U.S.Department
of Transportati
Federal Aviation
Ministration
Advisory
Circular
Subject: ATMOSPHERIC TURBULENCE
Date: 9/9/97
AC No: 00-30B
AVOIDANCE
Initiated By: AFS-400
Change:
1. PURPOSE. This Advisory Circular (AC) describes to pilots, aircrew members,
dispatchers, and other operations personnel the various types of clear air turbulence
(CAT) and some of the weather patterns associated with it. Also included are “Rules of
Thumb” for avoiding or minimizing CAT encounters. Appendix 1provides a sample
Atmospheric Hazards Advisory and Avoidance System that air carriers can tailor to
their specific needs.
2. CANCELLATION. AC 00-30A, Rules of Thumb for Avoiding or Minimizing
Encounters With Clear Air Turbulence, dated November 21, 1988, is cancelled.
3. RELATED READING MATERIAL.
a. AC 00-6A, Aviation Weather.
b. AC 00-45, Aviation Weather Services (current edition).
c. AC 61-23, Pilot’s Handbook of Aeronautical Knowledge (current edition).
4. BACKGROUND.
a. In 1966, a National Committee for Clear Air Turbulence officially defined CAT as
“all turbulence in the free atmosphere of interest in aerospace operations that is not in or
adjacent to visible convective activity (this includes turbulence found in cirrus clouds not in
or adjacent to visible convective activity).” Overtime, less formal definitions of CAT have
evolved. The Aeronautical Information Manual expands the basic CAT definition as
“turbulence encountered in air where no clouds are present.” This term is
commonly
applied to higher altitude turbulence associated with windshear. Thus, clear air turbulence
or CAT has been defined in several ways, but the most comprehensive definition is:
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