Definition
An air traffic control automation tool that calculates and issues speed advisories to controllers, who then pass them to pilots, in order to achieve and maintain a precise time-based or distance-based spacing interval between aircraft. The calculations are performed by ground systems using aircraft performance data, winds aloft, and trajectory predictions; the pilot's role is to fly the assigned speed when issued.
Plain English
A ground computer works out what speed each aircraft should fly so the planes stay properly spaced in line. The controller passes that speed to the pilot, and the pilot flies it.
Context Anchor
A pilot may encounter this term in air traffic control and arrival-spacing discussions, especially where controllers are using automation to manage the flow of aircraft into an airport.
Derivation
Interval Management' refers to managing the gap (interval) between successive aircraft. 'Ground Based' distinguishes this from cockpit-based interval management, where the calculation is done onboard the aircraft. Knowing this contrast helps: with GIM-S, the work happens on the ground and the pilot just flies the speed.
Why Pilots Care
Enables pilots to make small speed adjustments early, reducing the chance of being vectored off the arrival or having to make large thrust changes later.
Grounding Statement
Picture several aircraft lining up to land, with ATC using a computer-generated speed suggestion to keep each aircraft properly spaced behind the one ahead.
Intuition Check
“Advisory” does not mean the pilot can ignore an ATC speed assignment. Here, it means the speed recommendation comes from a ground system; if ATC issues it as an instruction, respond and comply as you normally would.
Example Sentence 1
Center issued a GIM-S speed advisory of 270 knots to maintain spacing behind the arrival ahead.
Example Sentence 2
After accepting the ground-based interval management spacing speed advisory, the crew reduced thrust slightly and stayed on the published arrival route.