FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesHard
A technician suspects a subsurface flaw located deep within a thick aluminum landing gear forging, undetectable by eddy current or liquid penetrant methods. Which nondestructive inspection method uses high-frequency sound waves transmitted through a couplant to detect internal discontinuities at varying depths within the material?
- AMagnetic particle inspection
- BUltrasonic inspection
- CRadiographic inspection
- DLiquid penetrant inspection
Show answer & explanationAnswer & explanation
Correct answer: B. Ultrasonic inspection
Ultrasonic inspection sends high-frequency sound pulses into a material through a couplant (such as gel or water); reflections from internal flaws or the back surface are analyzed on a display to locate and size discontinuities at specific depths. Magnetic particle and liquid penetrant only detect surface or near-surface flaws, and while radiography also finds internal flaws, it uses X-rays or gamma rays rather than sound waves and does not require a couplant.
Why the other options are wrong
- A. Magnetic particle inspection only detects surface and near-surface flaws in ferromagnetic materials.
- C. Radiography uses penetrating radiation, not sound waves and couplant, though it also finds internal flaws.
- D. Liquid penetrant inspection only reveals flaws open to the surface.
Ultrasonic Inspection
An NDI method using high-frequency sound waves transmitted through a couplant to detect and locate internal or surface flaws at specific depths within a material.
- Uses pulse-echo or through-transmission techniques
- Requires a couplant (gel, oil, or water) to transmit sound into the part
- Can precisely locate flaw depth, unlike radiography which shows a 2D projection
Memory trick: Ultrasonic SHOUTS sound waves deep into metal to find hidden flaws