Aviation Training Experts™

handbook

Aviation Maintenance Technician Handbook–General

FAA-H-8083-30B Version 2023
All Library Documents

Chapter 10

Inspection Concepts & Techniques

Ultrasonic Instruments

A portable, battery-powered ultrasonic instrument is used for field inspection of airplane structure. The instrument generates an ultrasonic pulse, detects and amplifies the returning echo, and displays the detected signal on a CRT or similar display. Piezoelectric transducers produce longitudinal or shear waves, the most commonly used waveforms for aircraft structural inspection.

Reference Standards

Reference standards are used to calibrate the ultrasonic instrument. Reference standards serve two purposes: to provide an ultrasonic response pattern that is related to the part being inspected and to establish the required inspection sensitivity. To obtain a representative response pattern, the reference standard configuration is the same as that of the test structure or is a configuration that provides an ultrasonic response pattern representative of the test structure. The reference standard contains a simulated defect (notch) that is positioned to provide a calibration signal representative of the expected defect. The notch size is chosen to establish inspection sensitivity (response to the expected defect size). The inspection procedure gives a detailed description of the required reference standard.

Couplants

Inspection with ultrasonics is limited to the part in contact with the transducer. A layer of couplant is required to couple the transducer to the test piece, because ultrasonic energy does not travel through air. Some typical couplants used are water, glycerin, motor oils, and grease.

Inspection of Bonded Structures

Ultrasonic inspection is finding increasing application in aircraft bonded construction and repair. Many configurations and types of bonded structures are in use in aircraft. All of these variations complicate the application of ultrasonic inspections. An inspection method that works well on one part or one area of the part may not be applicable for different parts or areas of the same part. Some of the variables in the types of bonded structures are as follows:

  • Top skin material is made from different materials and thickness
  • Different types and thickness of adhesives are used in bonded structures
Figure 10-19. Through-transmission and pulse echo indications.
Figure 10-19. Through-transmission and pulse echo indications.
Figure 10-20. Block diagram of basic pulse-echo system.
Figure 10-20. Block diagram of basic pulse-echo system.
Figure 10-21. Pulse-echo display in relationship to flaw detection.
Figure 10-21. Pulse-echo display in relationship to flaw detection.
Figure 10-22. Pulse-echo angle beam testing.
Figure 10-22. Pulse-echo angle beam testing.

and thickness, doublers (material and thickness), closure member attachments, foam adhesive, steps in skins, internal ribs, and laminates (number of layers, layer thickness, and layer material)

  • The top only or top and bottom skin of a bonded structure may be accessible

Types of Defects

Defects can be separated into five general types to represent the various areas of bonded and laminate structures as follows:

  1. Type I—disbonds or voids in an outer skin-to-adhesive interface.

It is necessary that the frequency of the ultrasonic

  1. Type II—disbonds or voids at the adhesive-to-core