Onex Partners is reducing its stake in Spirit AeroSystems (NYSE: SPR) through a secondary offering of about 10.3 million shares of the company's class A common stock. Morgan Stanley is acting as underwriter. Other sellers in the offering include members of company management, but the company itself, which manufactures commercial aerostructures, will not be selling any shares. Onex acquired the company in a 2005 LBO and took it public the following year. The firm will continue to hold voting control of Spirit post-transaction.