Human Performance

Circadian rhythm is the body’s internal biological clock, regulating sleep-wake cycles over approximately 24 hours. During long-haul operations that cross multiple time zones, pilots may be required to operate during the circadian low—typically between 2 a.m. and 6 a.m. body time—when alertness, cognitive performance, and reaction time are at their lowest. This misalignment can lead to increased fatigue, reduced situational awareness, and a higher risk of errors.

The passenger is likely experiencing hyperventilation.

Hyperventilation occurs when a person breathes too rapidly or too deeply, leading to a decrease in carbon dioxide (CO₂) levels in the blood. This can result in symptoms such as:
- Dizziness
- Tingling or numbness
- Chest discomfort
- Shortness of breath
- Visual disturbances
- Anxiety or panic

How to manage hyperventilation:

• Reassure the passenger and encourage calm, slow breathing.
• Have them breathe into a paper bag or cupped hands to help restore CO₂ levels (if no other medical contraindications are suspected).
• Remove sources of stress and provide a calm environment.
• If symptoms persist or worsen, seek medical assistance as needed.

Note: It is important to differentiate hyperventilation from other medical conditions (e.g. hypoxia or cardiac issues), so careful observation and judgment are required.

A wider-than-usual runway, such as one 60 metres wide, can create the illusion that the aircraft is lower than it actually is, potentially leading to a higher-than-normal approach path.

The visual black hole effect is a hazardous illusion encountered during night approaches over featureless terrain (e.g. sea, desert, unlit terrain), where there are no peripheral visual cues between the aircraft and the runway.

What causes the illusion?

Pilots affected by this illusion tend to unconsciously fly a curved, low approach path, instead of maintaining a safe, constant-angle glidepath.

According to Kraft and Elworth's theory, this happens because the pilot tries to keep the visual angle to the runway constant (i.e. the angle between the eye and the runway appears unchanging).
This null angular change creates the illusion of a stable approach, but in reality, the aircraft is descending below the correct glidepath, increasing the risk of controlled flight into terrain (CFIT).

In the illustration, both the safe path and the curved path create the same visual angle (Θ), giving the false perception of being on the right glide.

How to prevent it:

• Avoid relying solely on visual cues, especially at night.
• Use instruments, ILS, or PAPI/VASI to monitor the correct glidepath.
• Follow stabilised approach procedures and cross-check descent rates and altitudes.

This illusion shows how the human visual system can be misled, especially in poor visual environments.