Dependent Parallel Approaches
Dependent parallel approaches are instrument approach procedures used at airports with parallel runway configurations, allowing two aircraft to conduct simultaneous arrivals with prescribed separation requirements. These procedures are classified as *dependent* because air traffic controllers must ensure specific lateral or diagonal spacing is maintained between aircraft operating on adjacent final approach paths. Unlike independent parallel approaches, which operate autonomously, dependent parallel approaches rely on coordinated sequencing and longitudinal management of arriving traffic.
Under standard FAA criteria, dependent approaches typically require a minimum of 1.0 nautical mile diagonal spacing between aircraft established on final approach courses. This diagonal distance accounts for both lateral and longitudinal separation components and is applied as a conflict-avoidance buffer between streams of aircraft converging on parallel runways. Spacing requirements may vary depending on local airspace structure, aircraft category mix, surveillance system capabilities, and weather conditions.
To execute dependent parallel approaches safely, high-fidelity radar systems or equivalent surveillance tools are essential. Controllers actively monitor both approach paths and issue speed adjustments or heading corrections as needed to maintain required intervals. In some terminal environments, controllers may issue staggered clearances or delayed descent instructions to ensure proper spacing is established well in advance of the final approach fix (FAF).
These procedures are commonly implemented at high-capacity commercial airports such as Atlanta (ATL), Dallas/Fort Worth (DFW), and Chicago O'Hare (ORD), where multiple parallel runways are used to optimize throughput. Dependent parallel approaches offer a balance between safety and capacity, enabling increased arrival rates without the full procedural separation required in independent operations. They are especially effective during peak traffic flows, adverse weather, or runway construction constraints, when maximizing available runway access is critical.
