A T-shirt definition of the word “helicopter” reads that the aircraft is: “A million parts rotating rapidly around an oil leak waiting for metal fatigue to set in.” While it may be a bit of an exaggeration, there are few machines in the world with so many rapidly spinning components—components that, when they spin erroneously, can cause catastrophic failures. Monitoring these components has been the job of helicopter Health and Usage and Monitoring Systems (HUMS). Born from tragedy over 30 years ago, HUMS has come a long way.