What you're seeing in increasing debt is due to their change and financial reporting. They added plane leasing cost to their liabilities with a corresponding increase change to the asset.
Increasing debt due to a new line item in the balance sheet of 8.1 billion called operating lease liability. They offset was 9.4 billion operating right of use lease asset.
Did you get those numbers from yahoo finance? I saw the same thing, but you also need to consider that the enterprise value also went up from $34B to $46B, and a lot of other sites still show the debt around $24B and they actually paid some off. Also, cash on hand is actually closer to $7.5B not $4.76B. Looks like those numbers are off somewhere. Like stock said they modified their approach to their numbers. BTW they have more cash on hand than UAL & DAL too. Their cash to debt ratio is actually better if I am not mistaken.