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What i mean by structure is (different composite materials and aluminum).

What are the cons in terms of time required to test the full body of the aircraft (B747 for example) in C and D checks ?

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Ultrasonic inspection is perhaps the most widely used inspection procedures in aerospace to detect subsurface anomalies.

  • Portability- A number of portable ultrasonic equipment are available, which are very simple and are widely used.

  • The detection depth for flaws is far superior compared to most other NDT methods.

  • It can be used for detecting flaws even if only one surface of the part is accessible (simply use pulse echo method).

  • The results are more or less instantaneous- Usually there is no waiting time involved as the results are displayed in a screen.

  • The time required for preparation is very less; usually the part is cleaned and the couplant applied; after the inspection, it can simply be wiped off.

However, just like any other (NDT) method, this too has its own share of disadvantages:

  • It is very difficult to use this method for parts which are very thin- for e.g. the aircraft skin because of the dead zone, though this can be overcome by using higher frequencies or immersion technique; in most cases of aircraft checks, this may not be an option. Also, it cannot be used for irregular and non-homogeneous parts (At-least, not the portable methods).

  • The method does not detect flaws that are oriented parallel to the wave propagation.

  • The material must be characterized prior to inspection. As the returning signal is affected by attenuation within the material, comparisons can be made only if a similar (defective and good) specimen of same material is characterized first.

  • Usually, Ultrasonic method requires a trained operator for interpretation of the results.

As far a full aircraft is considered, only some critical parts are tested using ultrasonic (or other NDT) methods. There is no way to check the entire aircraft except by thorough visual inspection.

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