AIM ¶ 4-2-11 — Speed Phraseology
AIM 4-2-11: How pilots and ATC say airspeeds and Mach numbers on the radio. Examples, phraseology rules, and oral exam prep for student pilots.
In Plain English
AIM 4-2-11 explains how to say airspeeds and Mach numbers correctly on the radio. Clear, standardized phraseology prevents misunderstanding between pilots and controllers — especially during speed adjustments in busy airspace.
Knots:
- Speak each digit separately, followed by the word "KNOTS."
- Examples: 250 → "two five zero knots"; 190 → "one niner zero knots."
- Controllers may omit "KNOTS" when issuing speed adjustments, e.g., "REDUCE SPEED TO TWO FIVE ZERO."
Mach Number:
- Precede the digits with the word "Mach" and speak each digit individually.
- Examples: 1.5 → "Mach one point five"; 0.64 → "Mach point six four"; 0.7 → "Mach point seven."
Why it matters: using standard phraseology keeps frequencies efficient and reduces readback errors. Even though AIM is non-regulatory, controllers expect this format, and using it cleanly on your checkride demonstrates professional radio discipline.
AIM Source Text
FAA AIM ¶ 4-2-114-2-11. 4-2-11. Speeds
The separate digits of the speed followed by the word “KNOTS.” Except, controllers may omit the word “KNOTS” when using speed adjustment procedures; e.g., “REDUCE/INCREASE SPEED TO TWO FIVE ZERO.” EXAMPLE- (Speed) 250 two five zero knots (Speed) 190 one niner zero knots The separate digits of the Mach Number preceded by “Mach.” EXAMPLE- (Mach number) 1.5 Mach one point five (Mach number) 0.64 Mach point six four (Mach number) 0.7 Mach point seven
Oral Exam Questions a DPE Might Ask
Q1How do you read back an airspeed of 250 knots per the AIM?
Per AIM 4-2-11, state the separate digits followed by the word "KNOTS" — "two five zero knots."
Q2When may a controller omit the word "KNOTS" in a transmission?
Per AIM 4-2-11, controllers may omit "KNOTS" when using speed adjustment procedures, e.g., "REDUCE/INCREASE SPEED TO TWO FIVE ZERO."
Q3How is a Mach number such as 0.64 spoken on the radio?
Per AIM 4-2-11, precede the separate digits with "Mach" — 0.64 is spoken as "Mach point six four."
Related Paragraphs in AIM Chapter 4