What it is

Interval Management (IM) uses ADS-B In capabilities to precisely manage spacing between aircraft. IM is a component of the future Trajectory Based Operations (TBO) vision, where air traffic controllers may opt to provide IM clearances to flights to manage their spacing intervals relative to other aircraft. Flight-deck applications, like IM, can provide more precise spacing than ground-based decision support tools alone, providing greater TBO benefits.

Interval Management operations involve controllers using automation systems at air traffic facilities, to pre-condition traffic and identify opportunities for IM clearances. A controller then authorizes the flight crew to use the ADS-B In avionics, which provide speed guidance to precisely achieve and maintain an ATC-issued spacing interval (in time or distance) relative to a lead aircraft. The speed guidance is frequently calculated to respond to unexpected behavior by the lead aircraft or wind changes, for example.

Benefits

• Improved arrival throughput through more precise and consistent spacing during arrival and approach operations.
• Maintaining efficient flight paths during high-density traffic periods.
• Reduced fuel burn, noise, and emissions when flights stay on their planned Performance Based Navigation (PBN) flight paths.
• Decreased system delays.

An operational evaluation of an initial IM avionics capability occurred from November 2022 to November 2024 for operations in Albuquerque Center’s airspace, with an emphasis on arrivals into Phoenix airport. The FAA worked with American Airlines and ACSS to gather data and analyze results, which showed the spacing precision claimed in prior studies was achieved in a real-world environment. The IM spacing performance was significantly better than what can be achieved using time-based metering decision support tools and controller-issued speed instructions alone. Prior studies showed that increased spacing precision at arrival meter fixes, like those operations studied as a part of this operational evaluation, can lead to flight efficiency benefits because flights are better able to remain on their planned arrival procedures. For more details, see the AIRS I-IM Operational Evaluation Final Report.

Availability

IM standards are complete and ready for manufacturers to produce the necessary avionics (see FAA Technical Standard Order - C195c). FAA guidance regarding IM operations exists in Advisory Circular 90-114C. FAA ATC automation systems will need software modifications to support controllers in initiating and monitoring IM operations.

How it Works

Interval Management consists of a set of ground and flight-deck capabilities and procedures that are used in combination by air traffic controllers and flight crews to more efficiently and precisely manage spacing between aircraft in traffic flows. IM operations can be used in en route and terminal airspace. 

During an Interval Management operation, the controller will instruct the flight crew to achieve and maintain a spacing goal relative to a lead aircraft, and the flight crew will follow the speed guidance provided by the avionics. The avionics and automation systems will support IM operations to the same runway, parallel runways, and crossing & converging runways, enabling increased arrival throughput.