Spatial Disorientation Event During Flight Due to Proposed Reverse-Dip Visual Illusion

Spatial disorientation is a leading nontechnical cause of fatal military aviation accidents, triggered by insufficient or misleading cues mainly from the visual and vestibular systems. Spatial disorientation accounts for 20-38% of fatal military aviation accidents, but case reports describing specific illusions during actual flight are rare.

On a clear night, an aerial refueling tanker was cruising at 16,000 ft (4877 m), while an F-15I fighter aircraft was 3 mi behind and 971 ft (296 m) below. About 100 s before a near collision, the fighter pilot switched to Air-to-Air mode, displaying the distance and speed difference to the tanker via a Target Designator box on the Head-Up Display. However, the crew did not realize they were accelerating toward the tanker [from 597-663 ft · s-1 (182-202 m · s-1)] or climbing by 738 ft (225 m). The two aircraft came within 49 ft (15 m) of each other before the navigator noticed the tanker and initiated a roll to the left.

The dip illusion occurs when a pilot flying in trail attempts to maintain the image of the lead aircraft in a fixed position on the windscreen as separation increases, which can lead to unintentional descent. In this case, we propose a "reverse-dip" illusion. The fighter crew was unaware they were closing in on the tanker, causing the Target Designator box to rise in the Head-Up Display. The pilot instinctively pulled back on the stick to maintain the box's position, resulting in an unintentional climb. Recognizing how such illusions develop in flight is essential to reducing future risks. Nakdimon I, Gordon B. Spatial disorientation event during flight due to proposed reverse-dip visual illusion. Aerosp Med Hum Perform. 2025; 96(11):1015-1018.