What is the standard longitudinal separation required between DME-equipped and RNAV-equipped aircraft using ATD?

The standard longitudinal separation required between DME-equipped and RNAV-equipped aircraft using ATD is 20 miles. This separation standard is established to ensure safe and efficient management of aircraft in controlled airspace. The importance of this standard lies in the varying accuracy and reliability of the navigation systems involved. DME-equipped aircraft use distance measuring equipment to determine their position relative to a DME station, while RNAV-equipped aircraft rely on various navigation aids and onboard systems to maintain their flight path.

The 20-mile separation provides a necessary buffer that accounts for potential inaccuracies or variations in flight paths, allowing for better management of air traffic and minimizing the risk of conflicts between aircraft. This standard helps air traffic controllers maintain safe distances between differing navigation systems, which is critical for ensuring safety in crowded airspace.

Other separation distances, whether shorter or longer, would either not provide adequate safety margins for the differing navigation equipment's capabilities or may introduce unnecessary restrictions on traffic flow, reducing operational efficiency.