Definition
An ATC phrase used in speed adjustment instructions, indicating the indicated airspeed (in knots) that the pilot is expected to fly and hold. When ATC issues a speed and uses this phrase, the pilot is required to maintain that speed within plus or minus 10 knots, or in the case of helicopters within plus or minus 5 knots, until further advised.
Plain English
When a controller tells you a number of knots to fly, this is the speed they want you to hold steady — not a target to drift around, but a speed to lock onto and keep until they say otherwise.
Context Anchor
Used when reading or hearing speed instructions, especially ATC instructions such as “maintain 170 knots.”
Derivation
Maintain comes from older words meaning “to hold” or “to keep.” That helps here because the instruction is about holding a speed steadily, not merely touching that speed for a moment.
Why Pilots Care
Ensures proper spacing, sequencing, and separation from other aircraft; deviating without clearance can compromise safety or traffic flow.
Intuition Check
Do not read “the speed to be maintained” as a target you may pass through briefly. In this context, it means the speed you are expected to hold until something changes it.
Example Sentence 1
ATC instructed, "Maintain 250 knots," and the crew adjusted thrust to hold that speed within the required tolerance.
Example Sentence 2
Approach assigned the speed to be maintained of 180 knots to keep proper spacing behind the aircraft ahead.