Definition
Sound-wave frequencies above the upper limit of human hearing, generally considered to be above 20,000 hertz (20 kHz). In aviation, ultrasonic frequencies are used in nondestructive testing equipment to detect cracks, voids, and other internal flaws in aircraft structures and components.
Plain English
Sound waves too high-pitched for people to hear, used by special equipment to look inside metal parts for hidden cracks or damage.
Context Anchor
Seen in aircraft maintenance and inspection discussions, especially when checking parts for hidden internal damage.
Derivation
From Latin 'ultra' meaning 'beyond' and 'sonus' meaning 'sound.' Literally 'beyond sound' -- meaning beyond the range of sound the human ear can pick up.
Why Pilots Care
Allows inspectors to identify internal defects in critical airframe and engine parts without disassembly or damage, preserving structural safety.
Analogy
A dog whistle is a simple example: people may not hear it, but the sound is still there. Ultrasonic inspection uses sound that is too high for people to hear, but the equipment can still measure how it travels through a part.
Intuition Check
Ultrasonic does not mean very loud. It means the sound frequency is higher than normal human hearing.
Example Sentence 1
The mechanic used ultrasonic frequencies to inspect the propeller blade for internal cracks before returning the aircraft to service.
Example Sentence 2
Ultrasonic frequencies revealed a small void inside the turbine blade during the overhaul inspection.