Definition
Air traffic control instructions directing a pilot to fly at a specified indicated airspeed, or to increase or reduce the current airspeed by a specified amount, in order to achieve or maintain required separation between aircraft, sequence aircraft into a traffic flow, or manage arrival spacing. Pilots are expected to comply promptly and to advise ATC if the assigned speed cannot be maintained. The controller must be informed any time the speed varies by more than 10 knots or 0.02 Mach from the assigned value.
Plain English
When a controller tells you to fly faster or slower, or to hold a specific airspeed, so they can space your aircraft properly with others. You either do it, or you tell them you can't.
Context Anchor
You may hear speed adjustments from air traffic control during arrivals, approaches, or radar vectors, especially when several aircraft are being sequenced into the same airport.
Why Pilots Care
Following these instructions prevents traffic conflicts and keeps the arrival sequence orderly and safe.
Intuition Check
Do not read “adjustment” as a casual or optional tweak. In this context, a speed adjustment is a specific speed change used to manage traffic or meet a procedure, but it never overrides safe aircraft control.
Example Sentence 1
Approach issued a speed adjustment of 'reduce speed to 210 knots' to space us behind the regional jet on final.
Example Sentence 2
After receiving the speed adjustment to 170 knots, the pilot reduced power and configured the aircraft for landing.