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Visual Scanning & Collision Avoidance

Introduction:

  • According to NTSB statistics, mid-air collisions are likely to happen:
    • VFR, daylight, weekend
    • Below 3,000' AGL at uncontrolled airport within 10nm, 8,000' AGL within 25nm
    • Great weather
    • All pilot skill levels
    • Pleasure flight, no flight plan
    • Within 5 miles of towered and 10 miles of non-tower airports
    • Transition to/from the traffic pattern (crossing or overtaking maneuvers)
    • Primarily in the traffic pattern
  • Constantly checking for traffic should be a habit - a way of life
  • The pilots vision and techniques to scan for other aircraft are paramount
    • FAR 91.113(b) "See and Avoid" ...Vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft
      • This also includes IFR flights when in VMC

Situational Awareness:

  • Situational awareness is a skill necessary to both ground and in-flight operations
  • Knowing where you are & where other traffic is operating
  • Knowing where you will be and where other traffic will be
  • Recognize High Hazard Areas:
    • Airways, especially near VORs, and Class B, Class C, Class D, and Class E surface areas are places where aircraft tend to cluster
    • Remember, most collisions occur during days when the weather is good
      • Being in a "radar environment" still requires vigilance to avoid collisions
  • Listening and looking: the Good Senses
  • All available information (FAR 91.103)
  • "Head's Down" decreases situational awareness - minimize as much as possible
  • Common Problems: When are you doing checklists? Do you have taxi diagrams when you land? Are your radios preset when you are "in-range?" Do you ensure you have weather before you land?

Scanning
Figure 1: Scanning
Collision Avoidance Checklist
Figure 2: Collision Avoidance Checklist

Visual Scanning:

  • Scanning is a continuous process used by the pilot and copilot (or right seat passenger) to cover all areas of the sky visible from the cockpit
  • Pilots must develop an effective scanning technique which maximizes one's visual capabilities
  • Since the brain is already trained to process sight information that is presented from left to right, one may find it easier to start scanning over the left shoulder and proceed across the windshield to the right
  • FAR 91.113(b): When in VMC, it's pilot's responsibility to see and avoid
  • Scan should be broken down into about 10° increments, spending about 1 second on each segment
  • During VMC: 75-80% of time looking outside, 20-25% spent scanning instruments
  • When moving eyes from inside to outside, or vice versa, give eyes time to adjust
  • Age, Dust, Haze, Rain, Glare, and a dirty windscreen all impede ability to scan
  • Blind spots: wings, struts, etc
  • If Aircraft doesn't appear to move, you may be on collision course with it
    • Waiting for the aircraft to increase or decrease in size could prove costly
  • If Aircraft is above horizon, it's probably above you
  • If Aircraft is below horizon, it's probably below you
  • If Aircraft is level with horizon, it's at your altitude
  • The eye can see 200° at a time
  • Must focus the eye at 10° increments at a time, about a second or 2 when looking for traffic
  • Visibility Conditions: smoke, haze, dust, rain, and flying toward the sun reduce your ability to detect objects or birds
  • Windshield Conditions: dirty or bug-smeared windshields reduce outside visibility
  • Visual Obstructions:
    • Pilots need to move their heads to see around blind spots caused by fixed aircraft structures, such as door posts, wings, etc
    • It will be necessary at times to maneuver the aircraft; e.g., lift a wing, to facilitate seeing
    • Pilots must ensure curtains and other cockpit objects; e.g., maps on glare shield, are removed and stowed during flight
  • Vision can be effected by different levels of illumination:
    • Bright Illumination: reflected off clouds, water, or snow, and desert terrain that produces glare resulting in eye strain
    • Dim Illumination: small print and colors on aeronautical charts and aircraft instruments become unreadable
    • Dark Adaptation: Eyes must have at least 20 to 30 minutes to adjust to reduced light conditions
      • Red light helps night vision however distorts color
      • Impaired by exposure to cabin pressure altitudes above 5000', carbon monoxide inhaled in smoking and from exhaust fumes, deficiency of Vitamin A in diet and by prolonged exposure to bright sunlight
      • Light adaptation can be destroyed in seconds, closing one eye may preserve some
  • While the eyes can observe an approximate 200° arc of the horizon at one glance, only a very small center area called the fovea, in the rear of the eye, has the ability to send clear, sharply focused messages to the brain
    • All other visual information that is not processed directly through the fovea will be of less detail
    • An aircraft at a distance of 7 miles which appears in sharp focus within the foveal center of vision would have to be as close as 7/10 of a mile in order to be recognized if it were outside of foveal vision
    • Thus, one must use timesharing techniques to efficiently scan the surrounding airspace while monitoring instruments as well
    • Because the eyes can focus only on this narrow viewing area, effective scanning is accomplished with 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
    • Although horizontal back-and-forth eye movements seem preferred by most pilots, each pilot should develop a scanning pattern that is most comfortable and then adhere to it to assure optimum scanning
  • Studies show that the time a pilot spends on visual tasks inside the cabin should represent no more that 1/4 to 1/3 of the scan time outside, or no more than 4 to 5 seconds on the instrument panel for every 16 seconds outside
  • Pilots should realize that their eyes may require several seconds to refocus when switching views between items in the cockpit and distant objects. The eyes will also tire more quickly when forced to adjust to distances immediately after close-up focus, as required for scanning the instrument panel. Eye fatigue can be reduced by looking from the instrument panel to the left wing past the wing tip to the center of the first scan quadrant when beginning the exterior scan. After having scanned from left to right, allow the eyes to return to the cabin along the right wing from its tip inward. Once back inside, one should automatically commence the panel scan
  • Effective scanning also helps avoid "empty field myopia

Scanning for Other Aircraft:

  • Scanning the sky for other aircraft is a key factor in collision avoidance. It should be used continuously by the pilot and copilot (or right seat passenger) to cover all areas of the sky visible from the cockpit. Although pilots must meet specific visual acuity requirements, the ability to read an eye chart does not ensure that one will be able to efficiently spot other aircraft. Pilots must develop an effective scanning technique which maximizes one’s visual capabilities. The probability of spotting a potential collision threat obviously increases with the time spent looking outside the cockpit. Thus, one must use timesharing techniques to efficiently scan the surrounding airspace while monitoring instruments as well
  • While the eyes can observe an approximate 200 degree arc of the horizon at one glance, only a very small center area called the fovea, in the rear of the eye, has the ability to send clear, sharply focused messages to the brain. All other visual information that is not processed directly through the fovea will be of less detail. An aircraft at a distance of 7 miles which appears in sharp focus within the foveal center of vision would have to be as close as 7/10 of a mile in order to be recognized if it were outside of foveal vision. Because the eyes can focus only on this narrow viewing area, effective scanning is accomplished with 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 degrees, and each area should be observed for at least 1 second to enable detection. Although horizontal back-and-forth eye movements seem preferred by most pilots, each pilot should develop a scanning pattern that is most comfortable and then adhere to it to assure optimum scanning
  • Studies show that the time a pilot spends on visual tasks inside the cabin should represent no more that 1/4 to 1/3 of the scan time outside, or no more than 4 to 5 seconds on the instrument panel for every 16 seconds outside. Since the brain is already trained to process sight information that is presented from left to right, one may find it easier to start scanning over the left shoulder and proceed across the windshield to the right
  • Pilots should realize that their eyes may require several seconds to refocus when switching views between items in the cockpit and distant objects. The eyes will also tire more quickly when forced to adjust to distances immediately after close-up focus, as required for scanning the instrument panel. Eye fatigue can be reduced by looking from the instrument panel to the left wing past the wing tip to the center of the first scan quadrant when beginning the exterior scan. After having scanned from left to right, allow the eyes to return to the cabin along the right wing from its tip inward. Once back inside, one should automatically commence the panel scan
  • Effective scanning also helps avoid “emptyfield myopia.” This condition usually occurs when flying above the clouds or in a haze layer that provides nothing specific to focus on outside the aircraft. This causes the eyes to relax and seek a comfortable focal distance which may range from 10 to 30 feet. For the pilot, this means looking without seeing, which is dangerous

Cockpit Management

  • Studying maps, checklists, and manuals before flight, with other proper preflight planning; e.g., noting necessary radio frequencies and organizing cockpit materials, can reduce the amount of time required to look at these items during flight, permitting more scan time

Visual Separation:

  • Visual separation is a means employed by ATC to separate aircraft in terminal areas and en route airspace in the NAS
  • There are two methods employed to effect this separation:
    • The tower controller sees the aircraft involved and issues instructions, as necessary, to ensure that the aircraft avoid each other
    • A pilot sees the other aircraft involved and upon instructions from the controller provides separation by maneuvering the aircraft to avoid it. When pilots accept responsibility to maintain visual separation, they must maintain constant visual surveillance and not pass the other aircraft until it is no longer a factor
      • NOTE: Traffic is no longer a factor when during approach phase the other aircraft is in the landing phase of flight or executes a missed approach; and during departure or en route, when the other aircraft turns away or is on a diverging course
  • A pilot's acceptance of instructions to follow another aircraft or provide visual separation from it is an acknowledgment that the pilot will maneuver the aircraft as necessary to avoid the other aircraft or to maintain in-trail separation. In operations conducted behind heavy jet aircraft, it is also an acknowledgment that the pilot accepts the responsibility for wake turbulence separation
    • NOTE: When a pilot has been told to follow another aircraft or to provide visual separation from it, the pilot should promptly notify the controller if visual contact with the other aircraft is lost or cannot be maintained or if the pilot cannot accept the responsibility for the separation for any reason
  • Scanning the sky for other aircraft is a key factor in collision avoidance. Pilots and copilots (or the right seat passenger) should continuously scan to cover all areas of the sky visible from the cockpit. Pilots must develop an effective scanning technique which maximizes one's visual capabilities. Spotting a potential collision threat increases directly as more time is spent looking outside the aircraft. One must use timesharing techniques to effectively scan the surrounding airspace while monitoring instruments as well
  • Since the eye can focus only on a narrow viewing area, effective scanning is accomplished with 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 ten degrees, and each area should be observed for at least one second to enable collision detection. Although many pilots seem to prefer the method of horizontal back-and-forth scanning every pilot should develop a scanning pattern that is not only comfortable but assures optimum effectiveness. Pilots should remember, however, that they have a regulatory responsibility (14 CFR Section 91.113(a)) to see and avoid other aircraft when weather conditions permit
  • Pilot:

    • Acceptance of instructions to follow another aircraft or to provide visual separation from it is an acknowledgment that the pilot will maneuver the aircraft as necessary to avoid the other aircraft or to maintain in-trail separation. Pilots are responsible to maintain visual separation until flight paths (altitudes and/or courses) diverge
    • If instructed by ATC to follow another aircraft or to provide visual separation from it, promptly notify the controller if you lose sight of that aircraft, are unable to maintain continued visual contact with it, or cannot accept the responsibility for your own separation for any reason
    • The pilot also accepts responsibility for wake turbulence separation under these conditions
  • Controller:

    • Within the terminal area when a controller has both aircraft in sight or by instructing a pilot who sees the other aircraft to maintain visual separation from it
    • Pilots are responsible to maintain visual separation until flight paths (altitudes and/or courses) diverge
    • Within en route airspace when aircraft are on opposite courses and one pilot reports having seen the other aircraft and that the aircraft have passed each other

Use of Visual Clearing Procedures:

  • Before Takeoff:

    • Prior to taxiing onto a runway or landing area in preparation for takeoff, pilots should scan the approach areas for possible landing traffic and execute the appropriate clearing maneuvers to provide them a clear view of the approach areas
  • Climbs and Descents:

    • During climbs and descents in flight conditions which permit visual detection of other traffic, pilots should execute gentle banks, left and right at a frequency which permits continuous visual scanning of the airspace about them
  • Straight and Level:

    • Sustained periods of straight and level flight in conditions which permit visual detection of other traffic should be broken at intervals with appropriate clearing procedures to provide effective visual scanning
    • Scan left to right or right to left, but develop some sort of pattern
  • Turns:

    • High Wing: Momentarily raise the wing in the direction of turn to look for traffic
    • Low Wing: Lower the wing in the direction of turn and scan all the way across the turn both forward and in the direction of the turn
  • Traffic Pattern:

    • Entries into traffic patterns while descending create specific collision hazards and should be avoided
    • Concentrate your scan mostly on the side of the runway that the pattern is on as you would expect most traffic to be there
      • Tower should give you situational awareness to potential hazard traffic
      • Remember traffic, especially at an uncontrolled field could be anywhere
    • Entry at a 45° angle or on an extended leg (whichever is most practical) will provide the best view of the pattern
  • Traffic at VOR Sites:

    • All operators should emphasize the need for sustained vigilance in the vicinity of VORs and airway intersections due to the convergence of traffic
  • Training Operations:

    • Operators of pilot training programs are urged to adopt the following practices:
      • Pilots undergoing flight instruction at all levels should be requested to verbalize clearing procedures (call out “clear” left, right, above, or below) to instill and sustain the habit of vigilance during maneuvering
      • 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

Additional Methods:

  • Use radar services, TCAS, ADS-B, GPS, Mode S/TIS
  • ATC facilities often provide radar traffic advisories on a workload-permitting basis
    • Use this support whenever possible or when required
  • FAR 91.126(b) - Operating near Airports in Class G Airspace - When approaching to land at an airport without an operating control tower... each pilot of an airplane must make all turns of that airplane to the left [unless otherwise designated]
  • FAR 91.127(a) - Operating near Airports in Class E Airspace - When operating in the vicinity of an airport in Class E airspace, comply with FAR 91.126
  • FAR 91.119 Minimum Safe Altitudes:
    • An altitude which will allow a safe emergency landing without hazard to people or property on the surface
    • Congested Area - 1000' above the highest obstacle within 2,000' or the aircraft
    • Other than congested areas - 500'
    • Over water & sparsely populated areas: no closer than 500' to any person, vessel, vehicle or structure
  • Pilots should be familiar with rules on right-of-way, so if an aircraft is on an obvious collision course, one can take immediate evasive action, preferably in compliance with applicable Federal Aviation Regulations
    • The decision to climb, descend, or turn is a matter of personal judgment, but one should anticipate that the other pilot may also be making a quick maneuver
    • Watch the other aircraft during the maneuver and begin your scanning again immediately since there may be other aircraft in the area
  • When meteorological conditions permit, regardless of type of flight plan or whether or not under control of a radar facility, the pilot is responsible to see and avoid other traffic, terrain, or obstacles

  • The eye requires time to accommodate to looking at objects of different color and distance
  • Empty field myopia: inability of eye to focus; occurs when there is a lack of visual reference
    • Occurs when we stare but see nothing
  • An object seen in one eye but obscured from another may cause us not to "accept" it
  • Our eyes accept light from a 200° arc but can only focus on 10-15 often leading to tunnel vision
  • Blossom effect: objects at a distance appear stationary but will suddenly bloom into a huge mass when they get close

Scan Patterns:

  • Follow these basic principles:
    1. Look outside the airplane to see where you are going
    2. Look at the aircraft with respect to the horizon to check and maintain a desired attitude
    3. Look inside the aircraft at the instrument panel to check for proper power settings, flight instrument readings and for any signs of engine malfunction

Side-To-Side Scan Pattern
Figure 3: Side-to-Side Scan Pattern
Collision Avoidance Checklist
Figure 4: Middle-to-Side Scan Pattern

Judgment Aspects of Collision Avoidance:

  • Introduction. The most important aspects of vision and the techniques to scan for other aircraft are described in paragraph 8−1−6, Vision in Flight. Pilots should also be familiar with the following information to reduce the possibility of mid-air collisions
  • Determining Relative Altitude. Use the horizon as a reference point. If the other aircraft is above the horizon, it is probably on a higher flight path. If the aircraft appears to be below the horizon, it is probably flying at a lower altitude
  • Taking Appropriate Action. Pilots should be familiar with rules on right-of-way, so if an aircraft is on an obvious collision course, one can take immediate evasive action, preferably in compliance with applicable Federal Aviation Regulations
  • Consider Multiple Threats. The decision to climb, descend, or turn is a matter of personal judgment, but one should anticipate that the other pilot may also be making a quick maneuver. Watch the other aircraft during the maneuver and begin your scanning again immediately since there may be other aircraft in the area
  • Collision Course Targets. Any aircraft that appears to have no relative motion and stays in one scan quadrant is likely to be on a collision course. Also, if a target shows no lateral or vertical motion, but increases in size, take evasive action
  • Recognize High Hazard Areas:
    • Airways, especially near VORs, and Class B, Class C, Class D, and Class E surface areas are places where aircraft tend to cluster
    • Remember, most collisions occur during days when the weather is good. Being in a “radar environment” still requires vigilance to avoid collisions
  • Cockpit Management. Studying maps, checklists, and manuals before flight, with other proper preflight planning; e.g., noting necessary radio frequencies and organizing cockpit materials, can reduce the amount of time required to look at these items during flight, permitting more scan time
  • Windshield Conditions. Dirty or bugsmeared windshields can greatly reduce the ability of pilots to see other aircraft. Keep a clean windshield
  • Visibility Conditions. Smoke, haze, dust, rain, and flying towards the sun can also greatly reduce the ability to detect targets
  • Visual Obstructions in the Cockpit:
    • Pilots need to move their heads to see around blind spots caused by fixed aircraft structures, such as door posts, wings, etc. It will be necessary at times to maneuver the aircraft; e.g., lift a wing, to facilitate seeing
    • Pilots must ensure curtains and other cockpit objects; e.g., maps on glare shield, are removed and stowed during flight
  • Aircraft Lighting:

    • Operation Lights On:

      • Day or night, use of exterior lights can greatly increase the conspicuity of any aircraft (cheap insurance!)
      • Private pilot test says required within 10nm of airport
      • Keep interior lights low at night
      • Use of anti-collision lighting required at night, use it always except in clouds
      • Beacon on anytime engine is running
      • Use of position lights at night, FAR 91.209
      • Most airline operations manuals all exterior lighting on when below FL180
      • GOAL: Be as visible as possible
  • Air Traffic Control Support:

    • ATC facilities often provide radar traffic advisories on a workload-permitting basis
    • Flight through Class C and Class D airspace requires communication with ATC
    • Use this support whenever possible or when required
    • Provides radar traffic information to radar identified aircraft operating outside positive control airspace on a workload permitting basis
    • Additionally, controllers may issue safety alerts to aircraft under their control if aware the aircraft is at an altitude believed to place the aircraft in unsafe proximity to terrain, obstructions, or other aircraft

Communication:

  • ICS: "clear left, clear right" as appropriate

References: