# Parallel Instrument Runway Operations: Independent, Dependent, and Segregated Modes

> Review operational modes for parallel or near-parallel instrument runways, including NTZ requirements and localizer interception constraints.

- **Subject:** 010 — Air Law
- **Section:** 010-06 — Aircraft Operations
- **Topic code:** 010-06-07
- **Last reviewed:** 2026-03-27
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/air-law/aircraft-operations/parallel-or-near-parallel-instrument-rwys-icao-doc-8168-volume-i/

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Simultaneous operations on parallel instrument runways require specific procedures and separation.

## Modes of Operation

1.  **Mode 1 - Independent Parallel Approaches**:
    *   Simultaneous approaches to parallel runways where **radar separation minima are not prescribed** between aircraft on adjacent centerlines.
    *   Requires a **No Transgression Zone (NTZ)**.
2.  **Mode 2 - Dependent Parallel Approaches**:
    *   Simultaneous approaches where **radar separation minima are prescribed** (diagonal) between aircraft on adjacent runways.
    *   Requires procedures like divergent missed approach turns (30°).
3.  **Mode 3 - Independent Parallel Departures**:
    *   Simultaneous departures in the same direction.
    *   Runway centerlines must be separated by a minimum (e.g., 760 m).
    *   Departure tracks must **diverge** immediately after takeoff (minimum **15°**).
4.  **Mode 4 - Segregated Operations**:
    *   One runway is used exclusively for approaches and the other for departures.

*   **Mixed Operations**: Approaches and departures mixed on both runways.
*   **Semi-mixed Operations**: One runway exclusive (departures or arrivals) and the other mixed.

## Technical Requirements

### No Transgression Zone (NTZ)
*   Airspace corridor at least **610 m (2000 ft)** wide.
*   Located centrally between the extended runway centerlines.
*   **Fundamental in independent approaches**.
*   If an aircraft penetrates the NTZ, the controller must intervene immediately to maneuver any threatened aircraft on the adjacent approach.

### Localizer Interception (ILS/MLS)
In independent parallel approaches:
*   Interception angle: **Maximum 30°**.
*   Straight and level flight prior to interception: At least **2 km (1.0 NM)**.
*   Established on the localizer: At least **3.7 km (2.0 NM)** before intercepting the glide path.

### Suspensions
Independent parallel approaches may be suspended under certain meteorological conditions (crosswind, turbulence, wind shear) that may increase track deviations towards the NTZ.

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