Definition
An angular offset of the localizer course from the runway extended centerline, generally three degrees or less, used at certain airports where it is not possible to align the localizer antenna with the runway centerline due to terrain, obstructions, or other site limitations.
Plain English
The localizer signal that guides you to the runway is not pointing exactly straight down the runway. It is angled slightly off to one side, so following it lines you up close to, but not perfectly with, the runway.
Context Anchor
Seen on instrument approach charts and during approach briefings when the localizer course is not aligned with the runway.
Derivation
‘Localizer’ comes from the verb ‘localize,’ meaning to fix the position of something. ‘Offset’ means shifted away from a reference. Together: a localizer course shifted away from its normal reference, the runway centerline.
Why Pilots Care
The pilot must recognize that the final approach course will not lead straight to the runway and will require visual alignment before landing.
Grounding Statement
On final approach, following the localizer exactly may still leave the airplane pointed slightly across the runway instead of straight along it.
Intuition Check
Offset does not mean the localizer is broken or inaccurate. It means the published guidance course is intentionally angled away from the runway centerline.
Example Sentence 1
The approach plate noted a two-degree localizer offset, so the crew briefed a visual correction to centerline after breaking out of the clouds.
Example Sentence 2
Because of the localizer offset, the aircraft tracked the angled course until the runway was in sight.