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’s symptoms are consistent with hyperventilation — breathing faster or deeper than required, which lowers the blood’s carbon dioxide (CO₂) level. Typical signs include dizziness, tingling around the mouth or in the fingers, chest discomfort, visual disturbance and anxiety.

ATPL theoretical-knowledge context

For an EASA ATPL examination, Subject 040 learning objective 37 lists the following measures to counteract hyperventilation: slow the breathing, close one nostril, speak aloud, or place a paper bag over the nose and mouth. Therefore, where a multiple-choice question specifically tests the EASA ATPL syllabus, the paper-bag answer may be the expected theoretical response.

Operational context

In an actual passenger event, these symptoms are not diagnostic of hyperventilation and may also occur with hypoxia or a cardiac, respiratory or neurological problem. Inform the cabin crew, reassure the passenger, encourage slow and controlled breathing, monitor the passenger, and obtain medical assistance as required. Do not substitute an examination mnemonic for the applicable onboard procedure.

Safety note: This answer explains ATPL theoretical knowledge and is not medical advice. Always follow the operator’s Operations Manual, company procedures and the instructions of qualified cabin crew or medical personnel. Current first-aid guidance may advise against paper-bag rebreathing because it can worsen an incorrectly diagnosed condition.

References: EASA Subject 040, learning objective 37; St John Ambulance — hyperventilation first-aid guidance.

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.