The CH-53 Sea Stallion, first entering service in 1966, is a heavy-lift helicopter designed with rotor blades capable of immense weight capacity. Early models utilized extruded aluminum spars, while later variants like the CH-53D transitioned to cold-formed titanium. Both designs faced the critical challenge of detecting tiny cracks in the metal before catastrophic failure occurred.

Detecting these cracks was relatively straightforward due to the blades' pressurized nitrogen system; a barber pole pressure indicator on the ground signaled leaks. However, identifying cracks inflight proved difficult. Modern automotive tire pressure monitoring systems were considered, but early 1960s electronics were unreliable for rotating components, and wiring through slip rings was deemed too complex.

The solution was the Inflight Blade Monitoring System (IBIS). This system utilizes a small amount of radioactive Strontium-90 embedded in the pressure indicator. As a beta emitter, the radiation is detectable by a Geiger counter in the cockpit, providing immediate warning of blade cracks without requiring batteries or electronics on the rotating blade.

This elegant, low-tech solution remains in use today, with newer CH-53 variants incorporating fiber optics for all-composite blades, while older models continue to rely on the nuclear option for safety.