CA.I.C.K3aFAA-S-ACS-7B · Nov 2023Knowledge

a. Atmospheric composition and stability

ACS element text (the applicant demonstrates understanding of)

Meteorology applicable to the departure, en route, alternate, and destination under visual flight rules (VFR) in Visual Meteorological Conditions (VMC), including expected climate and hazardous conditions such as: a. Atmospheric composition and stability

Bottom line

VMC means visibility, distance from cloud, and ceiling meet or exceed the minimums specified for VFR. Prior to every flight, pilots should gather all information vital to the nature of the flight, including a weather briefing obtained using online weather resources, a dispatcher, or Flight Service. Continued VFR flight from VMC into marginal VMC and IMC is a factor contributing to loss of control in-flight (LOC-I).

Key numbers

Key numbers for a. Atmospheric composition and stability
NumberWhat it means
15 to 20 minutes old by the time data sets are assembled and displayed in a cockpitNEXRAD age
6 hours or more before departureOutlook window
significant changes expected within 1 hour before and after the ETADestination forecast

FAA references

  1. PHAK Glossary (p. G-33) — FAA-H-8083-25C (2023)
  2. AWH ch. 3 (p. 3-3) — FAA-H-8083-28A
  3. AFH ch. 5, Human Factors (p. 5-2) — FAA-H-8083-3C
  4. AC 91-92, paras. 7.6, 7.7 — AC No: 91-92
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