NCAA Namibia Night Rating Theory key terms

Vision used in very dim light, provided by rod cells. It is poor at resolving detail and colour but is most sensitive to faint light and to movement off to the side of the gaze.

Daylight vision provided by cone cells, giving sharp detail and full colour. It needs relatively bright light, so it fades quickly after sunset and cannot be relied on in a dark cockpit.

The transitional vision state at dusk and dawn, when both rods and cones contribute. Acuity and colour judgement are unreliable, and depth perception and judging distance are especially poor during this period.

Light-sensitive retinal cells that work in dim light. They contain rhodopsin, are absent from the central fovea, and are densest about 15 to 20 degrees off centre, which is why faint objects are seen better by looking slightly to one side.

Retinal cells responsible for colour and fine detail. They are concentrated in the fovea and need good light, so colour-coded information such as chart or instrument colours becomes hard to distinguish at night.

The light-sensitive pigment in rod cells. It is bleached by bright light and takes roughly 20 to 30 minutes to regenerate, which is the basis of the dark-adaptation period before night flight.

The gradual increase in eye sensitivity after exposure to bright light, taking about 20 to 30 minutes for useful night vision. It is destroyed quickly by a single bright flash, so cockpit white light and torches must be used sparingly.

A technique of looking about 10 to 15 degrees to one side of a faint object so its image falls on the rod-rich part of the retina. It improves detection of dim lights but reduces the ability to judge shape and detail.

A tendency for the eye to focus at roughly one metre when looking into a dark, featureless sky. Distant aircraft or lights may then appear blurred or be missed until the pilot deliberately focuses on a distant reference.

An illusion in which a single stationary light viewed against a dark background appears to drift or move. It is countered by fixing the gaze on a steady reference and by cross-checking instruments.

A night approach over unlit terrain with few ground cues, where the pilot tends to fly too low and steeply. It is countered by using the approach slope indicator, the altimeter and a stabilised approach profile.

A misleading visual reference, such as a sloping cloud bank or a line of shore lights, that the pilot mistakes for the true horizon. It can lead to an unintended bank or pitch attitude unless instruments are cross-checked.

A false sensation of pitch caused by acceleration or deceleration, which the body interprets as a climb or descent. On a night go-around or initial climb it can provoke an incorrect nose-down or nose-up input.

A false attitude sensation arising from body pressure cues rather than the inner ear, for example feeling pushed back into the seat during acceleration and reading it as a nose-up attitude.

The inner-ear organs that sense rotation and acceleration. They cannot reliably distinguish sustained turns or small accelerations from straight flight, so they can produce convincing but false sensations at night without visual reference.

A false sensation of banking after a turn is rolled out smoothly, caused by the inner ear adapting to the turn. The pilot feels tilted and may lean the aircraft into a real bank unless instruments are trusted.

Cockpit illumination in red or filtered light chosen because it preserves rod dark adaptation better than white light. Excessive brightness still degrades night vision, so intensity should be set to the minimum usable level.

Image-intensifying headgear that amplifies available light for low-level night operations. They narrow the field of view, reduce colour and depth cues, and require training in their limitations and in the effect of bright light sources.

Insufficient oxygen reaching body tissues. At night even mild hypoxia causes a measurable loss of night vision and judgement before other symptoms appear, so oxygen use and cabin altitude need careful management.

A state of reduced alertness and performance caused by prolonged wakefulness, workload or disrupted rest. At night it slows reactions, increases errors and raises the risk of unintentional sleep, so flight-time limits and rest planning matter.

The body's roughly 24-hour cycle that governs alertness and sleepiness. It produces a natural low point in the early hours of the morning, when night duty carries the highest risk of drowsiness and degraded performance.

A short, planned period of rest on the flight deck during low-workload cruise, used with company approval to counter fatigue. It must be brief enough to avoid sleep inertia and must not reduce the required crew alertness.

The temporary grogginess and slowed performance after waking, which can last several minutes. It is why a crew member should not be woken and immediately expected to handle an abnormal or emergency situation.

A failure to correctly perceive the aircraft's attitude or motion relative to the earth, usually from conflicting or absent visual cues. It is a major night and instrument-flying hazard and is resolved by relying on instruments.

A disciplined, continuous scan of the flight instruments used to confirm attitude, altitude and heading. At night it is the primary defence against visual illusions and spatial disorientation, even in visual conditions.

A rotating or flashing light at an aerodrome that identifies its position from a distance at night. Its colour and flashing pattern are published, and it helps the pilot locate the field before identifying the runway lights.

A sequence of lights leading to the runway threshold that provides roll and alignment guidance in poor visibility or darkness. Its length and configuration are published, and it helps the pilot judge distance and alignment on final.

A ground light system, such as PAPI or VASI, that shows whether the aircraft is on, above or below the correct approach slope. It is a key defence against a too-low night approach over unlit terrain.

Lights along the sides of a runway marking its width and extent at night. Their colour and spacing are standardised, and they help the pilot judge runway alignment and the point of touchdown.

Lights marking the beginning of the usable landing surface, normally green facing the approach. They confirm the touchdown zone and help the pilot judge height and distance on short final at night.

A system allowing the pilot to switch on or increase aerodrome lighting by radio, often by keying the microphone a set number of times. It is essential at unattended aerodromes and the correct procedure must be known before departure.

The recency requirement that a pilot must meet before carrying passengers at night, typically involving a set number of night take-offs and landings within a defined period. It is a legal prerequisite, not merely good practice.

An authorisation added to a pilot licence permitting flight at night under the applicable rules. It requires specific ground and flight training, including instrument flying, and is issued by the national aviation authority.

The set of operating rules for visual flight at night, covering required equipment, lighting, visibility minima and, in many states, a minimum height above terrain. Pilots must know the specific national requirements before planning a night flight.

A routine or special observation issued for an aerodrome, giving wind, visibility, weather, cloud and temperature. At night, cloud base and visibility trends are critical because ground references are already limited.

A coded forecast of conditions expected at an aerodrome over a stated period, including temporary and probability variations. Night planning depends on comparing the forecast with the actual report and the trend.

The height of the lowest cloud layer reported as broken or overcast, or of the vertical visibility into obscuration. A low night ceiling removes the horizon and increases the risk of spatial disorientation.

A confirmed aircraft position derived from navigation aids, radio aids or visual references. At night, fewer ground features are visible, so fixes should be taken more frequently and cross-checked against dead reckoning.

Calculating position from the last known fix using heading, speed, time and wind. At night it is the fallback when visual fixes are unavailable, so accurate logs and regular timing are essential.