"Boeing has been working closely and continuously with our suppliers since being notified of the issue to ensure timely and appropriate action, including comprehensive inspections and analysis throughout our supply chain," the company said in an email.
Kobe Steel said it discovered the violations during internal inspections and "emergency quality audits."
Product quality scandals have posed a challenge to the image of top Japan's manufacturers in recent years. In one of the largest, auto parts maker Takata Corp. has paid $1 billion in penalties for concealing an air bag defect blamed for at least 19 deaths worldwide. Major automakers are also engaged in massive recalls and facing criticism for allegedly continuing to use the defective air bags despite knowing of the problem.
Last year, Mitsubishi Motors Corp. acknowledged it had systematically falsified mileage data on some of its vehicles. That company's reputation was hammered earlier by a massive, systematic and decades-long cover-up of defects that surfaced in the early 2000s.
In another major case, materials and chemicals maker Asahi Kasei Corp. found data had been manipulated in 360 projects out of 3,052, casting doubts on the strength of construction pilings.