In economics and business decision-making, a sunk cost is a retrospective (past) cost that has already been incurred and cannot be recovered. Sunk costs are sometimes contrasted with prospective costs, which are future costs that may be incurred or changed if an action is taken.........
ORAC, thanks for the economics lesson. I agree the RTM's are a
sunk cost but they also mean that we could avoid the
prospective cost of purchasing new engines.