I didn't stay at a Holiday Inn Express last night, but I do have an MBA, so I'll throw in my .02. Debt to Equity (D/E) is the ratio used to measure long term debt. When put into ratio form it allows for a common sized comparison of debt across differen sized companies.
A couple other handy ratios are:
Current Ratio = Current Assets / Current Liabilities
Quick Ratio = Quick Assets / Current Liabilities
The current ratio is a measure of a company's ability to meet short term (12 mos.) expenses. The Quick Ratio is a acid test version that doesn't include inventory in the Current Assets calculation. Generally a 2:1 current ratio and a 1:1 quick ratio are reaonable. I'm not sure about airline industry specifics.
When looking at the Debt to Equity (D/E) ratios a bigger factor is the trend in the ratio over time vs. a balance sheet snapshot. If a company can reduce the long term D/E ratio while maintaining cash the balance sheet is improving.
These links will give you a snapshot of company financials
UAUA
http://finance.yahoo.com/q/bs?s=UAUA&annual
CAL
http://finance.yahoo.com/q/bs?s=cal
NWA
http://finance.yahoo.com/q/bs?s=NWACQ.PK&annual
SWA
http://finance.yahoo.com/q/bs?s=luv
DAL - Not available, but should be once they start trading again.