Aviation Partners, Inc. (API) will proceed with royalty claims against Airbus after the European airframer sought to dismiss claims the “sharklet” currently being tested on the Airbus A320 narrowbody breaches a 1994 patent on API’s own blended winglet design.

The lawsuit, filed by Airbus last week in a Texas District Court, in essence says API’s repeated claims for royalties are invalidated by three sections related to the right to patent a design and another distinguishing the specification of the winglet from the sharklet.

“API’s threats are a significant hindrance to Airbus and, without an early resolution, place Airbus at a competitive disadvantage,” says the airframer.

The winglet maker disputes this claim. “We are certainly surprised by the lawsuit attempting to invalidate our patent on blended winglets after working closely with Airbus over the past five years. We have had many meetings with their engineering group and top executives, both in America and Europe,” says API founder and CEO Joe Clark.

“We have built and flown patented blended winglets on the Airbus A320 in Toulouse. We have flown them on one of JetBlue [Airways’] A320s using JetBlue flight crews with excellent results achieved—a 5% fuel savings—all of this with the cooperation of Airbus.

“What I can tell you is that we will vigorously protect our patented technology and intellectual property, which is currently saving the world billions of gallons of fuel on Boeing, Dassault, Hawker and Gulfstream airplanes,” adds Clark.

Court filings are expected soon reiterating this defense; for now API is not commenting beyond Clark’s statement.

The lawsuit was filed one day after Airbus initiated a months-long test of its A320 sharklet with a five-hour initial flight from its Toulouse headquarters. At the time, Airbus said the sharklet is “designed to reduce fuel consumption by up to 3.5%, corresponding to an annual CO2 reduction of some 700 tonnes per aircraft, while also enhancing the payload/range and takeoff performance.”

Airbus added that the carbon fiber composites addition, which is about 2.5 meters (roughly 8 ft.) tall, replaces the current A320 wingtip fences that are smaller and of a modified triangular shape. Sharklets are standard on Airbus A320NEO family aircraft and are being offered as optional equipment on new-build baseline versions of its current generation of single-aisle aircraft.

A venture between API and Boeing, Aviation Partners Boeing (APB), has developed winglets for the U.S. airframer’s 737 family of narrowbodies. APB winglets also are available for Boeing’s 757, and a design program has been launched for the 767.