Airbus lawsuit argued that Aviation Partners, by demanding royalties, is directly charging the airframer with infringing this patent. "[Aviation Partners'] threats are a significant hindrance to Airbus and, without an early resolution, place Airbus at a competitive disadvantage," it added. "Under all the circumstances, [Aviation Partners'] threats and actions show that it is prepared and willing to enforce [its] patent against Airbus and that there is substantial live controversy between [the two companies], having adverse legal interests of sufficient immediacy to warrant the issuance of a declaratory judgement."

Aviation Partners said it was "surprised" at the legal action by Airbus, particularly given the previous close co-operation between them during tests of the US company's winglets on A320s. It added that it would "vigorously protect" its patented technology.

Source: Flight International