Definition
A nondestructive inspection technique in which a short burst of high-frequency sound waves is sent into a part from a single transducer, and the same transducer then listens for the sound to bounce back. The time it takes for the echo to return, and the strength of that echo, reveals the location of cracks, voids, or other internal flaws, as well as the thickness of the material.
Plain English
You press a small probe against the part. The probe sends a quick pulse of sound into the metal, then listens for the echo. If the sound bounces back early or in an unexpected pattern, there is a flaw inside the part.
Context Anchor
Seen in aircraft maintenance when metal parts, engine parts, welds, or structural areas need to be checked for hidden internal damage.
Derivation
Pulse from Latin pulsus, meaning a beat or push -- here, a short burst of sound. Echo from Greek echo, the return of a sound. Ultrasonic combines Latin ultra (beyond) with sonic (sound), meaning sound at frequencies above what humans can hear. Together: a short sound pulse is sent in, and its echo is read back.
Why Pilots Care
Reveals internal damage that could lead to structural failure in flight while leaving the part undamaged for continued service.
Analogy
It works like sonar on a submarine. A pulse of sound goes out, bounces off something, and the time it takes to return tells you how far away that something is and roughly what it looks like.
Intuition Check
Do not picture an ordinary audible echo in a room. In this inspection method, the echo is a returning high-frequency sound signal inside the material, usually shown on an inspection instrument.
Example Sentence 1
The mechanic used the pulse-echo method of ultrasonic inspection to check the propeller hub for internal cracks before signing off the annual.
Example Sentence 2
During the annual inspection the technician used pulse-echo ultrasonic inspection on the propeller hub to confirm there were no internal cracks.