It's not necessarily about taking debt to buyback their stock. It is about free cash flow. Here are some facts:

"As a group, the six [major US] airlines spent 96% of their free cash flow on stock buybacks over the past 10 full years through 2019."

"Boeing’s free cash flow for 10 years totaled $58.37 billion, while the company spent $43.44 billion, or 74% of free cash flow, on stock repurchases."