By Rachel Tobin Ramos When Big Brown took on billions of dollars of debt in 2007 to buy some employees out of a union-run pension plan, it seemed like a good idea. Then the recession hit, hammering the fund. Recently, the company found itself dealing with concerns about its riskier debt strategy. UPS, long a conservative company that eschewed debt and risk, was given what would amount to a “yellow caution” flag by a credit rating agency in January. This was after the Sandy Springs-based company had a pension plan fall below the amount it would need to cover its obligations.