Definition
An air traffic control notation indicating that greater-than-standard separation must be applied between aircraft due to specific operational conditions, such as wake turbulence, equipment limitations, or special procedures in effect.
Plain English
A note used by controllers meaning aircraft must be kept further apart than usual because something about the situation calls for extra spacing.
Context Anchor
Seen in air traffic control and FAA glossary material when discussing required spacing between aircraft.
Why Pilots Care
The instruction protects against wake turbulence encounters or other hazards that standard spacing would not cover.
Analogy
It is like leaving extra distance behind a large truck on a road because the air and spray behind it can disturb what follows. The larger or more disruptive the vehicle ahead, the more space you may need.
Intuition Check
Do not read “increased separation required” as a suggestion or a general caution. In this FAA use, it means the required spacing between aircraft is greater than normal.
Example Sentence 1
The controller noted ISR was in effect behind the heavy jet and extended our final approach spacing accordingly.
Example Sentence 2
Due to the thunderstorm outflow, ISR was applied between successive arrivals on the same runway.