FAA Powerplant Written Practice Test

Which inspection method uses a dye that penetrates cracks in the surface of engine parts?

1. X-ray inspection

2. Dye penetrant inspection

3. Magnetic particle inspection

4. Ultrasonic testing

The correct answer is: Dye penetrant inspection

Dye penetrant inspection is a widely used non-destructive testing method that involves applying a liquid dye to the surface of engine components. When this dye is applied, it seeps into any surface-breaking cracks or discontinuities due to capillary action. After allowing sufficient time for the dye to penetrate, the excess dye is removed from the surface, and a developer is applied. The developer draws the penetrant out of the cracks, creating a visible contrast that highlights the defects against the surface of the part. This method is particularly effective for identifying small, surface-breaking flaws and is commonly used in aviation maintenance and inspections to ensure the integrity of critical engine components. The other inspection methods listed serve different purposes and operate on different principles. X-ray inspection utilizes radiation to view internal structures; magnetic particle inspection involves creating a magnetic field and applying ferromagnetic particles to identify surface and near-surface defects, particularly in iron and steel; ultrasonic testing utilizes high-frequency sound waves to detect internal and surface defects. Each method is valuable in its own right, but dye penetrant inspection is specifically designed to detect cracks on the surfaces of components.