In reviewing Academy exam questions, it was discovered that a question regarding calm wind in the Basic ATC/S1 Exam was misleading and ambiguous. It has since been corrected.

Part of the misconception over the question and its answer stems from a rather confusing and incongruous definition of calm wind. To help, consider memorizing a specific order to the words: wind calm vs calm wind.

Think of this! In conversation, you would not say, "it feels as though the wind calm." The absence of "is" makes the sentence incomplete. "Wind Calm" is not meant to be conversational, and that's because it's meant to be ATC phraseology. For this reason, how we define wind as being calm in relation to ATC and describing it to pilots over frequency can be answered by looking in the Air Traffic Control Handbook (7110.65).

Follow me so far? Great! "Wind Calm" as referenced in 7110.65, 2-6-3 is as follows:

Quote

b. Describe the wind as calm when the wind velocity is less than three knots.

Awesome! So, where does the confusion set in? 

"Calm wind" has a different definition depending upon the resource in which you find the reference.

• In the Aeronautical Information Manual (AIM) Chapter 7, Section 1: Meteorology, you'll find mention of calm wind being described in a Terminal Area Forecast (TAF) as a velocity of 3 knots or less.
• And, in JO 7900.5 Surface Weather Observing, 7.8, you'll find mention of calm wind as being described as a velocity of less than 1 knot by a qualified weather observer in accordance with the Beaufort scale.

While they exist and might be pertinent in a variety of aviation applications, neither of these two listed resources directly impact or influence the job of the air traffic controller in relation to their ATC duties in the handling of air traffic. As it pertains to the safe operation of air traffic, ATC needs only to refer to the 7110.65 (mentioned at the beginning of this post) when describing wind as calm to aircraft.

To help differentiate and segregate all of the aforementioned resources, think of the specific word order: calm wind vs wind calm. Then, make sure you understand the context in which the words are mentioned.

• Am I being asked to describe the definition of wind calm? If YES, then "less than 3 knots" (7110.65)
• Is this in reference to ATC phraseology or job duty? If YES, then "less than 3 knots" (7110.65)
• Am I being asked to define the definition of calm wind as it relates to forecasting? If YES, then "3 knots or less" (AIM)
• Am I being asked to define the definition of calm wind as a trained observer? If YES, then "less than 1 knot" (7900.5)

Hopefully this helps to clear up some of the confusion regarding calm wind vs wind calm!   

NOTE: This tutorial does not intend on exploring the difference between "Wind Calm" and "Calm Wind Runway." For more information about "Calm Wind Runway" as it pertains to ATC, please review 7110.65, 3-5-1.