Credit ratings go down with the economy.

While companies can survive economic storms with strong balance sheets, a growing number in South Florida are suffering damage to their credit ratings.

And for those operating in aviation, tourism and other sectors hit by the Sept. 11 attacks, pre-existing problems seem to be worsening.

Mastec (NYSE: MTZ), ANC Rental Corp. (Nasdaq: ANCX), Kellstrom Industries (Nasdaq: KELL), Carnival Corp. (NYSE: CCL), Royal Caribbean (NYSE: RCL) and Orius Corp. are among those .whose credit ratings have been questioned by Standard and Poor's (S&P).

At Kelistrom Industries' Miramar headquarters, CEO Zivi Nedivi is working with lenders and has hired financial advisers to help convert his company's corporate bonds. He said his jet engine overhauling business is taking a proactive approach to the doldrums in the airline sector by turning shareholder notes into equity.

"We had a problem with our sheet to start with prior to the Sept. 11 events, and following the events the details became more intensive," Nedivisaid.

S&P lowered Kellstrom's credit ratings to "negative" on Aug.17. Liquidity concerns, poor financial performance and non-compliance on credit agreements with senior lenders were cited as weaknesses. Its biggest credit line was decreased until, an interest payment due Oct. 15 on certain notes was made. That money never came in, prompting another S&P downgrade last Thursday.

The company is restructuring its convertible and mezzanine bonds.

"For us to have any reasonable balance sheet, the bonds have to be converted 100 percent to equity:" Nedivi said.

Coming up with the money to pay lenders hasn't been easy for many companies, either before or …