Definition
A unit of frequency equal to one billion (1,000,000,000) cycles per second. In modern usage, this is called a gigahertz (GHz). One gigacycle equals 1,000 megacycles.
Plain English
A measure of how fast something repeats, equal to one billion times per second. It is an older name for what we now call a gigahertz.
Context Anchor
Seen in older aviation electronics, radio, and radar references; modern sources usually use gigahertz instead.
Derivation
From the Greek 'gigas' meaning 'giant,' used as a metric prefix for one billion, combined with 'cycle,' meaning one complete repetition of a wave. The term was replaced by 'gigahertz' when the international standard adopted 'hertz' as the unit name for cycles per second.
Why Pilots Care
Radar altimeters, weather radar, GPS, and satellite systems all operate in the gigacycle (gigahertz) range. Recognizing the term in older manuals or charts helps avoid confusion when comparing equipment specifications.
Intuition Check
Do not read gigacycle as a special kind of aviation cycle. It simply means one billion cycles, usually one billion wave repeats per second when frequency is being discussed.
Example Sentence 1
The aircraft's radar altimeter operates at about 4.3 gigacycles, which today is more commonly written as 4.3 GHz.
Example Sentence 2
Technicians checked the transmitter output at several gigacycles during the preflight inspection.