FAA Powerplant Written Practice Test

What method is commonly used to test a steel propeller hub for cracks?

1. Visual inspection

2. Magnetic particle inspection

3. X-ray inspection

4. Ultrasonic inspection

The correct answer is: Magnetic particle inspection

Magnetic particle inspection is a widely accepted method for detecting surface and slightly subsurface cracks in ferromagnetic materials, such as a steel propeller hub. This non-destructive testing technique works by magnetizing the steel and applying fine magnetic particles, typically in a liquid suspension. When the particles encounter a crack or irregularity in the metal, they cluster around the defect, making it visible to the inspector. This method is particularly effective because it can reveal discontinuities that may not be seen through visual inspection alone and is fast and relatively easy to perform. Visual inspection, while useful for identifying obvious surface defects, is limited in its ability to detect hidden cracks. X-ray inspection, although effective for internal structures and complex geometries, can be less practical and more time-consuming for field tests of large components like propeller hubs. Ultrasonic inspection is also valuable for detecting internal flaws, but it typically requires more technical skill and equipment than magnetic particle inspection and is not as effective for surface cracks in ferromagnetic materials.