Definition
The set of transmitting antennas on the ground that produce the localizer signal for an Instrument Landing System (ILS). The array is positioned on the centerline of the runway, beyond the stop end, and radiates two overlapping signals on either side of the extended runway centerline. An aircraft's ILS receiver compares the strength of these two signals to determine whether the aircraft is left of, right of, or on the centerline during an instrument approach.
Plain English
A row of antennas placed past the far end of the runway that beams a signal back toward approaching aircraft. The signal tells the aircraft whether it is lined up with the runway centerline or drifting off to one side.
Context Anchor
Seen in instrument landing system discussions, especially when describing the localizer equipment located near the runway.
Derivation
Localizer comes from 'local,' meaning 'of a place' — the antenna locates the aircraft relative to a specific runway centerline. 'Array' means an organized arrangement of similar items, here referring to the row of individual antennas working together as one transmitter.
Why Pilots Care
It supplies the lateral guidance signal that keeps the aircraft aligned with the runway centerline during low-visibility approaches.
Grounding Statement
Picture a group of antennas past the runway end sending an invisible centerline path back toward arriving aircraft.
Intuition Check
Do not think of this as the cockpit display. The LOC ground antenna array is the airport equipment on the ground that sends the signal the cockpit instrument receives.
Example Sentence 1
On the airport diagram, the LOC ground antenna array is shown roughly 1,000 feet beyond the departure end of Runway 27.
Example Sentence 2
Maintenance crews inspect the LOC ground antenna array regularly to ensure signal accuracy for arriving aircraft.