What makes it so hard? There is first of all the fact that the modern airplane has a very shallow gliding angle and thus must approach its field along so shallow slanting a line. It is as if you had to shoot at a target, with the target not facing you but set almost edgewise to you; the slightest error would make you miss not only the bull’s eye but the whole target! (Langewiesche, 1944, p. 263)
Flying an airplane is a perceptually learned process in terms of the pilot understanding invariants for the ecological control of the aircraft (Benson, 1999; Lintern, 2000). Salient visual cues used by a pilot are above sensory threshold and provide perceptual information for accurate aircraft control. Therefore, for a visual cue to be perceptually effective, it must convey information to the pilot. If an aircraft control input is made that alters the spatial position of the aircraft, cues within the visual scene need to reflect that change. Thus, the best visual cues for a pilot to perceive are those that are sensitive to even the slightest aircraft positional change. A visual cue that does not change given gross aircraft control input is probably not an effective cue (Lintern). However, some visual cues, by remaining constant, provide information to the pilot; these are called invariants.
There are many sources of information pilots have access to regarding their aircraft’s status. Those sources of information range from throttle(s), yoke/stick, and rudders as well as the engine sound and the feel of the aircraft in terms of vibration and pull of gravitational forces. The dominant and most important perceptual cue, however, is vision (Leibowitz, 1988; Smith, 1999). Aviation is a visually-controlled behavior, hence vision’s dominance in aviation regardless of the type of flying or maneuvering. As Langewiesche (1944) stated above, visual perception is not easy. Recall in Chapter 1, Smallman and St. John (2005) coined the term naïve realism, defined as a “misplaced faith in people’s ability to extract information from realistic displays” (p. 7). The authors also explained the challenges of understanding visual perception and stated that visual perception is hard, flawed, and spartan. So it is with this challenge that this book and specifically this chapter attempt to describe the visual perceptual experiences pilots encounter.
This chapter briefly introduces the visual aspects of aviation. The intent is to enhance understanding of the operational maneuvers pilots accomplish as well as the complex environmental perception requirements needed to safely operate an aircraft. This information should help the reader better understand the visual illusions shared in Chapter 6 and the mishap descriptions presented in Chapter 7. This chapter is written from a pilot’s perspective regarding the cues that a pilot uses when flying. The following chapter, Chapter 5, addresses many of the same visual aspects of flying but from a completely different perspective. Chapter 5’s approach is not from a pilot’s perspective, but more from a vision research or human factor’s perspective of visual perception cues. Consequently, some of the terms, concepts, and studies introduced in this chapter are repeated in the following chapter but the discussion is couched in research rather than “pilot-speak” operational use.
The phrase “environmental perception” is introduced to assist the reader in its use throughout this chapter and beyond. We use environmental perception to refer to a pilot’s perception of cues from his/her aviation viewing environment, to include all prior experience, training, and expectations a pilot has of that viewed environment. Our use of environmental perception acknowledges both direct external perception of the cues perceived as well as the pilot’s cognition of those cues. This is contrasted with the strict definition of “ecological perception.” Ecological perception refers to purely direct perception of one’s environment and does not include the cognitive components. Gibson, the father of ecological perception, advocated no cognitive aspects to this form of perception; he believed that everything an observer needed to perceive in the environment was directly available within their visual scene. Gibson’s perspective takes perception to its extreme, but fails to account for prior experience, learning, expectations, and mental models an observer has when interacting with an environment. Many of the illusions and disorientations experienced by pilots are the result of a disconnect between what a pilot directly sees (sensation) and what a pilot expects to see (perception of the scene). These illusions are presented in Chapter 6.
Environmental perception of the aviation visual scene is what allows a pilot to create and maintain spatial orientation. This is contrasted with spatial orientation created and maintained via instrument flying … the use of displays to indirectly form aircraft spatial position. Because this book and specific chapter pertain to “visual flying,” environmental perception refers to the act of pilots using vision of their external visual scene to directly guide their actions, without the use of instruments.
One final term needs clarification prior to exploring visual flying cues. In the opening paragraph the concept of an “invariant” was introduced. In environmental perception an invariant is a cue that does not change within the optical array across time and can serve as a macro-level cue used for the pilot’s perception. For instance, if a pilot is flying an approach to landing and the horizon is visible, the horizon is an invariant. The horizon’s general location relative the runway does not change as the pilot descends. Another invariant during an approach to landing in terms of environmental perception is the location of the runway in the pilot’s environment, remaining relatively stable in the windscreen. This is contrasted with changing texture of the foliage beneath the pilot that increases in detail as the pilot descends toward the terrain. Therefore, some visual cues provide information to the pilot by not changing, whereas other visual cues that do change provide information to the pilot. The pilot’s perceptual challenge is determining which of many environmental cues are the most pertinent toward a safe landing or for maintaining safe altitude clearance.
The most challenging portion of learning to fly any aircraft is the approach-and-landing phase because of the small margin for error (Benson, 1999). Complicating the visual interpretation of flying an appropriate visual glide-path down to landing are the highly interdependent and dynamic actions required to maintain the desired glide-path. A glide-path is the angle to aimpoint line along which a pilot maneuvers the aircraft to landing. It is described in more detail later in this chapter. Figure 4.1 depicts a 3-degree glide-path. If flying an instrument approach to landing, this exact glide-path is displayed via aircraft instruments and navigation displays. Flying a visual glide-path to landing, without the aid of instrumentation, is more of an approximation via a pilot’s “mental picture.” This mental picture of the appropriate glide-path is practiced over and over and engrained into a pilot. The intent of the training is that a pilot will know what the appropriate visual picture to a runway looks like regardless of the surrounding environment and different runways. Bressey (1976) graphically articulated the experience a commercial airline pilot feels when flying an instrument approach to landing as one of “sliding down an electronic banister in the sky with some 200 tons of aircraft strapped to his posterior while the ground is coming up to meet him at an approximate speed of 230 ft per second” (p. 16).
Figure 4.1 Altitude and distance of a 3-degree glide-path
Figure 4.1 demonstrates that to maintain the appropriate 3 degree glide-path at certain distances from the runway the aircraft must be at a particular height above the ground. This perceptual task requires constant updating of one’s distance from the runway and altitude above the ground (surface plane of the runway). This task, however, is prone to many perceptual errors and these errors are presented in detail in Chapter 6. For example, perception of runway shape and size based on previous training and experience make a pilot prone to perceptual constancy problems, also addressed in Chapter 6.
There are as many techniques available to use during an approach to landing as there are the number of instructor pilots teaching people how to fly (Pitts, 1967). Hodgson detailed the basic information a pilot must have for a visual approach to landing: (1) pitch and roll attitude information, (2) horizontal and vertical velocity information, (3) position information relative to the desired landing runway, and (4) vertical flight path information in terms of distance from landing point, height above touchdown point, and height above terrain (1971, p. 205). Hasbrook (1971) described the necessary control of certain variables for a safe and successful landing. He listed aircraft vertical and horizontal speed as well as heading. Hasbrook stressed speed control because it incorporates pitch angle and thrust setting dynamics. He also mentioned runway size and shape as cues for a pilot conducting a visual approach to landing.
Bressy (1976) in his description of a visual approach to landing stressed two reference planes a pilot must monitor: a vertical plane through the center of the runway and a glide-path. A pilot must continuously monitor the intersection and displacement of the two planes, as well as heading and rate of closure and rate of change of heading relative to each plane. Bressy acknowledged that it is easy to monitor heading relative to the runway, but the displacement above or below glide-path is difficult because it results in extension or compression (termed foreshortening) of the runway picture from the desired glide-path.
A visual approach to a runway can be flown either via a straight-in approach or from an overhead, depicted in Figure 4.2. A visual straight-in approach normally occurs from a distance of 9.3 km (5 nm) directly lined-up with the intended runway. Visibility conditions usually dictate when the visual straight-in formally begins, which in good weather, clear visibility, and appropriate terrain could be 10 miles from the runway. In contrast, a visual overhead pattern and landing is a descending turn to position the aircraft 2.4–0.8 km (1.5 to 0. 5 miles) on final. Imagine a 180-degree turning and descending merge lane on a freeway—this is what the overhead final turn is similar to. The term “final” refers to the last phase of the approach to landing common to both the straight-in and overhead pattern. If a plane is on final, it is nearing the final portion of the approach, almost to the runway. This is contrasted with the final approach fix, the latest point in space at which a pilot would normally configure the aircraft with gear and flaps. This final approach fix is normally associated with an instrument approach and is comparable to a 9.3 km (5 mile) point on a visual approach. Often it is at this point that the aircraft no longer maintains level altitude and begins the descent to the landing runway on the straight-in.
Figure 4.2 Visual overhead and visual straight-in approach depictions
The straight-in visual approach and landing is broken down into six parts: (1) runway 2) airspeed and power, (3) horizon, (4) glide-path, (5) aimpoint, and (6) field of view references. In the following chapter, the approach to landing is only discussed in terms of runway alignment, glide-path control, and the actual landing phase referred to as the “flare.” Because this chapter presents a pilot’s perspective of visual flying maneuvers, for completeness the six aspects of an approach and landing are detailed. Figures 4.3 to 4.10 depict photographs of final approach to landings in a variety of locations representing terrain differences, distances to the runway, weather conditions, and day/night conditions. As the discussion continues on the six aspects of a landing, reference to the photographs in those figures will aid in the description.
The starting point for a visual straight-in for landing begins with runway alignment. The aircraft vector is controlled directly toward the intended runway. In no-wind conditions this equates to pointing the nose of the aircraft at the runway. A crosswind, however, may require the pilot to “crab into the wind,” so that the nose may not point at the runway (it points into the wind), but the direction of flight (vector) is still towards the runway.
Figure 4.3 Three photographs of an approach to landing
Source: With permission from Steven Kaplan photographer, http://www.airliners.net/photo/Ansett-Australia-Airlines/Airbus-A320-211/0084956/&sid=8947f6d638361fe73446e8bd6 a1a2980.
Riordan (1974) surveyed 360 commercial airline pilots and found the pilots rated the runway image and shape/size as their most used visual reference for an approach to landing. The concept of runway alignment is the easiest for inexperienced pilots to grasp as the runway also serves as the aimpoint. Initially it is a distant, non-descript visual cue, but as the pilot closes the distance, the runway systematically increases in size and detail, allowing for more specific aimpoint targeting. Figures 4.3 to 4.10 all depict very unique landing environments that pilots must correctly interpret for a successful landing. Figure 4.3 includes three photographs depicting a plane as it approaches the runway; note the change in the shape/size of the runway as the pilot gets closer.
Related to the runway is the concept of splay, described as the angle from a line perpendicular to the horizon. For a given runway, splay increases as altitude decreases and decreases as altitude increases. Only for extreme departures from desired glide-path at close distances to the runway will splay be a salient visual cue for landing (Lintern, 2000). A more effective way to understand splay is to consider the size and shape of the runway. If a pilot is shallow or low while on approach, the runway will appear short and wide, with the front of the runway very wide relative to the far end. This is how the runway appears in the third photograph in Figure 4.3. Splay also can be described in terms of linear perspective because the runway may appear to emanate from a distant point near the horizon. In contrast, if a pilot is high on glide-path, well above the runway, or simply farther out from the runway, it will appear more orthogonal, thinner with the near and far end more equal in width, that is, less splay. The photograph, Figure 4.3, showing the view furthest from the runway illustrates an image of the runway that is more orthogonal. This concept of splay is discussed in Chapter 5 from a more visual perception research perspective.
The size of the runway may also influence perception of runway distance. This idea will be discussed again later in Chapter 6 but is worthy of introduction here as well. For instance, Figure 4.4 depicts a runway that is long and relatively thin, with a length-to-width ratio of 91 (13,793 × 150 ft). Runways with high ratios appear more orthogonal and have less splay than runways that have smaller ratios. High ratio runways may be interpreted as being farther away than runways with low ratios. As is more completely described in Chapter 6, the interpretation of runway ratio will be affected by a pilot’s previous experiences with runways of other ratios, and the pilot’s interpretation can influence his choice of glide-path.
One last point needs mentioning regarding the runway. As stated above, pilots use the runway as their intended target or aimpoint (the visual goal); however, most pilots fail to appreciate visual cues other than the runway itself. The runway serves as the egocentric objective, but the surrounding terrain provides global environmental perspective. It is the environmental orientation via ambient vision that allows for accurate, visually controlled actions to safely and successfully land an aircraft.
Figure 4.4 Landing at Albuquerque International Airport
Source: With permission from Dan Jordan, photographer, Airliners.net, from http://www.airliners.net/photo/-/-/1010744/.
Flying a straight-in approach requires the pilot to maintain a constant airspeed, which varies greatly depending upon type of aircraft, type of flap setting, and aircraft weight/fuel load (approach speed is a function of stall speed). Appropriate throttle settings, thrust, for a given aircraft-configuration greatly stabilize the airspeed control. But even having the correct power setting does not always result in a good approach. For instance, nose-low attitudes may result in an increase in airspeed unrelated to power setting, just as an increase in pitch attitude, nose up, will slowly deplete the airspeed. Also, adding or reducing power may not only increase/decrease airspeed but may impact glide-path. A common mantra in flying an approach and landing is “aimpoint, airspeed.” Consequently, maintaining proper airspeed is an important aspect for an approach and landing (Hasbrook, 1971).
The horizon serves multiple purposes for a pilot during an approach to landing. For the most part, it is not appreciated by a pilot as his/her gaze is fixated upon the runway and the intended spot of landing, (i.e., the aimpoint); however, the horizon provides essential ambient and global environmental feedback to the pilot regarding wings-level status as well as pitch information without having to reference the attitude indicator. Thus, while focal vision is consciously focused on the aimpoint, the horizon provides feedback to pilots regarding their orientation relative to an earth-fixed reference. When the horizon is absent (as in Figures 4.5 and 4.8), the pilot must rely on his/her attitude indicator to ensure proper pitch and bank are maintained during an approach.
The horizon may either be explicitly or implicitly defined for use by a pilot. Figures 4.3 and 4.4 have well-defined, explicit horizons. Thus, a pilot has a world-sized attitude indicator that lacks no ambiguity. But sometimes meteorological conditions do not allow for an explicit horizon and the implicit horizon is all that is available. An implicit horizon is simply one that is not clearly defined. Figure 4.8 with the fog in the Azores does not provide reliable cues for the horizon’s location. However, there are times on a clear night when the horizon can easily be seen given moon illumination and the appropriate cultural lighting and terrain features.
From a pilot’s perspective, the horizon is also used for establishing a gap, which is a distance of sky versus ground within the field of view of the pilot (Lintern and Liu, 1991; Benson, 1999). Later discussion presents the horizon as a visual invariant for horizon-angle (or H-angle), an angle generated between horizon and aimpoint. For a normal landing within the pilot’s field of view, the horizon perspective is half ground and half sky. Thus, the horizon is the dividing line. The horizon also helps establish the runway surface plane for ground orientation. Langewiesche (1944) described the horizon as an invariant for landing because the horizon never moves relative to eye-level.
The horizon also plays a role during the landing flare. The “flare” is when the pilot is just about to land and thus decreases the aircraft’s speed and sink rate to allow for a smooth touchdown onto the runway. A technique in landing an airplane involves looking to the horizon during the flare to help gauge height above the ground. This also helps avoid ground-rush, the “optically violent” global optic flow rate (Warren, 1988, p. A121) that occurs when looking directly at the ground while traveling at a high speed in the downward vertical vector. As the pilot looks towards the horizon during the landing flare, peripheral vision “picks-up” external cues to the side of the airplane that provide “sink-rate” information. This environmental perception is accomplished by ambient vision, which is physiologically able to detect movement and rate of change of movement. These environmental ambient cues along the Hudson River may have made the safe water landing possible for Captain Sullenberger. Landing at night or in impoverished visual conditions, however, often produces less smooth landings because of the limited ambient vision cues.
The biggest challenge in accomplishing a straight-in approach and landing is maintaining a stabilized glide-path to the runway. The normal glide-path is 3 degrees. There are variations ranging from 2.5 degrees to 4 degrees, but 3 degrees is the standard (see Figure 4.1). In Figure 4.1, note the glide-path arrow points at a spot just a bit past the beginning of the runway; this is the aimpoint. This spot is normally 152–305 m (500 to 1,000 ft) down the runway, although some airplanes do aim for “brick-one” of the runway, (i.e., the very beginning), but this is the exception. A pilot may aim at the beginning of the runway if the braking ability of the aircraft is in question or the surface condition of the runway may prohibit stopping within the available runway length (e.g., wet, snow, ice). By aiming just past the beginning of the runway the pilot allows for a margin of error in case they do land shorter than their desired aimpoint. A pilot does not want to aim too far beyond brick-one and subsequently land too far down the runway either, for a pilot never knows when they may have needed an extra 152 m to ensure being able to stop on the runway as opposed to departing a prepared surface and running off the end of the runway.
Glide-path control involves keeping the aircraft’s vertical velocity within desired range given the target airspeed. For an approach speed of 232 km/h (125 knots), a vertical velocity of 203 m/minute (665 feet/minute) descent maintains a 3 degree glide-path to the runway. The logic behind the glide-path is that if it is too low (less than 2.5 degrees), it brings the aircraft dangerously close to possible terrain hazards. Too steep a glide-path (greater than 3.5 to 4.0 degrees) brings the aircraft onto the runway at high rates of descent that present three problems. One, higher rates of descent result in harder landings. Consequently, structural fatigue problems may occur with the aircraft because the landing gear is absorbing excessive forces upon landing. Second, pilot and passenger comfort come into play with hard landings. Finally, steep approaches involve low throttle settings. To maintain airspeed in a steep descent requires retarding throttles possibly to idle. This becomes unsafe in the event of a go-around or missed approach; the aircraft is in an unsafe position to land and the pilot must immediately increase power to gain enough thrust to change the aircraft’s vector, up and away from the runway. Therefore, the 3-degree approach is the right mix of obstacle clearance towards the runway, smooth vertical descent for transition to a comfortable and safe landing, and shallow enough to require the pilot to carry power toward the runway in the event that a go-around (an aborted landing) is necessary.
Maintaining glide-path involves a perceptual learning process of a “mental picture” of the appropriate angle of descent towards the runway. Mertens (1979) described it when a pilot’s visual scene looks “correct” based on appropriate runway slant, size, and shape. Much of flying an approach and landing is based on direct perception; however, as mentioned at the beginning of this chapter, the cognitive aspect of prior experience is also involved in any visually-guided action (Haber, 1981). Figure 4.5 portrays time-elapsed photography of an aircraft landing at Madeira Airport, Azores, Portugal. This photograph depicts the glide-path the pilots took as they guided their aircraft toward the runway using a combination of approach instrumentation as well as stored knowledge of the appropriate visual picture of a 3-degree glide-path to landing. Additionally, Figure 4.3 and its series of three photographs show from the cockpit view the glide-path flown toward landing—the mental picture guiding a pilot’s visually controlled actions. The scene in Figure 4.6 may challenge pilots to maintain their glide-path because of the close proximity of final approach to the hill and houses on the pilot’s left. And finally, Figure 4.9, the landing in Estonia, shows the pilot “on glide-path” with the two white lights on the left and the 2 red lights on the right as depicted by the VASIs (visual approach slope indicator lights). The visual mental picture is reinforced with the VASIs confirming the visual cues.
Figure 4.5 Night time-lapsed photograph at Funchal, Portugal in the Azores
Source: With permission from Rui Sousa, photographer, Airliners.net, http://www.airliners.net/photo/TAP-Air-Portugal/Airbus…/0646366/M/.
The proper mental glide-path picture must be fairly robust to overcome countless changes in the runway environment, surrounding terrain differences, and varying levels of visibility as pilots attempt to maintain “the picture.” At greater distances to the runway a pilot is able to safely make some extreme deviations above or below glide-path to determine what the proper glide-path is given a particular runway. The first author has done this numerous times at unfamiliar locations in an attempt to determine just where the current visual scene relates to a stored mental model of the “visual picture” from memory. For instance, if unsure of the glide-path, a pilot can alter his/her altitude to go above and below until it “looks right” given the distance from the runway and the altitude above the ground. This maneuver by a pilot on a visual approach is a good example of environmental perception. Galanis, Jennings, and Beckett (2001) discussed this idea of a build-up or lag in glide-path correction whereas Lintern and Koonce (1991) called this a build-up of “visual evidence” (p. 69).
Thus far the primary discussion of risk involved with landing an airplane has centered on impacting the terrain prior to the runway. When a perfectly worthy aircraft unintentionally impacts the ground it is called “controlled flight into terrain -- CFIT.” It is fitting within the discussion of glide-path to discuss poor glide-path maintenance and too steep of an approach. The consequences of being too steep on approach are not as severe unless the landing runway is unusually short. If steep on an approach the pilot has a few options:
Figure 4.6 Landing at Matre Airport, Sao Paulo, Brazil
Source: With permission from Stephan Klos Pugatch, photographer, airliners.net, http://www.airliners.net/photo/Blue-Air-Taxi/Embraer-EMB-810C-Seneca/1413563/M/.
1. Accomplish an aggressive descent and re-establish the desired glide-path to the original aimpoint. It is difficult to intercept the glide-path from above if there is limited distance to the runway. Normally a pilot does not want to have an excessive vertical descent rate toward the ground with limited altitude, which is the case if trying to re-establish glide-path prior to the runway.
2. Accept the current glide-path and simply establish a new aimpoint further down the runway. This is probably the safest option if the runway is long enough to still allow normal braking action and stopping within the given runway length.
3. If the runway is short, accept the steep glide-path angle to the current aimpoint and prepare for a faster and harder (less flare) landing.
In this short runway case, which is the most dangerous, if the aimpoint is shifted down the runway the pilot is landing well beyond usable landing surface and greatly increases the chance of running out of runway prior to stopping the aircraft. If the runway is wet or the braking of the aircraft is less than optimal this could result in departing the prepared surface of the runway.
The discussion above went into detail to clearly present to the reader that being steep on approach is a dangerous place to find oneself. Impacting the terrain is not the main concern if a visual illusion induces a pilot to fly higher and away from the ground; however, it has its own dangers in that there are hazards while attempting to land. An accident that demonstrates this relates to Figure 4.5, Madeira Airport. In 1977 an aircraft attempting to land in a heavy storm landed too far down the runway, failing to stop due to the wet runway and high speed in the available runway remaining. The runway at the time was only 1,600 m (5,250 ft). Two construction projects, one in the 1980s and one in 2000, extended the runway to what it is today, 2,781 m (9,124 ft) making it much safer for large aircraft to take off and land.
According to Pitts (1967) the judgment of height is the most important perceptual skill for a pilot. This concept of height estimation, vertical awareness, plays a crucial role in glide-path maintenance to determine rate of change of height perception. Known pitch and power settings ensure the aircraft is at the appropriate height given the distance to the runway for ideal conditions but even those parameters change as a result of aircraft weight and winds from one approach to the next.
The aimpoint cue refers back to the first half of the “aimpoint, airspeed” mantra and is closely related to glide-path, as the angle to aimpoint is simply the desired glide-path. Once a pilot starts down glide-path, shown at the “final approach fix” in Figure 4.1, a common practice is to put the runway in the center of the windscreen (Figures 4.6, 4.8, and 4.9). The runway then becomes a perceptual invariant, a source of visual information that should not change while flying the approach. This “gun-sight” technique is questioned, however, by some (e.g., Hasbrook, 1971; Mertens, 1979) because turbulence and head movements may appear small and insignificant but could result in excessive glide-path deviations. This common technique, which must be continuously monitored, is one of many visual cues to establish glide-path towards the appropriate spot on the runway.
As the aircraft gets closer to landing the pilot can see more detail in the runway environmental cues. This availability of detail signals the point in time when the pilot picks a spot on the runway as their specific aimpoint. Often the chosen aimpoint is 152 m (500 ft) or 304 m (1,000 ft) down from the beginning of the runway (from “brick-one”). It must be stressed this is the aimpoint, not the eventual landing point. The aimpoint is a spot on the runway that the pilot directs the aircraft down towards the runway until 15 and 2 meters (50 and 6 ft) above the surface. At that time, the pilot initiates the “flare” by completely reducing power to idle (if not already) and breaking the descent rate to smoothly touch down on the runway surface. Depending upon the aircraft, this could be a reduction of 15.8 km/h (10 knots) and cutting the 183 m/minute (600 ft/minute) descent in half to 91 m/minute (300 ft/minute). The aimpoint shift results in a landing 152–304 m down the runway beyond the aimpoint, thus landing the aircraft 610 m (2,000 ft) down the runway beyond the threshold. Due to the pitch of the aircraft and the limited downward viewing angle of a pilot out the windscreen, the aimpoint and touchdown landing point are not actually viewed by the pilot in the last phases of the approach and landing. This would only be possible if the airplane had a glass bottom for the pilot to see through, similar to some commercial helicopters.
Figure 4.7 Final approach to landing at Great Barrier Reef Airport, Hamilton Island, Australia
Source: With permission from Darren Howie, photographer, airliners.net, http://www.airliners.net/photo/-/-/0978838/L/.
Figure 4.8 Short final for landing at Sao Jorge, Portugal in the Azores
Source: With permission from Joao Resendes, photographer, www.positiveclimb.com and airliners.net, from http://www.airliners.net/photo/SATA-Air-Acores/British-Aerospace-ATP/0596916.
Figure 4.9 Landing at Tallinn Airport, Estonia
Source: With permission from T. Phelps.
Another aspect of glide-path and aimpoint is pitch control. Pitch is the vertical movement of the aircraft’s nose. Pitch is related to power and airspeed in that, for a given throttle setting, too low of a pitch will greatly increase airspeed and too high of a pitch will decrease airspeed and neither condition is acceptable for a stabilized 3-degree visual glide-path. Pitch control is how a pilot directs the aircraft towards the aimpoint. Improper pitch in the nose down direction will cause the aimpoint to move up in the windscreen from its center position, giving visual feedback to the pilot regarding an aimpoint short of intended landing. Pitch up of the aircraft in turn may cause the aimpoint to move down from center in the windscreen, resulting in the aimpoint further down the runway.
The aimpoint is important to maintain throughout the approach. Often an aircraft may deviate slightly from desired 3-degree glide-path, and the pilot may elect to reestablish the 3-degree glide-path. This must be done relative to the original aimpoint. To correctly accomplish glide-path correction, a pilot must momentarily fly either more steeply or more shallow to re-establish the 3-degree glide-path for the same, consistent aimpoint. For example, if a pilot deviates from the 3-degree glide-path and lowers the nose, thereby increasing pitch in the down direction, the aimpoint will move up in his/her windscreen and if continued on this path, the vector would put the aircraft to land short of the runway (flying well below the desired glide-path). To correct this, the pilot must raise the nose of the aircraft, pitch up, and fly shallow-to-level momentarily until a re-established 3-degree glide-path is intercepted for the original aimpoint, as shown in the time-lapsed photograph of Figure 4.5.
The ideal pitch control is to maintain the aimpoint in the center of the windscreen aligned with the center of the runway. As the aircraft gets closer to the runway, the detail of the aimpoint can be seen and the aimpoint “fills the windscreen.” It is at that time (15–3 m above the runway), the pilot shifts the aimpoint to transition to the flare and landing. This interdependence of pitch and power for glide-path control towards an aimpoint is what makes this a challenging maneuver to learn. The expansion of the aimpoint is the concept of “focus of expansion” and the flow of the optic array from the center point of “ego-motion” (Gibson, 1950; Gibson, 1979; Gibson, Olum, and Rosenblatt, 1955; Hasbrook, 1971). As a visual cue, the expansion of the aimpoint occurs just prior to landing as previously described, therefore it is not used during the majority of the approach. The flare is discussed in more detail in the following chapter in terms of visual perception research.
A paved runway is not a requisite to maintain an aimpoint as pilots land successfully on open fields or snow/ice, as shown in Figure 4.10. This ability demonstrates the importance of an aimpoint and landing surface—rather than the runway as a constructed man-made object. If landing on an open field, there are normally some effective environmental cues to assist in height and distance estimation. The change of texture and color between fields can help define where the “runway” begins; possibly a row of trees can serve as a point to attempt to land abeam (an aimpoint). These types of environmental cues are similar to those that allowed the pilot of Flight 1549 presented in Chapter 1 to safely “land” upon the Hudson River. One advantage the pilot had in that case was an extremely long “runway” in terms of the river not constraining the aimpoint and touchdown point. Thus, even without an actual runway (the preferred and most used visual cue according to Riordan’s 1974 research), ample visual cues were available to perceive height and distance. Figure 4.10, however, shows a runway carved out of snow, and the entire area is featureless for the most part; it is an axample of an extremely challenging environment for purely visual height and distance estimation.
Figure 4.10 Short final for landing at McMurdo Station, Antarctica
Source: With permission from T. Phelps.
It has been explained that pilots use pitch control to maintain the runway and aimpoint in the center of their windscreen (Benson, 1999). The windscreen is part of the pilot’s field-of-view reference for aimpoint stability. Other parts of the aircraft used are the glare-shield and canopy bow or top of the windscreen. These field-of-view references can be used in reference to the horizon. The horizon may be in the top third of the windscreen and become an invariant for glide-path control. The gap or distance between the glare-shield and the aimpoint provides feedback regarding stability of the glide-path. Field of view references are depicted in Figures 4.3, 4.6, 4.8, and 4.9 in terms of where the runway and aimpoint fall relative to the pilot’s out-the-window perspective.
The overhead pattern is a much shortened version of the straight-in approach, but has similar characteristics. The runway serves as the primary visual reference throughout the overhead pattern. The final 2.4–0.8 km (1.5 to 0.5 mile) portion is the same; however, to get to that point, the pilot must maneuver the aircraft in a 180-degree descending turn (shown in Figure 4.2). It is much more difficult than a straight-in because the pilot must visually control the aircraft’s bank to guide the changing heading as well as deal with the previously mentioned aspects of runway variables. As mentioned earlier in the chapter, the overhead pattern requires the pilot to maneuver the aircraft around the final turn; analogous to a 180 degree downhill merge lane of a freeway. The two most challenging aspects of the overhead pattern are runway displacement upon roll-out for lateral control and intercepting the desired glide-path for vertical control. This second challenge combines rolling out on final with the proper vertical displacement given the horizontal displacement … equating to the appropriate glide-path.
Another aspect of the final turn to landing is that the pilot must account for wind in terms spacing from the runway, vertical descent during the final turn, rolling out on final, and how to position the aircraft to counter any drift due to winds; the aircraft’s vector must continually point toward the aimpoint. Environmental perception also includes clues that inform the pilot of wind direction and how that wind directly influences the control inputs used by the pilot to fly the aircraft to final.
Beall and Loomis (1997) investigated optic flow and visual analysis of the base-to-final turn in their research. They colorfully suggested how pilots accomplish such a maneuver: “the pilot perceives the 3D spatial layout of the terrain (including the runway), perceives the 3D motion of the aircraft prior to the turn, and then plans the turn through some process tantamount to solving differential equations” (p. 206). Their description was a bit tongue-in-cheek as they doubted this process was required for pilots and instead offered a theory consisting of optic flow variables and splay rates. Beall and Loomis had pilots fly the same approaches at both night and day and explored the role of ground texture on pilot’s performance. They hypothesized that performance would not be different between day and night and that is what they found. They attributed performance to the pilots’ perceptual assessment of the runway’s splay as they turned to final.
Beall and Loomis’ (1997) finding suggests that in calm winds at a standard altitude for an overhead pattern, 305–457 m (1,000–1,500 ft), minimal visual perception is needed to get close (i.e., complete the final turn). Thus, experienced pilots who know the pitch and power settings as well as bank angle are able to fly the maneuver with minimal environmental cues. For instance, the first author’s experience in five different but similar aircraft had approximately the same parameters: 30 degrees of bank and a pitch setting of 2/3 ground and 1/3 sky. Beall and Loomis’ (1997) research is again examined in Chapter 5 and expands the discussion in terms of visual perception of splay.
The idea of established parameters or criteria, known as “windows of acceptable performance” for pilots to continue their approach to landing is a lesson often learned the hard way in aviation circles. According to Turner (2007), a stabilized approach is the key to workload management and a good approach leads to a good/safe landing. Unfortunately, many pilots have the wrong mindset while flying, and that is to “salvage an approach” no matter how unsafe because “pilots are overwhelmingly optimistic and the culture of aviation places great value on innovating to recover from nearly hopeless situations … the result is a mindset that we can salvage any situation, no matter how bad” (p. 2). Far too often pilots have continued approaches despite airspeed, vertical velocity, and vertical/lateral approach limits being out of acceptable safety margins. Commercial aviation was the first truly to embrace the use of parameters to help with the decision either to continue the approach or execute a go-around/missed approach.
When evaluating the criteria, it is important to remember that all of the aspects of an approach to landing are interrelated. The current section on visual approaches began by stating flying and maintaining precise parameters were very challenging because of the highly interdependent and dynamic factors involved. It is due to this interaction between airspeed, pitch, power, glide-path, and aimpoint that the correction of one directly influences other parameters and may lead to unstabilized approaches. The following is a scenario often encountered by pilots.
A pilot determines that the aircraft is above the desired 3-degree visual glide-path. To correct the glide-path the pilot reduces power and pushes forward on the controls to lower the nose (and momentarily moving the aimpoint extremely short of the runway). Also during this correction, the vertical velocity increases due to the descent. Then upon re-intercepting the glide-path the pilot brings the nose of the aircraft back up and establishes the original aimpoint. While correcting the glide-path, however, the pilot fails to re-establish the proper power setting (having left it reduced to account for the original descent) and now with the power too low, the airspeed of the aircraft decelerates. To correct the slow airspeed, the pilot pushes the power up and accelerates. But this also has the inadvertent effect of generating thrust and subsequent lift. And although the aircraft’s speed is no longer an issue and the descent rate reduced, the pilot has shifted the aimpoint down the runway, and is now climbing above the desired 3-degree glide-path.
This scenario has happened to all pilots when they were learning how to fly and may have also happened during a task-saturating approach if juggling other distracting tasks, such as an emergency procedure. The above example described an unstabilized approach … the pilot failed to maintain aircraft parameters within expectable limits. Experienced pilots know that accurate and precise flying requires numerous micro-corrections. Pilots need to avoid over-correcting or becoming impatient by making large corrections.
Khatwa and Helmreich (1998–9) produced an impressive report for the Flight Safety Foundation on controlled flight into terrain. Recall, this is when an airworthy aircraft unintentionally impacts terrain. One of their recommendations specifically addressed stabilized approach criteria as a change for standard operating procedures to minimize the risk of controlled flight into terrain. A “no fault go-around policy” would also encourage pilots to cognitively prepare themselves to “go missed approach” and not worry about any employment repercussions. The primary changes advocated by the authors were (p. 52):
1. Acceptable stabilized-approach criteria that would require necessary visual cues to continue descent below MDA/DH (minimum descent altitude/decision-height) as well as flight deck alerts (e.g., GPWS [ground proximity warning system]) requiring timely action.
2. An approach-ban policy that prohibits the continuation of an approach beyond a point not less than 1,000 ft [305 m] above the threshold of the landing runway, unless minimum visibility or runway visual range requirements as appropriate for that particular approach type are met or exceeded.
Turner (2007) in an Aviation Safety magazine article presented industry accepted norms for stabilized approach criteria, listing specific criteria for both instrument and visual approaches. Basically a pilot is to execute an immediate missed-approach or go-around if deviations are observed in terms of (1) more than 3/4 scale lateral deflection on Course Deviation Indicator if instrument or not aligned with the landing runway if visual, (2) airspeed: 5 knots slow or 10 knots fast, (3) rate of descent exceeds 1,000 ft/minute, and/or (4) pitch is lower than 10 degrees below or 5 degrees above horizon.
The point of a stabilized approach is that pitch, power, and attitude parameters are met and minimal changes are made to the aircraft to allow for the safest possible approach to landing. Given the aircraft’s configuration, it is of the utmost importance to have the aircraft properly trimmed (aerodynamic controls pressures are equaled out) and power set. In many ways a stabilized approach is similar to aerial refueling, which is very common in military aviation. Figure 4.11 depicts aerial refueling. Attempting to rejoin (two or more aircraft coming together during flight) on a tanker aircraft is exceptionally difficult due to the lack of ambient visual cues as one approaches another aircraft. To make it manageable the airspeed of the tanker needs to be known to the adjoining aircraft and known visual cues of the tanker’s aircraft can provide approximate distance information. For instance, if certain details on the tanker’s aircraft can be seen, these visual cues provide feedback to the approaching pilot regarding the distance from the tanker aircraft. Also, calculated distance information between the two aircraft is available (using internal specific identification codes) and is necessary to confirm distance as well as the known overtake speed relative to the tanker. The visual cues are not reliable enough on their own. Also, a purely visual rejoin is very difficult and often results in a stagnant rejoin (not generating any overtake due to fear of too much speed) or an overshoot because of too much overtake speed.
Figure 4.11 Aerial refueling photograph
Source: With permission from T. Phelps.
This refueling example depicts the difficulty in visually-guided actions and perceiving environmental cues. Attempting to gracefully contact a tanker aircraft when it is the only object in the sky is as perceptually challenging as trying to gracefully land on a runway when it is the only object on a dark night. The key to success in any landing environment is a stabilized approach to ensure a safe landing. Given impoverished visual conditions, a stabilized approach will reduce cognitive workload requirements and allow a pilot to better focus on other factors and not be saturated with erratic aircraft control inputs. According to Turner (2007), unstabilized approaches are correlated with approach-and-landing accidents. Correlation is not equated with causation; however, a predictive relationship exists that must be respected by pilots.
According to Captain Tarnowski, an Airbus test pilot, “stabilized, constant descent angle final approaches significantly raise the safety level of this flight phase” (2007, p. 21). Tarnowski suggested that pilots can fly every approach similar to a precision approach using stabilized approach criteria with the help of cockpit technology—eliminating the unstabilized manner in which non-precision approaches had been flown in the past.
In order to better understand much of the discussion in this book, reference is often made to a pilot accomplishing a go-around or missed approach. This maneuver occurs when a pilot makes the decision to not land and immediately increases power and pitches the aircraft up to climb away from the ground or runway. The reason to initiate a go-around is primarily due to safety of flight. Many different situations may cause safety of flight concerns: a pilot not in a safe position to land, being either too high or too low relative to the runway; a pilot with excessive airspeed on final or approaching a stall (airspeed too low); a pilot seeing another aircraft or vehicle on the landing runway; or possibly, the pilot loses sight of the runway due to environmental conditions such as fog.
Pilots must have a sufficient amount of self-confidence to fly. This self-confidence, however, may prevent pilots from admitting that the aircraft is in a situation that may be beyond their capability to safely recover. The aviation community has come a long way in terms of improving cockpit decision-making. Many pilots, however, have successfully “salvaged” an approach (found a way to not have to go-around and landed the airplane). This history of success, combined with ego-driven decisions, makes it difficult for some pilots to “admit defeat” and perform the go-around—it may be seen as a sign of an inferior pilot. Of course, that is not the case; environmental conditions may arise that make a safe approach near impossible. Windshear conditions, visibility limitations, or runway hazards often make go-arounds a simple decision.
In summary, the runway, airspeed and power, horizon, aimpoint, and field of view references are used to maintain glide-path during the approach and landing. The paradox is that the visual approach-and-landing cues taught and used by pilots are those that are consciously accessed and described (runway size, shape, and perspective) but in actuality they may not always serve as the most useful. In reality, the ambient cues may provide the most functionally invariant sources of information and they are processed with little cognitive effort. Thus, the runway environment, the terrain, the surrounding man-made or natural features that define the location, orientation, and position of the runway within the airport’s environment are not specifically instructed landing cues, but they may prove to be the most important.
Low level flying is a thrilling but unforgiving aviation activity. The element of risk is greatly increased due to the close proximity to the ground and other hazards (birds, obstacles, other aircraft) that exist within the low-level environment. In low level flying the focus of expansion is the point on the terrain where a pilot does not want to collide. While maneuvering, the expansion point communicates to the pilot the possible point of terrain impact if the pilot fails to make a correction. This simple, yet valuable piece of information regarding the low altitude is taught to young and experienced pilots alike.
Haber and Haber (2003) described military low-altitude flight as a type of flying that, “comprises a constellation of tasks that represent the very edge of human perceptual and attentional capabilities” (p. 21). Flach and Warren (1995) described low-altitude flight as, “the unforgiving character of the dynamic ecology that imparts an element of ever present, if not always clear, danger to each moment of action or inaction and makes prescience desirable” (p. 66). Throughout this chapter and others, the topic of low-level or low-altitude flight is alluded to in demonstrating visual-perceptual limitations.
Compared with higher-altitude flight, flying low to the ground requires the additional task of terrain clearance. Regardless of the current crew activity internal to the cockpit and stimuli external to the aircraft, the number one priority must be vertical awareness with the terrain, not only at the present, but along a future vector. The future aspect of vertical awareness involves the aircraft’s flight path if left unaltered. If pilots are distracted and momentarily drop vertical awareness from their cross-check, where will the aircraft be? This is a question the pilot must continuously assess and answer. The mental-processing capacity metaphor that is commonly used in aviation is a “bucket.” Only so many tasks can be accomplished and/or handled before the pilot’s bucket becomes full. Once full, something is not going to be accomplished or handled properly. The aviation bucket of cognition, or conscious working memory, directly relates to the pilot’s ability to juggle the limited resources of attention.
Haber and Haber (2003) shared the term “time to die” in their writing and described it in terms of particular flight maneuvers and the resultant time remaining, if no action is taken, prior to ground impact. This is an operational aviation phrase, (i.e., pilot term), that certainly doesn’t hold back the consequence of failing to act. It is driven by G-forces, altitude above the terrain, and velocity vector (speed and flight path). For instance, if a pilot enters a level 5-G turn at 30 m (100 ft) above the ground, the pilot can maintain a level turn at those parameters if a bank angle of 75 degrees is maintained; however, if the pilot overbanks by 5 degrees (to 80 degrees of bank) the nose will slice toward the ground if the G is not increased. In this case, the time to die is 3.7 seconds. According to the experts in the flying unit, 2.5 seconds is provided for pilot reaction time (Haber and Haber). Consequently, 1.2 seconds is available for the pilot to sense the problem … if not perceived within that time frame, ground impact is unavoidable.
Low-level turn accidents are deadly. Due to the minimal time to react, pilots rarely have the time to eject. It has been reported that turning maneuvers only encompasses 1 percent of a US Air Force pilots’ mission time while flying low levels, but unfortunately account for 6 percent of Class A mishaps and they are fatal every time (Lyons, Gillingham, Thomae, and Albery, 1990). The cause of low-level turn mishaps can be due to many factors, such as cognitive-task saturation resulting from mission-oriented tasks competing with aircraft-control tasks. Lyons et al. stated that these types of accidents come down to two major factors: one, the physics and aerodynamics of high-speed low-altitude flight; and two, the “frailty of our orientation senses which predisposes us to develop undetected overbanks and descent rates” (p. 3). In other words, aviation provides sensation and perception dilemmas with which our body is unable to accurately cope.
Another dangerous aspect of low-level flying is ridge crossings. While flying low, often a pilot needs to maneuver over and around a ridgeline or some higher obstacle. The problem with flying too high over the ridgeline or obstacle is that the aircraft may momentarily be exposed to an enemy or, sometimes—and just as dangerously—it may fly into instrument-required weather conditions. Consequently, aggressive maneuvering is required. This aggressive maneuvering momentarily places the aircraft’s vector below the horizon, toward the ground. Thus, in terms of global optic flow, the point of expansion is a point on the ground. Recall that aviation is a visually guided behavior in which impact on the runway is desired while impact with other terrain spots is a tragic accident. Thus, pilots fly a thin line in terms of hitting what they want to hit—the runway—and not hitting what they want to avoid—the terrain.
Especially when flying low, any misperception or any delay in aircraft-control input results in minimal if not unavoidable time to die. Following an examination of one of the low-altitude accidents, Haber (1987) created a list of five characteristics of terrain that a pilot uses to formulate terrain clearance during low-altitude flight. Those five were: (1) terrain’s texture, (2) irregularity of ground elevation, (3) visible surface detail, (4) known size references, and (5) pilot’s familiarity. Especially important is the fourth characteristic, known size references. These references ensure that size-distance constancy can be kept reliable for retinal image interpretation by helping a pilot estimate height and distance. For example, Figure 4.9 shows an aircraft of known size waiting to take off; another pilot looking at this scene would immediately have a good sense of how far away he was from the other aircraft and the other objects in the surrounding runway scene. In terms of flying a low-level sortie, any object of known dimensions along the route of flight will help a pilot “calibrate his eyeballs” regarding his or her current altitude above the ground. Finally, worth noting is the fifth characteristic, pilot’s familiarity with the terrain and route of flight. Because cognition plays a strong role in visual perception, any route-planning and map-study can greatly assist the pilot with interpretation of the environment’s visual cues.
Haber and Haber (2003) further studied the perceptual and attentional factors and consolidated their findings into four categories of terrain visual information that are especially useful during low-altitude flight:
1. Terrain contour irregularity: The irregularity of terrain geography is one of the main reasons why optical concepts presented earlier such as edge rate fail to provide adequate perceptual cues. Terrain contour irregularity can make it difficult for pilot to predict altitude changes and maintain a constant altitude clearance over the terrain; it will be addressed again in Chapter 6.
2. Terrain texture: this is also a highly variable environmental cue based upon the ground cover across the ground that the pilot is flying over.
3. Linear perspective: the dominant visual cue for aviation depth perception, it is dependent upon sufficient environmental cues to provide the necessary depth perspective.
4. Resolution of fine details of objects on the ground: Calvert (1950, 1954) presented concepts for the use of global and local cues to altitude. For instance, when flying over a field of cows, if the pilot can easily distinguish the cows’ four legs then the aircraft is below 152 m (500 ft). Focal details can later serve as ambient cues when they pass and leave the pilot’s field of view.
According to Haber and Haber (2003), global optic flow is usually the most important source of visual information for maintaining altitude and ground clearance. They stated that, “patterns of optic flow at the retinas geometrically reflect properties of the terrain, both its variation in contour and its distance from the observer” (p. 46). They discussed different hypotheses regarding how ambient cues result in visually guided behavior and concluded that, however the processing occurs, it is automatic and highly informative. The authors presented limitations for efficacious perception of global optic flow for terrain clearance. One limitation included pilot physiology and G-forces restricting peripheral vision. Another optic flow perception issue concerns optic flow rates changing either due to terrain texture or aircraft ground speed. And finally, optic flow rates may be perceptually influenced by the pilot’s prior experience and perceptual adaptation.
Haber and Haber (2003) summarized the pilot’s perceptual and cognitive limitations while flying in the low level environment:
Pilots cannot depend on their automatic perceptual processes during low-altitude flight because misperceptions are likely to occur. As a result, the pilot must engage in three processing steps, all of which require focused attention. First, he has to consciously override automatic processes when they potentially provide him with incorrect information; second, he has to consciously remember to refer to his instrument or other sources for that information; and third, he has to process the alternative sources of information, using focused attention. (p. 46)
As a pilot, the first author can attest to the cognitive load it takes to disregard perceptual information, seek-out and process displayed aircraft status information, and then generate a mental model of the situation. Referring back to the “bucket”—the bucket quickly gets full in the above-mentioned scenario.
The key for a pilot to safely fly low-level sorties is to have a constant cross-check of the aircraft’s altimeter and recalibrate his or her eyes, given the terrain, to that elevation above the ground. Pre-flight map studies can inform the pilot of any drastic terrain elevation changes during the course of the flight. Of course, the best instrument for a pilot is a radar altimeter. This device provides the pilot with instantaneous height information, eliminating the need for mental computation of the difference between current terrain elevation and sea-level elevation. Also, the radar altimeter provides a more accurate value for pilots to calibrate their eyeballs to during environmental perception.
The topic of cognitive attentional demands in aviation is worthy of its own book; here it needs mentioning in order for the reader to appreciate one more aspect of aviation and the pilot’s visual requirements. While there are many possible scenarios that might lead to an increase in cognitive load, two occur frequently in non-emergency situations: instrument flying and the transition from instrument flying to visual flying (or vice-versa). In both cases, accurate perception is crucial, but the lack of ambient cues or the shift in perspective can lead to misperceptions and error.
Reading instrument displays and aircraft status information is completely different from flying visually using environmental perception, where much is done via unconscious ambient processing with a low cognitive footprint, (although focal visual perception is still required for internal cockpit perception). While flying an approach in impoverished visual conditions, it is extremely difficult to perceive environmental cues accurately. It might seem that cognition and attention allocation would be less taxed because of the reduction of information. However, while visual perception of internal cockpit displays is perceptually more accurate, it is also cognitively more challenging. The pilot no longer is making probabilistic and intuitive perceptual visually guided control inputs, but he is making rather deterministic and accurate decisions because of the detail provided by the instrumentation. There is no impoverished viewing environment within the cockpit, but a pilot has high attentional allocation demand for the visual processing of each data source viewed with focal vision, all at the conscious level. A pilot must individually attend to, process, assimilate, and synthesize the aircraft’s navigational and system data. Similar to what occurs when flying visually, all these incoming data sources must be compared with other short-term and long-term memories for the creation, maintenance, and projection of situational awareness—a highly cognitive effort.
Cognitive challenges in the interpretation of perceptual information also arise when pilots flying an instrument approach reach their decision point and they must transition to a visual landing using visual references. At this point, ambient visual information must be attended and rapidly integrated into the pilot’s situational awareness. The decision to land or possibly go-around must be made without hesitation at this point during the approach because the aircraft is close to terrain with the power at lower settings. This transition from instruments flying to a visual landing is ripe for perceptual disorientation due to the abrupt change in attentional demands.
The next chapter presents many of the same aspects of aviation visual perception just shared in this chapter but couched in a human-factors research perspective. Hopefully the examples given in this chapter from a pilot’s perspective will help you appreciate the need for the systematic human factors research that is presented there.
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