Definition
Instrument approach procedures that use a Localizer-type Directional Aid for lateral guidance. An LDA provides course guidance similar in accuracy to an ILS localizer, but the course is not aligned with the runway centerline. When the offset from runway centerline is 30 degrees or less and the procedure includes straight-in minimums, a straight-in landing may be authorized; otherwise, only circling minimums are published. Some LDA approaches include glideslope guidance, but most do not.
Plain English
An instrument approach that uses a precise side-to-side guidance signal to bring you close to the airport, but the signal does not point straight down the runway. You fly the course toward the airport, then maneuver visually to land.
Context Anchor
You will see LDA approaches on instrument approach charts and hear them assigned by air traffic control when that is the published procedure for an airport.
Derivation
Localizer-type Directional Aid. The name signals that the equipment behaves like an ILS localizer (the lateral-guidance part of an ILS) but is used as a directional aid because it does not line up with the runway. Knowing this tells you to expect localizer-quality precision laterally, but not a runway-aligned final.
Why Pilots Care
LDA approaches provide a published instrument procedure to runways where terrain or obstacles prevent a straight-in localizer alignment, increasing access to the airport in low visibility.
Intuition Check
Do not assume an LDA approach points straight down the runway. It gives localizer-like guidance, but the course may be angled away from the runway centerline.
Example Sentence 1
Because of the mountains east of the field, the only published instrument procedure is one of the LDA approaches, which ends with a short visual segment to align with the runway.
Example Sentence 2
Because the LDA was offset, the crew completed the turn to final inside the final approach fix.