The Helicopter with Radioactive Blades

The CH-53 Sea Stallion helicopter uses an ingenious system called IBIS to detect cracks in its rotor blades during flight by pressurizing them with nitrogen gas and exposing a small amount of radioactive Strontium-90 that emits beta radiation detectable by a Geiger counter in the cockpit. This elegant mechanical solution, which requires no batteries or electronics on the rotating blades, has proven so effective that it remains in use today on older CH-53 variants, while newer models have upgraded to fiber optic detection systems.