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IR.I.B.K3lFAA-S-ACS-8C · Nov 2023Knowledge

l. Obstructions to visibility (e.g., smoke, haze, volcanic ash, etc.)

ACS element text (the applicant demonstrates understanding of)

Meteorology applicable to the departure, en route, alternate, and destination for flights conducted under Instrument Flight Rules (IFR) to include expected climate and hazardous conditions such as: l. Obstructions to visibility (e.g., smoke, haze, volcanic ash, etc.)

Bottom line

PIREPs are a valuable source of in-flight information regarding en route conditions including turbulence, icing, visibility, temperature, and winds aloft.

Key numbers

Key numbers for l. Obstructions to visibility (e.g., smoke, haze, volcanic ash, etc.)
NumberWhat it means
4 hours (6 hours if the SIGMET relates to a hurricane)SIGMET valid
visibilities below three milesDust storm SIGMET
first 12 hours of the forecast periodHigh-level SIGWX
15 to 20 minutes old when displayed in a cockpitNEXRAD age

FAA references

  1. PHAK ch. 13 (p. 13-12) — FAA-H-8083-25C (2023)
  2. PHAK ch. 13 (p. 13-7) — FAA-H-8083-25C (2023)
  3. AWH ch. 3 (p. 3-25) — FAA-H-8083-28A
  4. AC 91-92, paras. 4.17, 7.6, 7.7 — AC No: 91-92
  5. RMH ch. 3 (p. 3-8) — FAA-H-8083-2A
  6. AFH ch. 7 (p. 7-1) — FAA-H-8083-3C
  7. PHAK ch. 12 (p. 12-20) — FAA-H-8083-25C (2023)
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