Definition
A nondestructive inspection technique used to detect cracks or other surface flaws in propeller blades and similar components by applying a dye penetrant and a developer, then examining the surface for indications of defects. Often abbreviated BIM, it is most commonly associated with checking metal propeller blades for hidden damage.
Plain English
A way of checking propeller blades for tiny cracks you cannot see with the naked eye, by applying a special liquid that seeps into any crack and then makes the crack visible.
Context Anchor
Seen during helicopter preflight inspections, maintenance checks, and rotor blade condition inspections.
Why Pilots Care
Confirms the blades remain airworthy and reduces the chance of failure during flight.
Analogy
It is similar to checking a tire for a slow leak. If it cannot hold pressure, something may be wrong even if the outside still looks normal.
Intuition Check
Do not assume this means simply looking over a blade by eye. In this context, the inspection depends on whether the blade can hold internal pressure.
Example Sentence 1
The mechanic used the blade inspection method to check the propeller for hidden cracks before returning the aircraft to service.
Example Sentence 2
Following the blade inspection method, the technician measured each rotor blade for any change in shape or balance.