Definition
A ground-based hyperbolic radio navigation system that determines an aircraft's position by measuring the phase difference between continuous low-frequency signals transmitted from a master station and three associated slave stations arranged in a chain. The receiver compares phase relationships to locate the aircraft along intersecting hyperbolic lines of position on a specially printed Decca chart.
Plain English
An older radio navigation system that figures out where an aircraft is by comparing the timing of signals from four ground stations working together. The pilot reads the position off a special chart.
Context Anchor
Seen in older navigation-system discussions and aviation history, especially when comparing earlier radio navigation methods with modern systems.
Derivation
Named after the Decca Record Company, which developed and operated the system in Britain during and after World War II. The name carries no technical meaning -- it is simply the parent company's name.
Why Pilots Care
Before GPS, it provided reliable position information for flights over water or in areas without other aids.
Intuition Check
Do not read “Decca” as a technical description of the method. It is the name of the system; the key idea is position-finding by comparing radio signals from fixed stations.
Example Sentence 1
Before GPS became widespread, some European operators relied on the Decca Navigation System for low-altitude position fixing.
Example Sentence 2
In the 1960s, many commercial aircraft used the Decca Navigation System for precise enroute navigation.