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Parallel Runway Traps

When simultaneous instrument approaches are being conducted to parallel runways, ATC employs a no-transgression zone (NTZ) of variable dimensions to monitor and ensure proper separation, as depicted below. The FAA's Aeronautical Information Manual has lots more detail on the various ways NTZs are implemented, which aren't really relevant to VFR pattern operations at either towered or non-towered airports.
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Key Takeaways:

  • Parallel runway configurations, particularly those with offset thresholds, are a significant and often overlooked contributing factor to "wrong-surface events" (WSEs) and runway incursions.
  • WSEs, where aircraft land or depart on the wrong runway or taxiway, occur nearly every other day and frequently involve general aviation, sometimes leading to fatal accidents like the mid-air collision at North Las Vegas Airport.
  • Mitigating risks at parallel runway airports requires pilots to thoroughly review airport layouts, actively listen and confirm ATC clearances, utilize electronic guidance, maintain vigilance for "see and avoid," and guard against expectation bias.
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Airports and their runways come in all shapes and sizes, from turf strips lacking any real markings, but with trees at both ends, to massive, busy, complicated affairs like ATL, DFW, JFK or ORD. And pilots are expected to understand and comply with all procedures for operating at them, including taxiways and hotspots, runway intersections, LAHSO (land and hold short operations), and even soft-field takeoffs and landings on unpaved surfaces. As too many close calls involving runway incursions and near-misses remind us, sometimes things don’t go as planned.

A lot of the incursions and near-misses involve single- or crossing-runway events—and pilot error right alongside ATC mistakes. The industry’s conversation about these events is ongoing, but doesn’t often consider a common airport configuration: parallel runways. That’s too bad, especially since that configuration likely was a contributing factor in a recent fatal mid-air.

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