During recent years, with the introduction of more complex aircraft structures, new techniques of aircraft servicing have been needed. It is essential to find even the smallest defects at a very early stage, but costly strip-examination must be avoided so far as possible.

Non-destructive testing is now playing an important part in this field, but many aeronautical engineers are unaware of the capabilities and limitations of the main methods.

This paper sets out to explain the basic principles of radiography, ultrasonic testing and eddy current testing. Since sampling inspections using these methods are now a mandatory requirement on all civil aircraft the paper should be of interest to all readers.