How far apart do parallel ILS approaches have to be?

• A. 4300 ft
• B. 1500 ft
• C. 3500 ft
• D. 2500 ft

Answer: (D)

The main idea is how much lateral separation is needed to fly two independent parallel ILS approaches safely. Two parallel ILS approaches require enough distance so that each localizer’s guidance and the protected airspace for its final approach remain distinct. The minimum separation between the centerlines of the two approach corridors is 2,500 feet. This spacing provides separate signal patterns and approach paths, reducing the chance of interference between the two guidance signals and ensuring adequate lateral clearance as you descend on final. If the runways are closer than this, you wouldn’t have independent parallel ILS approaches under standard procedures, and you’d need to rely on different arrangements (such as sequencing or radar-monitored spacing) rather than true simultaneous independent approaches.