The airline is raising cash ahead of a potential downturn.JetBlue Airways (JBLU 1.52%) charted a course for the debt market this week, raising more than $3 billion through a series of three deals.The money raised will be useful to refinance some debt coming due in the years to come and as a cushion against a potential downturn. But it also changes the airline's leverage profile. Investors are concerned, sending JetBlue shares down 22% for the week as of Thursday afternoon, according to data provided by S&P ...