I didn't notice anything in the bond indenture about collateral and haven't read anything that I can recall from the financial statements that stated that the equipment was encumbered as collateral for any loans/bonds/etc.

The bondholders would have to pursue their legal action in order to attain such a position, which they are not doing at present. IMO they are not pursing it because they do not have a winning position at this time. The business judgment rule trumps their arguments until KRY missed an interest payment, which under the indenture would accelerate the maturity.