"The crash of a critical legacy system at Comair is a classic risk management mistake ... the legacy system failed, bringing down the entire airline, canceling or delaying 3,900 flights, and stranding nearly 200,000 passengers. The network crash cost Comair and its parent company, Delta Air Lines, $20 million, damaged the airline's reputation and prompted an investigation by the Department of Transportation."
Executives stalled all attempts to replace the old crew scheduling system until eventually it failed in service. Reading between the lines of the story, however, it is not clear whether the proposed replacements would have presented even greater risks. Risk management decisions can be buggers.