Lots of free cash flow is the secret to carrying a lot of debt, that's why companies that have reliable free cash flow in good times and in bad like a Coke or a Proctor and Gamble for instance can get away with it if they need to. The airlines are the most cyclical industry there is and highly sensitive to the economy, a downturn that results in negative FCF can be a disaster for highly indebted companies. This is why in the 1990's we saw companies like UAL making 1B+ a year in profits in a good economy filing for bankruptcy a few years later when their liabilities overwhelmed them.
As long as DAL can continue as they are operating now with strong FCF to service/pay down the debt they will be fine. Unfortunately, what we find in the airline industry is that the good times tend to be short lived. Imagine what would happen if, say, Israel attacks Iran and the cost of fuel doubles causing all the airlines to have negative FCF? This is the problem with high debt in any industry but in particular the airline industry because of it's hyper-sensitivity to the economy and huge exposure to fuel cost risk.
Note for the General, this is not Delta bashing but rather an attempt to temper your optimism with some realism. UAL pilots in the late 1990's sounded just like you do now. DAL has a lot of debt....period. If they meet all of their debt reduction targets they will still have a lot of debt. If the current industry conditions continue they will be fine, if anything bad happens they will run out of options quickly. We've seen this cycle repeat over and over again in this industry.
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