Which illusion was likely affecting the first officer on Atlas Air 3591?

• A. Vestibular illusion
• B. Visual illusion due to sun glare
• C. Somatogravic illusion
• D. False horizon illusion

Answer: (C)

Somatogravic illusion is a vestibular effect caused by linear acceleration or deceleration. When the aircraft is speeding up or slowing down, the inner ear’s otolith organs can signal a change in pitch even if the airplane’s actual attitude hasn’t changed, leading a pilot to misread the true pitch and, consequently, the flight path.

On this approach, the airplane was decelerating as it descended toward the airport. That deceleration can trigger a somatogravic illusion, making the first officer feel as though the nose is in a different attitude than it truly is. If visual cues are limited or ambiguous, reliance on this misleading perception can cause inaccurate pitch control and a descent profile that isn’t aligned with the instrument indications and the required approach path. This combination of misperceived attitude and degraded visual references is why somatogravic illusion is identified as the likely factor in this scenario.

Visual glare or misreading a false horizon require different conditions and cues, so they’re less consistent with the circumstances described for this incident.