Visual Scanning and Collision Avoidance

A series of short, regularly spaced eye movements that bring successive areas of the sky into the central visual field. Each movement should not exceed 10°, and each area should be observed for at least 1 second to enable detection (PHAK ch. 14).

Most pilots prefer back-and-forth eye movements, but each pilot should develop a comfortable pattern and then adhere to it. Even when entitled to the right-of-way, yield if another aircraft seems too close.

Because the eye only resolves detail in the small central field served by the cones, and it cannot resolve a target while moving. The scan works by stopping: each stop parks a new 10° block of sky on the fovea long enough — a second — for detection to happen (PHAK ch. 14). A continuous sweep never stops, so nothing is ever imaged on the part of the retina capable of seeing it.

That is the physiological answer to the student who says "I was looking outside the whole time."

• Reduced scan frequency from concentrating on flight instruments or tablets, and distraction with passengers
• Blind spots from high-wing and low-wing geometry, windshield posts, and sun visors
• Prevailing weather conditions, including reduced visibility and the position of the sun
• Aircraft attitude, which creates additional blind spots
• Physical limitations of the eye — time required to refocus between near and far objects, empty-field myopia, and narrow field of vision

Empty-field myopia: with nothing to focus on — a hazy or featureless sky — the eye relaxes to an intermediate focal distance of a few feet and effectively sees nothing beyond it.

Defense: the disciplined stop-and-look scan — give the eye a real object to focus on in each block. Where possible, focus on a distant object (a cloud edge, a ridgeline, a wingtip) to reset focus before resuming the scan (PHAK ch. 14 lists empty-field myopia among the physical limitations of the eye).

The optic disk, where the optic nerve meets the retina, has a total absence of rods and cones — each eye is completely blind there. Under normal binocular vision it is not a problem because an object cannot be in the blind spot of both eyes at once. But if one eye's field is obstructed — by a windshield divider or another aircraft — a target can fall in the other eye's blind spot and go completely undetected (PHAK ch. 17).

At night there is an additional problem: under scotopic vision a night blind spot appears in the central field of view as cone sensitivity is lost (PHAK ch. 17).

• Before takeoff — before taxiing onto the runway, scan the approach area for landing traffic, maneuvering as needed to get a clear view of the approach areas
• Climbs and descents — execute gentle banks left and right at a frequency that permits continuous scanning
• Straight and level — appropriate clearing procedures at periodic intervals
• Traffic patterns — avoid entries while descending
• Traffic at VOR sites — sustained vigilance because of converging traffic at VORs and intersections
• Training operations — clearing turns before every practice maneuver, and have the student verbalize the clearing ("clear left, right, above, and below")

• High wing — momentarily raise the wing in the direction of the intended turn and look
• Low wing — momentarily lower the wing in the direction of the intended turn and look

(PHAK ch. 14.) Then teach the same discipline for the door post, the sun visor, and the panel glare shield: move your head, not just your eyes.

Appropriate clearing procedures should precede the execution of all turns, including chandelles, lazy eights, stalls, slow flight, climbs, straight and level, spins, and other combination maneuvers (PHAK ch. 14). The list is deliberately broad — "we're just doing slow flight" is not an exception.

An aircraft on a collision course shows no apparent relative motion — it sits in the same spot on your windshield and grows. Because there is no movement to trigger peripheral detection, the target that is actually going to hit you is the hardest one to see, which is precisely why the stop-and-look scan exists (PHAK ch. 14 on relative motion and scanning technique).

Teach the corollary: traffic that is moving across your windshield will pass in front of or behind you; traffic that is stationary and getting bigger requires action now.

12.5 seconds from first seeing the object to the airplane beginning to move (AC 90-48E, Table 1):

Note where the time goes: 9 of the 12.5 seconds are cognitive — realizing it is a threat and deciding what to do. Add the 1 to 2 seconds the eye needs to refocus from the panel to a target a mile away (AC 90-48E 8.1.4), and a head-down glance is genuinely expensive.

Turn it into arithmetic on the whiteboard. Two trainers converging head-on at 120 knots each close at 240 knots — about 405 feet per second. Multiply by the 12.5-second budget from AC 90-48E: you need roughly 5,000 feet, about 0.8 NM, of separation at the moment you first see the target just to begin maneuvering. Against a 250-knot jet below 10,000 feet the number gets much worse.

Then make the teaching point that the student will remember: at those closure rates you are not "avoiding traffic," you are spending a budget you were issued the instant it became visible. That reframes the scan from a habit into a countermeasure — and it is the argument for the mitigations in this Task: standard pattern entries, altitude selection, position reports, and ADS-B In folded into the scan rather than replacing it.

ADS-B In is an effective aid to see and avoid. Incorporate the traffic display into the normal traffic scan rather than treating it as a separate task, and understand the unit's visual and audio alerting features — systems with traffic alerting help minimize the tendency to fixate on the display. Before taxiing onto a movement area, ADS-B In can give advance indication of arriving aircraft and traffic in the pattern (PHAK ch. 14).

The limitation you must teach: in certain airspace not all aircraft are equipped with ADS-B Out or transponders, so they will not appear on your display at all (PHAK ch. 14). A clean screen is not a clear sky.

• Use ADS-B In properly and understand its limitations
• Limit the amount of time you focus on flight instruments or tablets
• Develop a strategic approach to scanning — scan the entire sky and try not to focus straight ahead

For an instructor, that middle bullet is a self-critique tool: count how much of the lesson you spent looking at the student's altimeter.

The integrated flight instruction standard is that approximately 90 percent of the pilot's attention should be devoted to outside visual references and scanning for airborne traffic, with the instruments used to validate attitude and confirm performance (AFH ch. 3). As the instructor you are the safety pilot for a person who is, by definition, saturated — so the split is asymmetric. The student's scan will collapse inward the moment the task gets hard; yours has to expand to cover it.

Practical technique: narrate your own scan out loud during demonstrations, and require the student to verbalize clearing (PHAK ch. 14). Verbalizing is not ceremony — it is how you audit whether the scan actually happened.

• Instruction itself. Explaining a concept pulls both people's eyes inside. Brief on the ground, not at 2,500 feet.
• The tablet. PHAK ch. 14 names concentration on flight instruments or tablets as the first listed limitation on scan frequency.
• The radio. A busy frequency during a pattern entry is where students stop looking.
• The student's error. Fixating on a 200-foot altitude deviation while an airplane converges is the classic instructor trap.

The mitigation is task management: decide in advance what you will let slide. Altitude tolerance is negotiable; the scan is not.

Because traffic density concentrates where everyone converges: the vicinity of an airport — PHAK ch. 14 says scanning is "particularly important in the vicinity of an airport" — and at VORs and intersections, where sustained vigilance is required due to converging traffic. Add training operations to the list; the practice area near a busy flight school is a high-density environment full of airplanes flown by people whose scans are still developing.

Mitigations to teach: standard pattern entries (never descending into a pattern), position reporting at nontowered fields, flight following where available, and choosing practice altitudes and areas deliberately rather than habitually.

• Photopic — high light, central viewing, good color, cones, acuity 20/20, blind spot present by day
• Mesopic — medium/low light, both receptor types, some color, acuity varies — considered the most dangerous period for viewing
• Scotopic — low light, scanning technique required, no color perception, rods only, acuity 20/200 or less

(PHAK ch. 17.) As cone sensitivity decreases in mesopic conditions — dawn, dusk, full moonlight — the pilot must switch to off-center vision and proper scanning technique to detect objects.

View the object by looking 10° above, below, or to either side of it so peripheral (rod) vision maintains contact. The trap: an image viewed off-center for longer than 2 to 3 seconds will disappear, because the rods reach a photochemical equilibrium that prevents further response until the scene changes (PHAK ch. 17). So off-center viewing must keep moving — look slightly away, then shift again.

Dark adaptation background: cones adapt rapidly, but the rods take approximately 30 minutes to fully adapt, and a single bright light can completely destroy that adaptation (PHAK ch. 17).

The visual system dominates and is the reliable one; the vestibular and somatosensory systems mislead when outside references are lost. Teach it as an ordering rule: outside horizon first, instruments to validate, and never the seat of the pants. The specific illusions — the leans, Coriolis, graveyard spiral, somatogravic, false horizon, autokinesis — are covered under Task II.A and Task II.M; here the teaching angle is that a scan that has quietly gone inside is also a scan that has stopped cross-checking the horizon, which is how a VFR pilot ends up disoriented in deteriorating conditions.

Simulated instrument flight requires a safety pilot occupying the other control seat with adequate vision forward and to each side, and the airplane must be equipped with fully functioning dual controls (91.109). The safety pilot's name must be recorded in the logbook entry for the flight (61.51(b)(1)(v)).

The instructional point: a hooded student sees nothing, so 100 percent of the see-and-avoid burden shifts to one person whose own scan is degraded by the workload of monitoring the student. Brief before the hood goes on: who clears for which turns, what the terminating phrase is, and the positive three-step exchange of controls (AIH ch. 9).

14 CFR part 91 establishes right-of-way rules, minimum safe altitudes, and VFR cruising altitudes to enhance flight safety, and the pilot contributes to collision avoidance by being alert and scanning for other aircraft (PHAK ch. 14). Vigilance to see and avoid other aircraft applies regardless of whether the operation is conducted under IFR or VFR, and regardless of ATC services — flight following is an aid, not a transfer of responsibility.

Teach the right-of-way rules alongside the scan (91.113), and teach the yield-anyway rule from PHAK ch. 14: even when entitled to the right-of-way, give way if another aircraft seems too close.