Finish Cracking of Composite Flight Control Surfaces

A request from a commercial airline to analyze severe finish cracking of carbon-fiber composite control surfaces initiated an investigation by Boeing, in cooperation with the inquiring airline, into the significance of the cracking to the structural integrity of the composite substrate. The investigation, involved the basic mechanisms of the finish cracking, as well as development of acceptable re-work options for the airline. The results indicated that finish-cracked parts were structurally sound, however they should be refurbished to prevent secondary environmental degradation from the loss of the protective finish by flaking and erosion. The study resulted in new guidelines for finish system applications, as well as a new perspective on finish appearance criteria.