Boeing Co. sold new bonds to help repay nearly $3 billion of debt, announcing the sale just minutes after a downgrade to the company's credit rating.

The planemaker issued $4.9 billion of unsecured notes in four parts, according to a person with knowledge of the matter. The debt sale was announced in a filing earlier Thursday, just minutes after Fitch Ratings put out a report cutting Boeing one notch to BBB-, the lowest investment-grade rating, with a negative outlook.

The proceeds of the sale will help repay $2.8 billion of debt, which is either in the form of commercial paper or term bonds due next year. The longest portion of the offering, a 10-year security, will yield 280 basis points (bps) over Treasuries, after initial discussions had pegged it at around 300 bps, said the person, who asked not to be identified as the details are private.