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AI.II.B.K2FAA-S-ACS-25 · Nov 2023Knowledge

Vestibular and visual illusions.

ACS element text (the applicant demonstrates understanding of)

Vestibular and visual illusions.

Bottom line

When visual contact with the horizon is lost, the vestibular system becomes unreliable. Spatial disorientation from these illusions can be prevented only by visual reference to reliable, fixed points on the ground or to flight instruments.

FAA references

  1. AIM 8-1-5 (Illusions in Flight) — AIM Basic 2/20/25 w/ Change 1 (8/7/25) & Change 2 (1/22/26)
  2. PHAK ch. 17 (p. 17-6) — FAA-H-8083-25C (2023)
  3. AFH ch. 5, Human Factors (p. 5-3) — FAA-H-8083-3C
  4. AFH ch. 18 (p. 18-18) — FAA-H-8083-3C
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