Visual Scanning & Collision Avoidance

Introduction:

  • Visual scanning and collision avoidance are two responsibilities of the pilot in command
  • 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 pilot's vision and techniques to scan for other aircraft are paramount
    • FAR 91.113(b) "See and Avoid" ...When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft to see and avoid other aircraft
  • To mitigate limits of human performance, the aviation industry (endorsed by the FAA) built additional methods/tools for pilots to augment visual scanning

Visual Scanning Vs. Collision Avoidance:

  • Visual scanning is the consistent scan to avoid hazards, known or unknown to a pilot
  • Collision avoidance is the action taken to avoid obstacles by observing and conducting a thorough preflight
    • Collision avoidance involves looking for obstacles during ground reference maneuvers, as well as map studies before and during flight, as well as during ground operations
  • Note that while visual scanning requires Visual Meteorological Conditions (VMC), collision avoidance is a continuous effort that starts in preflight and ends only when the engine is shut down

Situational Awareness:

  • Situational awareness is a skill necessary for 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 on 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
    Scanning
  • Scanning
    Scanning
  • Collision Avoidance Checklist
    Collision Avoidance Checklist
  • Collision Avoidance Checklist
    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 that maximizes one's visual capabilities
  • FAR 91.113(b): When in VMC, it's the pilot's responsibility to see and avoid
  • The scan should be broken down into about 10° increments, spending about 1 second on each segment
  • During VMC: 75-80% of the time looking outside, 20-25% spent scanning instruments
  • When moving eyes from inside to outside, or vice versa, give eyes time to adjust
  • The eye can see 200° at a time
  • Must focus the eye at 10° increments at a time, about a second or two when looking for traffic
  • Vision can be affected 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 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, can 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 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
    • 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 ensure optimum scanning
  • 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, and to the center of the first scan quadrant when beginning the exterior scan. After scanning 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"
  • Barriers to Visual Scanning:

    • Windshield Conditions:

      • Dirty or bug-smeared windshields reduce outside visibility
      • The eye will be distracted by spots on the windscreen
      • The eye will have difficulty focusing on distant objects with several near objects in the way
    • Blind Spots:

      • Pilots must move their heads to see around blind spots caused by fixed aircraft structures, such as door posts, wings, struts, 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 the glare shield, are removed and stowed during flight
    • Visibility Conditions:

      • Smoke, haze, dust, rain, and flying toward the sun (glare) reduce your ability to detect objects or birds
      • This can be mitigated by using visors [Amazon] or sunglasses [Amazon]
    • The Pilot:

      • Eyes are only as good as they are
      • Age and fatigue all take their toll
  • Visual Scanning Patterns:

    • Side-To-Side Scan Pattern
      Side-to-Side Scan Pattern
    • Collision Avoidance Checklist
      Middle-to-Side Scan Pattern
    • 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 determine the relative altitude
        • Use the horizon as a reference point:
          • If an aircraft is above horizon it's probably above you
          • If an aircraft is below horizon it's probably below you
          • If an aircraft is level with horizon it's at your altitude
          • 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
            • Waiting for the aircraft to increase or decrease in size could prove costly
      3. Look inside the aircraft at the instrument panel to check for proper power settings, flight instrument readings, and any signs of engine malfunction
    • Side-To-Side Scan Pattern
      Side-to-Side Scan Pattern
    • Collision Avoidance Checklist
      Middle-to-Side Scan Pattern

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 that 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° arc of the horizon at one glance, only a very small center area called the fovea, in the rear of the eye, can 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 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 ensure optimum scanning
  • Studies show that the time a pilot spends on visual tasks inside the cabin (cockpit management/scanning) should represent at most 1/4 to 1/3 of the scan time outside or 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, and to the center of the first scan quadrant when beginning the exterior scan. After scanning 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." 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, ranging from 10 to 30 feet. For the pilot, this means looking without seeing, which is dangerous
  • Pay attention to other traffic at all times, but especially when the risk for midair is statistically higher:
    • Within five nautical miles of an airport;
    • In daylight visual flight rules conditions, and;
    • At or below 3,000 feet above ground level
  • Additional tips include verifying ATC calls are accurate, turning on lights, and questioning any conflict or confusion

Flight Deck Management:

  • Practicing cockpit management techniques such as 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 for maintaining 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 the 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 critical factor in collision avoidance. Pilots and copilots (or the right-seat passengers) should continuously scan to cover all areas of the sky visible from the cockpit. Pilots must develop an effective scanning technique that 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
  • Although many pilots prefer the method of horizontal back-and-forth scanning, every pilot should develop a scanning pattern that is not only comfortable but also 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 for maintaining 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:

    • Controllers apply visual separation only when:
      • 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 for maintaining 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:

    • Before 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 that permit visual detection of other traffic, pilots should execute gentle banks, left and right, at a frequency that permits continuous visual scanning of the airspace around them
  • Straight and Level:

    • Sustained periods of straight and level flight in conditions that 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 pattern
  • Turns:

    • High Wing: Momentarily raise the wing in the direction of the 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
      • The tower should give you situational awareness of 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
  • Scanning Techniques for Traffic Avoidance:

    • Pilots must be aware of the limitations inherent in the visual scanning process. These limitations may include:
      • Reduced scan frequency due to concentration on flight instruments or tablets and distraction from passengers
      • Blind spots related to high-wing and low-wing aircraft, in addition to windshield posts and sun visors
      • Prevailing weather conditions, including reduced visibility and the position of the sun
      • The attitude of the aircraft will create additional blind spots
      • The physical limitations of the human eye, including the time required to (re)focus on near and far objects, from the instruments to the horizon, for example, empty field myopia, narrow field of vision, and atmospheric lighting, all affect our ability to detect another aircraft
    • Best practices to see and avoid:
      • ADS-B In is an effective system to help pilots see and avoid other aircraft. If your aircraft is equipped with ADS-B In, it is important to understand its features and how to use it properly. Many units provide visual and/or audio alerts to supplement the system's traffic display. Pilots should incorporate the traffic display in their normal traffic scan to provide awareness of nearby aircraft. Before taxiing onto an airport movement area, ADS-B In can provide an advance indication of arriving aircraft and aircraft in the traffic pattern. Systems incorporating a traffic-alerting feature can help minimize the pilot's inclination to fixate on the display. Refer to 4-5-7e, ADS-B Limitations
      • Understand the limitations of ADS-B In. In certain airspace, not all aircraft will be equipped with ADS-B Out or transponders and will not be visible on your ADS-B In display
      • Limit the amount of time that you focus on flight instruments or tablets
      • Develop a strategic approach to scanning for traffic. Scan the entire sky and try not to focus straight ahead

Additional Methods/Tools:

  • 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
  • The eye requires time to accommodate to looking at objects of different colors and distance
  • Empty field myopia: the inability of the 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

Judgment Aspects of Collision Avoidance:

  • Remember cruising altitudes based on direction
  • 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
  • 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
  • Aircraft Lighting:

    • Operation Lights On:

      • Day or night, the use of exterior lights can greatly increase the conspicuity of any aircraft (cheap insurance!)
      • Keep interior lights low at night
      • Use of anti-collision lighting required at night, use it always except in clouds
      • Beacon on any time the engine is running
      • Use of position lights at night, FAR 91.209
      • Most airline operations manuals all exterior lighting on when below FL180
      • The goal is to 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
    • Some pilots have questioned ATC when receiving an amended clearance and requested "traffic information" and were at a loss when the reply indicated "no traffic report"
      • In such cases, the controller has taken action to prevent a traffic conflict that would have occurred at a distant point

Communication:

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

Obstructions to Flight:

  • Many structures exist that could significantly affect the safety of your flight when operating below 500' AGL and particularly below 200' AGL, despite FAR 91.119 allowing flight below 500' when over sparsely populated areas or open water
  • Obstacles that extend more than 200 feet AGL are typically shown on sectional charts unless they are within the yellow tint of a city
  • At and below 200' AGL, you are operating close to power lines, antenna towers, etc., which may or may not be lit
  • Notice to Air Missions (NOTAMs) will typically be published for unlit structures, but pilot vigilance is imperative in case the FAA has not yet been notified of outages
  • Antenna Towers:

    • Communication Antennas
      Communication Antennas
    • Numerous skeletal structures, such as radio and television antenna towers, exceed 1,000' or 2,000' AGL
    • Most skeletal structures are supported by guy wires, which are very difficult to see in good weather and can be invisible at dusk or during periods of reduced visibility
    • These wires can extend about 1,500 feet horizontally from a structure; therefore, all skeletal structures should be avoided horizontally by at least 2,000 feet
    • Additionally, new towers may not be on your current chart because the information was not received prior to the printing of the chart
  • Overhead Wires:

    • Transmission and utility lines often span approaches to runways and natural flyways, such as lakes, rivers, gorges, and canyons, and cross other landmarks pilots frequently follow, such as highways, railroad tracks, etc.
    • Supporting structures such as guy wires exist here as well
    • Some locations identify these obstructions with unique sequencing flashing white strobe light systems
      • However, many power lines do not require notice to the FAA and, therefore, are not marked and/or lighted
      • Many of those that do require notice do not exceed 200 feet AGL or meet the Obstruction Standard of 14 CFR Part 77 and, therefore, are not marked and/or lighted
    • Pilots are cautioned to remain extremely vigilant, especially in the case of seaplane and/or float-equipped aircraft
  • Wind Turbines:

    • Sectional Depiction of Wind Farms
      Sectional Depiction of Wind Farms
    • Wind turbines are becoming increasingly preveland as one method in the shift to renewable energy
    • >
    • Wind turbines are typically below 500 feet, but some may be significantly higher, even encroaching into Class E airspace
    • >
    • Turbines or groups of turbines (1 out of 3 must be lit) have red flashing lights placed on top of the turbine nacelle (note the blade is higher)
    • >
    • Additionally, wind farms can produce reflectivity, producing returns on dopplar radar
    • >
    • Wind farms are depicted on sectional charts with a boxed number indicating the maximum elevation figure
    • >
    • Sectional Depiction of Wind Farms
      Sectional Depiction of Wind Farms
      >
  • Unmanned Balloons:

    • Sectional Chart Key West Surveillance Balloon
      Key West Balloon Hazard
    • The majority of unmanned free balloons currently being operated have, extending below them, either a suspension device to which the payload or instrument package is attached, or a trailing wire antenna, or both
    • Good judgment on the part of the pilot dictates that aircraft should remain well clear of all unmanned free balloons, and flight below them should be avoided at all times
    • Pilots are urged to report any unmanned free balloons sighted to the nearest FAA ground facility with which communication is established to assist FAA ATC facilities in identifying and flight-follow unmanned free balloons operating in the airspace
    • Sectional Chart Key West Surveillance Balloon
      Key West Balloon Hazard

Conclusion:

  • Visual scanning and collision avoidance is part of every flight, from when you start the engine to when you turn it off
  • 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
  • When weather conditions permit, during the time an IFR flight is operating, it is the direct responsibility of the pilot to avoid other aircraft since VFR flights may be operating in the same area without the knowledge of ATC
    • Traffic clearances provide standard separation only between IFR flights. to see and avoid other traffic, terrain, or obstacles
  • It is a constant task, and the more eyes, the better, so utilize crew resource management as part of every flight
  • There are other objects or structures that could adversely affect your flight, such as construction cranes near an airport, newly constructed buildings, new towers, etc.
  • Many of these structures do not meet charting requirements or may not yet be charted because of the charting cycle
  • Some structures do not require obstruction marking and/or lighting, and some may not be marked and lighted even though the FAA recommended it
  • See also:
  • Remember your minimum safe altitudes
  • The AOPA offers a collision avoidance safety spotlight course
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References: