NEW YORK — Delta Air Lines Inc. is planning to refinance debt on some of its older planes, including Airbus A320s it got when it bought Northwest Airlines.

The new debt will be backed by 31 of its older planes. They include 16 Airbus A319s and A320s bought by Northwest between 1998 and 2002. The deal also includes 14 Boeing 767s bought by Delta between 1995 and 2000, as well as a 757, according to a rating issued Wednesday by Moody’s Investors Service.

The new debt will replace borrowing that would have come due in 2019 and 2020.

The planes are an average of 12.4 years old, making them the oldest to be used as collateral on recent aircraft debt of this type, Moody’s wrote. It rated some of the debt at “Baa2,” meaning it has “moderate credit risk” and has speculative characteristics, according to Moody’s. Another batch of the debt was rated at “Ba3,” which has “speculative elements and are subject to substantial credit risk.”

Delta shares rose a penny to $11.15 in afternoon trading. They are near the upper end of their 52-week range of $6.41 to $12.25 per share.