Visual scanning is the systematic observation of airspace for traffic detection — the most effective method against mid-air collisions.
Why scan?
- The eye sees sharply only in the fovea (~2° field) — the size of a thumbnail at arm's length.
- Peripheral vision detects motion but little detail.
- Stationary objects (traffic on collision course appears stationary — "Constant Bearing, Decreasing Range") are especially hard to see — active eye movement required.
The "block" method (aviation standard)
- Divide the field into segments of about 10° each.
- Per segment, focus 1–2 seconds (the time the eye needs to actually fix on the area).
- Eyes still on the segment, do not sweep continuously.
- After 1–2 s move to the next segment.
- Cover the horizontal 60° to each side of the nose systematically.
Night scanning
At night off-centre vision is mandatory (see §5.1):
- Look ~ 10–15° off the suspect object, not directly.
- Move the eyes — a stationary rod patch "shuts off".
Constant Bearing, Decreasing Range
Two aircraft on collision course have a constant relative bearing — the other aircraft stays in the same cockpit-window position, only growing larger. Very hard to detect!
→ If traffic does not move in the cockpit window: raise awareness and prepare to manoeuvre.
Sources of distraction
- In-cockpit activities (charts, GPS, radio) — minimise in critical phases
- Sun glare — use sunglasses (see "Eye protection")
- Sterile cockpit at take-off and approach