Definition
A type of simultaneous instrument approach procedure used at airports with closely spaced parallel runways that are too close together to permit standard simultaneous independent ILS approaches. One runway is served by a straight-in ILS approach, while the other is served by an offset approach (typically an LDA with glideslope) whose final approach course is angled a few degrees away from the parallel runway centerline. The offset reduces the risk of collision between aircraft on the two final approach courses and allows both arrivals to proceed simultaneously under PRM (Precision Runway Monitor) surveillance.
Plain English
A way of landing two airplanes at the same time on two runways that sit very close together. One airplane flies straight in to its runway. The other flies an approach that is angled slightly off to the side until it gets close to the airport, then turns to line up with its runway. The angle keeps the two airplanes safely apart while they are still in the clouds.
Context Anchor
Pilots encounter SOIA on published approach procedures, in approach briefings, and in clearances for certain airports with closely spaced parallel runways.
Derivation
The name describes the procedure directly. 'Simultaneous' means both approaches happen at the same time. 'Offset' refers to the fact that one of the final approach courses is intentionally angled away from its runway centerline rather than aligned with it. 'Instrument Approaches' means both are flown using published instrument procedures.
Why Pilots Care
Allows higher arrival rates at airports with closely spaced parallel runways while preserving required safety separation under instrument conditions.
Grounding Statement
Picture two airplanes approaching side-by-side runways, with one airplane kept on a slightly angled path until it can safely finish the landing visually.
Intuition Check
Offset does not mean the airplane lands while still angled away from the runway. Here, offset means the approach path is intentionally angled at first, then the pilot aligns with the runway visually when the procedure allows it.
Example Sentence 1
Approaching San Francisco in marginal weather, the crew reviewed the SOIA briefing and confirmed they were current on PRM procedures before accepting the offset LDA to runway 28L.
Example Sentence 2
During the SOIA the crew monitored the Precision Runway Monitor display to confirm the offset path remained within protected airspace.