In a Service Bulletin issued May 3, winglet manufacturer Aviation Partners (API) instructed operators with winglet-equipped 800-series Hawkers modified by STC#ST01411SE to reduce maximum permissible altitude to 34,000 feet. “Several instances of aileron/wing oscillations have been reported on the Hawker 800 [series],” the company said. “Aviation Partners and the FAA consider this Service Bulletin to be a safety-related limitation until a design change to preclude the oscillations is developed and FAA approved.”

Aviation Partners COO Hank Thompson said that after meeting with the FAA to discuss these incidents, “We did a great deal of analysis using finite element modeling, refining it and putting different models on the aircraft until we were able to get a model that agreed with what was being reported in flight.” It found that rebalancing the ailerons to a new tolerance forward of the hinge line fixes the problem.

The company tested “every scenario and potential model,” he said, “and every one of them dampened out with our solution.” Aviation Partners will flight-test the solution and then submit documents to the FAA, after which operators will be able to rebalance their ailerons and remove the 34,000-foot restriction. This should be ready next month, Thompson said. The FAA will be issuing an Airworthiness Directive that mirrors the company’s Service Bulletin, he said.