Definition
The collection of physiological and environmental conditions that reduce a pilot's ability to see clearly, especially at night. Common factors include lack of oxygen (hypoxia) at higher altitudes, exposure to carbon monoxide from cabin heaters or exhaust leaks, fatigue, dehydration, smoking, certain medications, low cabin lighting, dirty or scratched windscreens, glare from cockpit lights or outside sources, and the natural decline of visual acuity with age.
Plain English
The things that make it harder for a pilot to see well, particularly in the dark. Some come from inside the body (tiredness, low oxygen, illness) and some come from outside (cockpit glare, a dirty windscreen, weather).
Context Anchor
Seen in night flying training, preflight planning, and personal fitness checks before a flight.
Derivation
Factor comes from a Latin word meaning “to make or do.” A factor is something that helps make a result happen. Vision comes from a Latin word meaning “to see.” Together, the phrase means the things that help determine how well you can see.
Why Pilots Care
These factors can sharply reduce night vision effectiveness, increasing the chance of disorientation or missed visual cues during flight.
Grounding Statement
Your eyes may be healthy, but conditions around you and inside your body can still make them perform below normal.
Intuition Check
Do not read this as only “bad eyesight.” In this context, it also includes temporary conditions, such as fatigue, altitude, smoke, alcohol, or bright light, that can reduce normal vision.
Example Sentence 1
During his night flight briefing, the instructor reviewed the factors affecting vision and recommended using supplemental oxygen above 5,000 feet.
Example Sentence 2
Avoiding alcohol the day before flying helps minimize one of the common factors affecting vision at night.