Borrowing costs have become compelling, as markets are already pricing in expectations for reduced interest rates. And several external factors could reverse that trend.

"If you don't believe there are assets to replace your existing, you're going to be more willing to do a leveraging transaction like using first lien to take out a second lien."

Planemaker's top seven banks are providing support as costs of grounding the 737 Max total an estimated $18 million.

Company is using two $6 billion term loans and a $2 billion revolver to support purchase of Vodafone's stake in Verizon Wireless.