Delta Air Lines received a second stamp of approval from a credit-rating agency, another rare signal of stability in the financially volatile airline industry.

Fitch is the second rating agency to elevate Delta’s position to investment grade while its comparable U.S. peers, United Airlines and American Airlines, still lag behind in the junk bond category.

The rating is similar to an individual’s credit score. Lenders base interest rates and the airline’s ability to pay back debts on its investment status.

In a statement late Thursday, Fitch cited Atlanta-based Delta’s improved profits, free cash flow and its paying down of debt as reasons for the upgrade.

“Importantly, the ratings are based on Fitch’s projections of the company’s performance through the economic cycle,” the Fitch report said, adding that Delta’s improved balance sheets “will provide the company with sufficient financial flexibility to maintain an investment-grade credit profile in a period of economic stress.”

Delta received its first investment grade rating in February from Moody’s.

The company is the largest carrier at Minneapolis-St. Paul International Airport, where its market share exceeds 70 percent.

Delta employs more than 8,000 people in the Twin Cities.