Aviation Visual Perception

Randy Gibb, Rob Gray, Lauren Scharff

• Publisher: Routledge
• Year: 2016
• ISBN:
  9781317176589
• Edition: 1
• Topic: Tecnología e ingeniería
• Subtopic: Transporte y navegación

Vision is the dominant sense used by pilots and visual misperception has been identified as the primary contributing factor in numerous aviation mishaps, resulting in hundreds of fatalities and major resource loss. Despite physiological limitations for sensing and perceiving their aviation environment, pilots can often make the required visual judgments with a high degree of accuracy and precision. At the same time, however, visual illusions and misjudgments have been cited as the probable cause of numerous aviation accidents, and in spite of technological and instructional efforts to remedy some of the problems associated with visual perception in aviation, mishaps of this type continue to occur. Clearly, understanding the role of visual perception in aviation is key to improving pilot performance and reducing aviation mishaps. This book is the first dedicated to the role of visual perception in aviation, and it provides a comprehensive, single-source document encompassing all aspects of aviation visual perception. Thus, this book includes the foundations of visual and vestibular sensation and perception; how visual perceptual abilities are assessed in pilots; the pilot's perspective of visual flying; a summary of human factors research on the visual guidance of flying; examples of specific visual and vestibular illusions and misperceptions; mishap analyses from military, commercial and general aviation; and, finally, how this knowledge is being used to better understand visual perception in aviation's next generation. Aviation Visual Perception: Research, Misperception and Mishaps is intended to be used for instruction in academia, as a resource for human factors researchers, design engineers, and for instruction and training in the pilot community.

Chapter 1
Vision in Aviation

Veridical perception of visual cues is necessary for spatial orientation and controlling our movements as we navigate within our environment. Driving and athletics are two arenas with which everyone can associate in terms of visually guided behavior and successful execution of desired goals. In typical daily life our interface with the environment consists of our feet on or near the ground, movements in the left-right and/or fore-aft direction as well as a one-gravitational force (1-G) acting vertically on our bodies with the horizon straight ahead. The interpretation of visual cues from the environment and the perception of vestibular inputs as we maneuver ourselves are founded on these typical constants, leading to confidence about where our feet are, where the horizon is, and which is “up.”

Aviation, however, allows the human operator to accomplish visually guided actions not experienced anywhere else. With the additional spatial dimension of altitude and the possibility of extreme vertical movement, combined with potential extreme velocities and accelerations in the left-right and fore-aft directions, flying poses challenges to humans that are not faced in other domains. When flying, obtaining and maintaining spatial orientation is predominantly accomplished by the visual system. Thus, while flying 30 m (100 ft) above the ground at high speeds or controlling the aircraft for a night visual approach to landing, pilots must accurately perceive and interpret environmental cues with their eyes. Herein lies the problem; the human body is not physiologically prepared to cope with these extreme and sometimes violent movements and forces that occur in aviation. These visual perception challenges must be recognized and appreciated by pilots and aviation researchers.

Despite physiological limitations for sensing and perceiving their aviation environment, pilots can often make the required visual judgments with a high degree of accuracy and precision. At the same time, however, visual illusions and misjudgments have been cited as the probable cause of numerous aviation accidents, and in spite of technological and instructional efforts to remedy some of the problems associated with visual perception in aviation, mishaps of this type continue to occur. Clearly, understanding the role of visual perception in aviation is key to improving pilot performance and reducing aviation mishaps. Furthermore, with the implementation of enhanced and synthetic visual systems, the next generation of aviation is banking heavily on knowledge of visual perception.

Over the years numerous articles, pamphlets, and books have been written on the topics of spatial disorientation and visual illusions in aviation (e.g., Benson, 1988; Cocquyt, 1953; Kern, 2002; Kraft and Elworth, 1969; Lessard, 2000; Newman, 2005; Ostinga et al., 1999; Pitts, 1967; Previc, 2004; Schiff, 1990 and 1994; Wulfeck, Weisz, and Raben, 1958; as well as the Federal Aviation Administration flying safety pamphlets, military flying manuals). In 2007 the Australian Transport Safety Bureau published An overview of spatial disorientation as a factor in aviation accidents and incidents. Also, magazines have dedicated entire issues to the subject. For instance, IEEE Engineering in Medicine and Biology, in their March/April 2000 edition, addressed aeronautical illusions, and the Naval Aviation magazine, Approach, in May/June 2004, did the same.

This book intends to update and synthesize the previous work to provide the reader with a single resource for comprehensive and detailed explanations of visual disorientation as well as the physiological and perceptual background of the visual system associated with aviation-related perceptual illusions. Vestibular physiology and disorientation is also presented as it is highly integrated with our body’s spatial orientation system. Examples of aircraft accidents are included to illustrate failed visual perception and spatial orientation and to demonstrate that pilots have been and are still today far too confident in their limited visual perceptual capabilities when flying. It is not the intent to disparage any of the pilots involved but rather to ensure that others learn from their experiences. The objective of this book is to help educate pilots and others regarding the seduction of visual misperception, with the intention to provide not only a resource for pilots but also a starting point for further research into aviation visual perception.

The Challenge

Visual perception within aviation is not well understood (Calvert, 1950; Havron, 1962; Warren and Owen, 1982; Mulder, et al. 2000), and there is still much to be learned about visual perception in general. While our subjective experience leads us to believe that our brain has access to a perfect, high-definition image of the outside world, Smallman and St. John (2005) point out that this “naïve realism” is simply not consistent with what is known about the human visual system. In actuality, visual perception is “sparse and sewn together” and assumptions must be made to simplify complex scenes that “distort interpretation and result in imperfect, just-in-time, just-good-enough approximations of reality” (p. 8). Perception can be thought of as a series of educated guesses regarding the outside world rather than the detection of what is there with 100 percent accuracy and certainty. The brain sometimes guesses wrong, resulting in visual illusions. Small and St. John summarized these points nicely:

The illusion of objectivity is that the ubiquity of these errors goes unobserved, thereby fostering and maintaining naïve realism. The brain is a master at concealing its tricks, and only occasionally does one get to glimpse the real Wizard of Oz behind the curtain. (p. 9)

This lack of veridicality makes the challenge of understanding visual perception an incredibly complex endeavor. Because perception does not involve a perfect 1:1 representation of the external environment, we cannot understand how vision works simply by investigating the basic physical characteristics of the world. Knowing that a runway is 3,000 m long × 50 m wide tells us little about how a pilot will perceive this object, because the visual system does not even use these units. Thus, while the physiology of the eye and the study of optics are straightforward and well understood, higher-level visual processes such as understanding how a three-dimensional (3D) world is recreated from a two-dimensional (2D) retinal image are still not completely understood (Smallman and St. John, 2005).

A further challenge to understanding the role of vision in aviation arises from the fact that the pilot is a part of a complex human-machine-environment system (illustrated in Figure 1.1), in which there are numerous, complex interactions between the factors of the environment, the pilot, and the aircraft. Environmental factors such as weather, time of day, geographic location, and G-forces can directly alter a pilot’s perception of the world (e.g., by reducing visibility), and/or change the way in which visual cues are used to control the aircraft (e.g., by altering the amount airspeed changes for a given stick movement). The pilot adds both capabilities and potential liabilities into the system. The pilot’s skill, proficiency, training, and experience are all factors that increase overall system success. However, if a pilot is not prepared for a particular flight (e.g., is lacking in motivation, personal life stressors or fatigued), the environment can quickly expose a pilot’s vulnerabilities. The aircraft in the system has certain characteristics and limitations given its particular design, including properties such as aircraft manuals, procedures, the level of automation, displays, controls, warnings and alarm systems, redundancy in emergency systems, and the overall interface design.

Figure 1.1 Environment, pilot, and aircraft interaction

Chapter 6 presents a detailed summary of visual perception illusions and spatial disorientations. Aviation accident examples involving visual misperception are given in Chapter 7. To help introduce misperception in aviation, below is a fairly recent mishap that highlights several issues within aviation visual perception: the misperception of height and distance, the meteorological limitation of night (lack of visual cues), and the physiological limitation of a color deficiency. Increased awareness of both the visual phenomenon of misperception of height and distance as well as night flying hazards are major themes of this book.

Aviation Mishap Involving Visual Misperceptions

July 26, 2002, prior to sunrise, a Boeing 727, operated by a commercial freight carrier, struck trees during a short final approach and crashed 472 m (1,550 ft) short of runway 09 at Tallahassee Regional Airport (National Transportation Safety Board [NTSB] report, 2002). Three crew members were seriously injured and the airplane was destroyed. Although there were many interesting aspects of this particular mishap, detail will only be presented on aspects of the visual factors contributing to the accident.

The flight had departed Memphis, TN, for Tallahassee and operated on an instrument flight plan. The forecast weather for the arrival destination was night visual meteorological conditions. The crew had debated whether to land on runway 27 with an Instrument Landing System (ILS, precision glide-path approach) or the more conveniently aligned visual approach to runway 09, and had decided to use runway 09. Runway 09 did have Precision Approach Path Indicator (called PAPIs) lights available to assist in glide-path control. As the pilot maneuvered the airplane into alignment with the runway, the descent rate of the aircraft increased beyond the 3-degree desired glide-path. According to the Flight Safety Foundation report (2005), the profile view of the approach had the concave shape characteristic of the black-hole illusion as illustrated in Figure 1.2. The PAPI lights are also depicted in Figure 1.2, showing how they visually inform pilots of their glide-path.

Although a more detailed discussion of the black-hole illusion occurs in the chapter on visual illusions and misperception (Chapter 6), to better understand this mishap it is briefly explained. When a pilot approaches a runway that lacks terrain features and other ambient visual cues during a dark night, the only visual referent is the lighted runway shape. This approach-and-landing environment makes it very difficult for a pilot to estimate height above and distance to the runway. Due to the lack of terrain features the pilot perceives the plane to be higher and farther from the runway than it actually is and, consequently, initiates an unwarranted descent below the normal glide-path. In this scenario a pilot will realize far too late that the plane is on an extremely shallow approach angle to the runway and dangerously low; controlled flight into terrain often results. Other phrases used are “landing short” or “under-shooting” the runway. The profile view of this type of approach glide-path has a concave shape due to the excessive descent rate that then shallows out as the pilot approaches the landing runway (shown in Figure 1.3).

Figure 1.2 Mishap glide-path

Source: From NTSB report, 2002.

In the case of the accident in Florida, upon examining the profile of the aircraft’s descent, one could argue the black-hole illusion caused the pilot to misperceive the glide-slope starting at 10.2 km (5.5 nautical miles) from the runway until impact. The final approach to runway 09 required the aircraft to fly over a national forest area which had no lights or terrain features (FSF report, 2005). Prior to impact the airplane was flying at 270 km/hr (146 knots) airspeed with a descent rate of 161 m/min (528 ft/min), but 20 seconds earlier it had a descent rate of 380 m/min (1,248 ft/min), nearly twice what it should have been.

The PAPI lights for the approach (shown in Figure 1.2) signaled “below glide-path” from a point 8.3 km (4.5 nm) from the runway to “well below glide-path” at the 5.6 km (3 nm) point. Procedurally, any indication of a “too-steep” glide-path should be immediately followed with a positive correction. All crew members stated they were shocked upon hitting the ground (NTSB report, 2002). Despite the PAPI indications, none of the pilots perceived their glide-path to be below normal and had not imagined the accident that was about to occur. Figure 1.4 provides a better description of how the lights inform the pilots of their position relative to the desired 3-degree glide-path.

Figure 1.3 Black hole illusions

Source: From Gibb, 2007.

Figure 1.4 Precision approach path indicator lights

The colored lights were developed to assist pilots regarding their glide-path to the runway. Granted, each pilot may have his own perceptual interpretation of the lights and manner by which he controls the aircraft relative to the lights; regardless however, all white indicate an approach that is too steep and all red signals a flight path that is dangerously low regardless of technique or aircraft. Consequently, immediate and appropriate control inputs are needed by the pilots in these extreme situations.

To better understand the accident sequence, the description of events will begin at approximately 5:13 AM local time, about 24 minutes prior to the aircraft landing short. At that time the flight engineer, after coordinating with the airfield for their parking plans upon landing, briefed both the captain and first officer, as required by the commercial freight carrier’s procedures, that Tallahassee was a “moderate” risk for controlled flight into terrain. What follows are the voice cockpit recordings and summaries of their conversations up to the point of terrain impact taken from the 2002 NTSB report.

At 5:16 AM local time, the first officer (right seater or copilot), who was going to fly the approach and landing, thoroughly briefed the other two crew members on the approach into runway 27 and the captain concurred with the briefing details.

At 5:19 AM, the first officer, although having just briefed an approach and landing to runway 27, suggested to the captain runway 09 instead of 27, being that they were more conveniently aligned to land on runway 09. Runway 27 required a longer flight path to the far side of the airfield to get aligned for landing compared with already being somewhat aligned to land on runway 09. Their flight path was coming from the northwest and heading towards the east, thus landing runway 27 would require flying east for some time to then turn back to the west and then land heading 270 degrees. Because it was prior to sunrise with no traffic conflicts, landing to the east was more convenient given their position.

At 5:24:03 AM, the controller advised the crew to expect a visual approach into Tallahassee and to report when they had the airport in sight.

At 5:24:23 AM, the captain queried, “Runway nine … PAPI on the left side … I don’t know, you wanna try for nine?” The first officer responded, “We’re pointed in the right direction, I don’t know, like you said. Kinda long … taxiback.” The runway debate continued with the captain saying, “… the only advantage you have, landing to the west you have the … glide-slope … which you don’t have to the east.” (The decision to not land on runway 27 with the glide-slope, needless to say, was a key link in the chain of events leading to the mishap.)

At 5:26:41 AM, the captain asked, “You familiar with the airport here at Tallahassee?” to which to first officer replied, “No, I’m not.”

At 5:28 AM, the crew finally decided upon runway 09 for their landing.

At 5:30 AM, the first officer reported to the crew that he had the airport’s beacon in sight. The light he saw, however, was that of a power plant. According to the NTSB report, pilots flying in from the northwest direction often misperceive the power plant’s light to be that of the airport. The captain corrected the first officer. The crew then configured the aircraft for landing, accomplished the before-landing check, and the remaining transcript contains the pilots discussing their approach.

At approximately 5:35 AM, the landing gear was extended and the “before-landing check” was initiated.

At 5:36:20 AM, the first officer apologized for his final approach and said, “Sorry, ‘bout that … I was lining up on the paper mill or something.” At about the same time the aircraft’s ground proximity warning system sounded an alert, announcing passing through 305 m (1,000 ft) above the ground. With that warning and then in response to the first officer’s apology, the captain responded, “That’s all right, no problem.”

At 5:36:37 AM, the aircraft was 4.6 km (2.5 nautical miles) from the runway and correcting to final. The investigative analysis determined at this time the aircraft’s spatial position relative the PAPIs was three red lights and one white light. This is slightly low in regard to glide-path, or in other words, given their distance from the runway, their vertical position (altitude) was just below of the desired 3-degree glide-path.

At 5:36:40 AM, the PAPI would have showed all four lights as red. This indication is too low or well-below the desired 3-degree glide-path.

AT 5:36:43 AM, the ground proximity warning system sounded an altitude alert; the captain replied, “Stable.” The safety board determined at this time the aircraft was 152 m (500 ft) above the ground and 3.3 km (1.8 nautical miles) from the runway. Their vertical descent speed was 380 m/minute (1,248 feet per minute). The aircraft’s glide-path at this point in the visual approach was...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Contents
• List of Figures
• List of Tables
• Foreword
• 1 Vision in Aviation
• 2 Sensation and Perception Foundations
• 3 The Role of Basic Visual Functions in Aviation
• 4 Pilot Perspective of Cues Used for Visual Flying
• 5 Research on Cues Used for Visual Flying
• 6 Spatial Disorientation—Cues, Illusions and Misperceptions
• 7 Aviation Mishaps: Misperception of Visual Cues
• 8 Aviation’s Future: Technological Advancements to Visual Perception
• Index