February 2006 

NASA/TM-2006-214272 

Dynamic Tunnel Usability Study: Format 

Recommendations for Synthetic Vision System 

Primary Flight Displays 

Jarvis J. Arthur III, Lawrence J. Prinzel III, Lynda J. Kramer, and Randall E. Bailey 

Langley Research Center, Hampton, Virginia 

https://ntrs.nasa.gov/search.jsp?R=20060008164 2018-05-17T09:03:19+00:00Z
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February 2006 

NASA/TM-2006-214272 

Dynamic Tunnel Usability Study: Format 

Recommendations for Synthetic Vision System 

Primary Flight Displays 

Jarvis J. Arthur III, Lawrence J. Prinzel III, Lynda J. Kramer, and Randall E. Bailey 

Langley Research Center, Hampton, Virginia 
Available from: 

NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS) 

7121 Standard Drive 5285 Port Royal Road 

Hanover, MD 21076-1320 Springfield, VA 22161-2171 

(301) 621-0390 (703) 605-6000 
Abstract 

A usability study evaluating dynamic tunnel concepts has been 

completed under the Aviation Safety and Security Program, Synthetic 

Vision Systems Project. The usability study was conducted in the Visual 

Imaging Simulator for Transport Aircraft Systems (VISTAS) III simulator 

in the form of questionnaires and pilot-in-the-loop simulation sessions. 

Twelve commercial pilots participated in the study to determine their 

preferences via paired comparisons and subjective rankings regarding 

the color, line thickness and sensitivity of the dynamic tunnel. The 

results of the study showed that color was not significant in pilot 

preference paired comparisons or in pilot rankings. Line thickness was 

significant for both pilot preference paired comparisons and in pilot 

rankings. The preferred line/halo thickness combination was a line 

width of 3 pixels and a halo of 4 pixels. Finally, pilots were asked their 

preference for the current dynamic tunnel compared to a less sensitive 

dynamic tunnel. The current dynamic tunnel constantly gives feedback 

to the pilot with regard to path error while the less sensitive tunnel only 

changes as the path error approaches the edges of the tunnel. The tunnel 

sensitivity comparison results were not statistically significant. 

Introduction 

Better pilot situation awareness (SA) during low visibility conditions can be provided by 

Synthetic Vision Systems (SVS) displays (Arthur, Prinzel, Kramer, Parrish, & Bailey, 2004; 

Prinzel, Comstock et al. 2004). New technological developments in navigation performance, 

low-cost attitude and heading reference systems, computational capabilities, and displays foster 

the prospect of SVS displays for virtually all aircraft classes. SVS display concepts employ 

computer-generated terrain imagery, on-board databases, and precise position and navigational 

accuracy to create a three dimensional perspective presentation of the outside world, with 

necessary and sufficient information and realism, to enable operations equivalent to those of 

clear-day flight operations regardless of the outside weather or lighting condition. 

Pathway-In-The-Sky Research

Providing pilots the intended flight path as a 3-dimensional perspective path (also referred to as 

“highway in the sky”) has been extensively researched by NASA Langley and others (Prinzel, 

Arthur, Kramer, & Bailey, 2004; Kramer, Prinzel, & Arthur, 2005). For example, Prinzel, 

Arthur et al. (2004) conducted an experiment to determine the best presentation of a pathway-inthe-sky on a SVS primary flight display (PFD). These researchers tested four different tunnel 

formats: Minimal “Crow’s Feet”, Box, Dynamic “Crow’s Feet”, and Dynamic Pathway tunnels. 

The specifications of the four tunnel formats tested are described in Appendix A. 
 2

Prinzel, Arthur et al (2004) reported nonsignificant performance differences between the four 

tunnel concepts. However, subjective data of the experiment evinced that pilots preferred the 

Dynamic Crow’s Feet tunnel. The possible reason for the preference of the Dynamic Crow’s 

Feet tunnel may have to do with its uniqueness; only a portion of the entire tunnel is displayed 

dependent upon path error as a human factors design solution to reduce display clutter but 

preserve informational quality and situation awareness. Behaviorally, the dynamic tunnel grows 

or shrinks as a function of path error in contrast to the typical static tunnel presentation which 

remains fixed to design parameters. Effectively, the dynamic tunnel provides the pilot with the 

boundaries of the flight path through presentation of the corners of the tunnel at all times similar 

to more traditional tunnel formats. However, more traditional tunnels tend to connect and hold 

constant one or more of the dimensions of the tunnel to frame the edges of the flight path. The 

result is that the pilot has significant awareness of how close the aircraft is flying with respect to 

the pathway, but at the cost of display clutter. With a SVS display, such clutter can obscure 

equally important obstacle and terrain information leading to an overall reduction in situation 

awareness. 

The minimal “Crow’s Feet” tunnel was a design attempt to reduce the tunnel display clutter by 

only presenting the corners of the tunnel. Research had shown that, under normal operations and 

when the aircraft is flying down the center of the tunnel, the format is effective but significantly 

loses that effectiveness as the deviation from the desired path increases (Glabb, Kramer, Arthur, 

& Parrish, 2003). Pilots reported that their positional accuracy with respect to the desired path 

was difficult to estimate with the minimal “Crow’s Feet” tunnel format. The Dynamic “Crow’s 

Feet” format, in contrast, merged the Minimal “Crow’s Feet” with traditional tunnel concepts; 

thereby, merging the strengths of both formats. When the path error approaches zero, the 

Dynamic “Crow’s Feet” resembles the Minimal “Crow’s Feet” tunnel but otherwise, adapts to 

provide dynamic feedback to the pilot of how close he or she is to the tunnel boundary. The 

result is a tunnel concept that minimizes clutter yet is flexible and adaptive to ensure high 

situation awareness through dynamic feedback of path error in an intuitive fashion. 

Purpose of Usability Test

A usability test was conducted to evaluate three tunnel design characteristics: tunnel color, tunnel 

line thickness and dynamic tunnel sensitivity. During simulation and flight test experiments, 

some pilots had commented that the dynamic tunnel concept might, in fact, be too dynamic, in 

that, its continual motion can be distracting. One of the concepts tested in Prinzel, Arthur et al. 

(2004) was a less dynamic tunnel than the Dynamic Crow’s Feet known as the Dynamic 

Pathway tunnel. The Dynamic Pathway tunnel mirrors the minimal “Crow’s Feet” tunnel until 

the path error approaches the edge of the tunnel. When the aircraft position is beyond the edges 

of the tunnel boundary, the behavior of the Dynamic Pathway tunnel is similar to the Dynamic 

Crow’s Feet tunnel. However, in Prinzel, Arthur et al. (2004), the Dynamic Pathway tunnel had 

a “floor” which was always present (see Figure 1). Thus, it was conjectured that pilots may have 

preferred the behavior of the Dynamic Pathway tunnel; however, the floor provided too much 

clutter, thus resulting in a lower rating compared to the Dynamic Crow’s Feet tunnel. 

In addition, many features of the tunnel attributes were carried over from the Minimal “Crow’s 

Feet” concept conceived for the High Speed Research (HSR) program, which was a precursor to 

the SVS project. However, these features were not subject to empirical evaluation to their 

efficacy. 
 3

Figure 1: Dynamic Pathway tunnel (left) and the Dynamic “Crow’s Feet” tunnel (right). Note that the tunnel 

“floor” of the Pathway tunnel was not present in the usability study. 

A usability study was conducted to determine the pilot’s preferences for three tunnel 

characteristics, identified on the basis of pilot feedback, which may not be optimal for the 

Dynamic “Crow’s Feet” tunnel. These characteristics are: dynamic tunnel sensitivity, tunnel 

color and tunnel line thickness. 

In this usability study, two tunnel sensitivities were tested. The values were the same 

sensitivities used for the Dynamic Pathway and the Dynamic Crow’s Feet tunnel concepts in 

Prinzel, Arthur et al. (2004). However, for the Dynamic Pathway tunnel, the floor was removed. 

Essentially, this provides a direct comparison between tunnel sensitivities without the floor 

confounding the results. In addition to the dynamic sensitively tunnel comparison, four tunnel 

color combinations and seven different tunnel line thickness combinations were compared. 

Past research has shown that path performance is not significantly affected by the type (i.e., 

Dynamic, Pathway, Minimal, Box) of tunnel symbology (Prinzel, Arthur et al., 2004). 

Quantitative path performance differences between these concepts would not be expected. On 

this basis, a usability study, wherein the relevant metrics are only qualitative, should provide 

valid, accurate results for these comparisons. 

Methodology 

Usability Participants

A total of 12 subjects were used in the usability study. The subject pool consisted of 11 

commercial pilots (first officers and captains) and 1 FAA pilot. The subjects who took part in 

the usability study were participants in an earlier experiment which used the dynamic tunnel. 

Since the usability study immediately followed the experiment, subjects were familiar with the 

dynamic tunnel symbology. Three attributes of the tunnel were evaluated through interactive 

questionnaires and short simulation sessions. The simulation sessions were conducted in the 

Visual Imaging Simulator for Transport Aircraft Systems (VISTAS) III, a part task simulator 

Pathway Dynamic
 4

used for concept development for advanced commercial cockpit displays. The concepts were 

displayed on a ARINC Size D (7.0 inch square viewable display surface) head down display with 

a resolution of 768 horizontal pixels over a field of view of 30 degrees. The distance between 

the eye reference point and the center of the display was 28 inches. The total time for the 

usability study for each subject was 30 minutes. 

Usability Procedure

First, pilots were asked their opinion of the color of the tunnel by answering a paired comparison 

(Appendix B) questionnaire while looking at static pictures of the tunnel concept (see Figure 2). 

In addition, pilots rank-ordered their preference for tunnel color during the final questionnaire. 

The paired comparisons were done interactively to ensure accurate data collection and to provide 

a rationale for each of the four colors; magenta, green, white and black. 

Historically, the SVS project has used magenta as the tunnel color because magenta is the color 

of the active pathway on the navigation display. Therefore, a magenta 3-dimentional projection 

of this path on the PFD provides visual consistency between the PFD and navigational display. 

In addition, since the PFD guidance cue is magenta, a magenta tunnel provided reinforcement 

cueing that all of the magenta symbologies work in concert. However, in past simulation and 

flight test experiments pilot subjects have commented that this can lead to too much magenta 

symbology on the display, especially in turns. Evaluation of a white color was chosen to 

maintain consistency with the other PFD symbologies (e.g., pitch ladder, horizon line, etc). 

Though white has a good contrast ratio, white tunnel segments could overlap other symbologies 

(for example, the pitch ladder tick marks) making it hard to distinguish the tunnel shape. Green 

was chosen as a tunnel evaluation color as no other symbology is green; thus, it should be easily 

and uniquely interpreted. Finally, black was chosen as an evaluation color as it was considered 

to provide the same benefits as the green color. 
 5

Figure 2: Four color choices; Magenta, Green, White and Black. 

The pilot’s preferred color was then used in a simulation session to determine the ideal tunnel 

line and halo width. Haloing is a technique used to provide a high-contrast (black) background 

so that the primary color can be more easily distinguished. For example, the centerline, 

threshold and runway number markings are painted in white with a thin black border. This black 

border, known as haloing, provides color contrast so that the markings can be easily seen on the 

runway. 

Symbology “thickness” is measured as total pixels in width. For example, with a tunnel 

thickness of 2 pixels and a halo thickness of 4 pixels; 2 pixels of the tunnel overlay the halo and 

only one pixel (each side) of halo (black pixels) around the tunnel will be visible. If the halo 

thickness is the same size as the symbology, a halo will not be visible. The software used to 

render the various tunnel concepts was written in OpenGL. OpenGL allows developers to 

specify line widths as floating point numbers, thus non integer line thicknesses are possible 

(Woo et al. 1997). Antialiasing was enabled via the graphics card. 
 6

Pilots flew a curved, descending approach known as the Sparks East Visual Arrival to Runway 

16R at Reno, NV. Pilots were shown 7 different tunnel and halo line thickness combinations 

described in Figure 3. Note, for the black tunnel symbology color usability condition, there is no 

haloing; thus, only 4 line thickness variations (0.5, 1.0, 2.0, and 3.0) for the black tunnel were 

evaluated. The simulation began with the thinnest concept, known as Concept A, and progressed 

at the pilot’s discretion until the thickest tunnel concept was observed. The simulation session 

was interactive and concepts were changed in real-time to let the pilot compare each concept. 

Once a preferred tunnel and halo line thickness was determined, a paired comparison was 

performed for the 7 line thickness concepts. 

Figure 3: The 7 tunnel (shown in magenta) and halo line thickness concepts used in the usability study. 

Concept A 

 Tunnel width: 0.5 pixels 

 No Halo 

Concept B 

 Tunnel width: 1.0 pixels 

 Halo width: 1.5 pixels 

Concept C 

 Tunnel width: 2.0 pixels 

 No Halo 

Concept F 

 Tunnel width: 3.0 pixels 

 No Halo 

Concept D 

 Tunnel width: 2.0 pixels 

 Halo width: 3.0 pixels 

Concept E 

 Tunnel width: 2.0 pixels 

 Halo width: 4.0 pixels 

Concept G 

 Tunnel width: 3.0 pixels 

 Halo width: 4.0 pixels 

Halo 

Width 

Tunnel 

Width 
 7

At the completion of the tunnel and halo line thickness paired comparison, another short 

simulation session was conducted to determine the preferred sensitivity of the dynamic tunnel. 

Pilots were shown two PFD’s side-by-side to evaluate the tunnel sensitivity. One PFD showed 

the Dynamic Crow’s Feet and the other showed the Dynamic Pathway. 

Figure 4 shows the path error curves for both dynamic tunnels which define the tunnel segment 

lengths, and thus, define the dynamic sensitivity. A tunnel segment length of 100% is equivalent 

to a fully connected box tunnel (see the Box tunnel in Figure A1 of Appendix A). The Dynamic 

Crow’s Feet was the most sensitive dynamic tunnel constantly changing as function of path 

error. Therefore, unless the pilot was perfectly on path, the tunnel would provide continuous 

feedback as to the instantaneous path error. In comparison, the Dynamic Pathway would not 

change dynamically until a quarter-dot path error (either lateral or vertical) had been reached. 

Thus, as long as the pilot stayed within a quarter-dot path error, the tunnel geometry would not 

change. If the path error exceeded a quarter-dot, then the tunnel would provide dynamic 

feedback as to the path error like the Dynamic Crows Feet tunnel. 

Figure 4: The path error curve defined for each dynamic tunnel concept. 

After the preferred dynamic tunnel was chosen, a final rank-ordering was done for the tunnel 

color, tunnel and halo line thickness and sensitivity. 

Tunnel Segment Length as a Function of Path Error for the Two 

Dynamic Tunnels in the Usability Study

0

20

40

60

80

100

-1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1

Path Error (dot)

Tunnel segment length (%)

Pathway (less sensitive)

Dynamic (more sensitive)
 8

Results 

Color 

An Analysis of Variance (ANOVA) test was performed on the tunnel color attribute. Color 

preference was not statistically significant in the paired comparisons (p=0.129) nor in pilot 

rankings (Friedman test; p=0.138). The tunnel color preference, in order based on the mean rank 

from the Friedman test, was green (1.82) followed by magenta (2.36), white (2.82) and the least 

preferred, black (3.0). 

Tunnel and Halo Line Thickness 

An ANOVA test was performed for tunnel and halo line thickness preference pairedcomparisons. Tunnel line thickness was significant (excluding pilots who chose black as 

preferred color F(6,54) = 3.664, p<.05) for the paired comparisons as well as pilot rankings 

(Friedman test; p<.05). Concept G (tunnel line thickness of 3 pixels and halo thickness of 4 

pixels) was the preferred tunnel thickness. 

It should be noted that the pixel is just one measure for the size of the symbology and additional 

evaluations may be needed for further specification. For example, for smaller or larger display 

devices, the angle subtended by one pixel varies proportionally to the display device size and 

resolution. For this study, the display device measured 7.0 inches over 768 pixels resulting in 

110 pixels per inch resolution. 

Dynamic Tunnel Sensitivity 

For tunnel sensitivity, exactly half of the pilots (6 of the 12) chose the high sensitivity tunnel 

concept (Dynamic Crow’s Feet) and the other 6 chose the less sensitive tunnel concept (Dynamic 

Pathway). Pilots who preferred the Dynamic Crow’s Feet tunnel stated that it provides instant, 

intuitive feedback of the path error. In addition, since it was rare for subjects to be exactly on 

path, the Dynamic Crow’s Feet tunnel provided more definition of turn segments. The result 

was a clearer depiction of the turn making the tunnel easy to interpret. For the Pathway Tunnel, 

the tunnel segments in a turn were not long enough to clearly define the turn for the pilot. 

Those subjects who chose the Dynamic Pathway tunnel preferred having less movement. They 

felt the Dynamic Crow’s Feet was too distracting by providing constant tunnel changes. They 

preferred using the guidance symbol to “fine-tune” flying the path. Further, they liked how the 

tunnel boundaries changed as they approached the tunnel edge to alert of gross errors rather than 

constant small errors. 
 9

Pilot Preferences 

Table 1 lists each subject pilot’s top rated attribute for the tunnel. 

Table 1: Tunnel attribute preferences for each test subject pilot. 

Pilot Color Tunnel Line Width (TW) and 

Halo Width (pixels) 

Dynamic Tunnel Sensitivity 

1 Green Concept G (TW 3.0, Halo 4.0) Pathway (Less Tunnel Movement) 

2 Green Concept E (TW 2.0, Halo 4.0) Dynamic Crow’s Feet (Most Movement) 

3 Magenta Concept G (TW 3.0, Halo 4.0) Pathway (Less Tunnel Movement) 

4 Magenta Concept G (TW 3.0, Halo 4.0) Dynamic Crow’s Feet (Most Movement) 

5 Green Concept E (TW 2.0, Halo 4.0) Pathway (Less Tunnel Movement) 

6 Green Concept D (TW 2.0, Halo 3.0) Pathway (Less Tunnel Movement) 

7 Black Concept A (TW 3.0) Dynamic Crow’s Feet (Most Movement) 

8 White Concept D (TW 2.0, Halo 3.0) Dynamic Crow’s Feet (Most Movement) 

9 Green Concept F (TW 3.0, No Halo) Pathway (Less Tunnel Movement) 

10 Green Concept F (TW 3.0, No Halo) Pathway (Less Tunnel Movement) 

11 Magenta Concept E (TW 2.0, Halo 4.0) Dynamic Crow’s Feet (Most Movement) 

12 Black Concept C (TW 3.0) Dynamic Crow’s Feet (Most Movement) 

Conclusions 

A usability study of a 3-dimensional tunnel pathway on a primary flight display was conducted 

for the three tunnel attributes of color, line width, and dynamic sensitivity. The results showed 

that tunnel color was not significant, however, a green tunnel was preferred when presented with 

white HUD symbology and a green/brown hybrid textured terrain database. The line and halo 

line thickness of the tunnel was significant as pilots preferred the tunnel thickness of 3 pixels and 

a halo thickness of 4 pixels. Finally, the pilot preference was evenly split where half of the 

subjects chose the Dynamic Crow’s Feet tunnel compared to the Dynamic Pathway tunnel. 

The results of the usability study evince the existence of significant individual differences in the 

determination of optimal tunnel portrayal. While not conclusive, the data suggest that certain 

combinations of color and line width are not acceptable candidates specifically for Synthetic 

Vision displays. Statistical evidence and, particularly, pilot comments imply certain 
 10

characteristics are less favorable such as the use of white coloring, thin line widths, and thick 

haloing. Black coloring was typically noted to be an acceptable color because of its substantial 

contrast with the terrain background. However, most pilots noted the unfavorable aesthetics 

when presenting a black tunnel on a synthetic terrain background. Based on pilot comments, 

designers should consider employing magenta or green tunnel coloring with tunnel thickness of 

at least 3 pixels and black haloing. Since the tunnel is used by the pilots as a second order 

guidance cue, the tunnel needs to be prominent without providing adverse clutter. 

Past studies demonstrated the enhanced situation awareness afforded through precision 

positioning information of the dynamic tunnel concept (Prinzel, Arthur et al., 2004). 

Unfortunately, the data from this usability study did not indicate any trends or conclusion for 

preferable or optimal dynamic tunnel sensitivities. Future studies should examine several levels 

of dynamic flight path presentation that cover the gamut of potential dynamic tunnel designs. 

The tunnel attributes found to be preferred in this usability test were tested using the NASA 

hybrid terrain texture concept for a primary flight display. Other Synthetic Vision displays, such 

as head-up and helmet-mounted displays, and different display concepts, such as those 

employing photo realistic, generic texturing, wire-frame, and other terrain texturing, may 

discover different results because of the highly interactive nature of tunnel presentation with the 

background terrain. Therefore, display designer seeking to employ pathway-in-the-sky 

symbology should consider these results herein as well as empirically evaluate the human factors 

involved in specific design of these formats as part of Synthetic Vision displays. 

REFERENCES 

Arthur, J.J., Prinzel, L.J., Kramer, L.J., Parrish, R.V., & Bailey, R.E. (2004). Flight Simulator Evaluation of 

Synthetic Vision Display Concepts to Prevent Controlled Flight Into Terrain (CFIT). NASA TP-2004-213008. 

Bennett, K.B., & Flach, J.M. (1994). When automation fails.... Human performance in automated systems: Current 

research and trends (pp. 229-234). Hillsdale, NJ: Lawrence Erlbaum Associates. 

Boeing (1998). Statistical summary of commercial jet aircraft accidents, Worldwide Operations, 1959-1997. Seattle, 

WA: Airplane Safety Engineering, Boeing Commercial Airplane Group 

Enders, J.H., Dodd, R., Tarrel, R., Khatwa, R., Roelen, A.L.C., & Karwal, A.K. (1996). Airport safety: A study of 

accidents and available approach-and-landing aids. Flight Safety Digest, 1996(3), 1-36. 

Glabb, L. J., Kramer, L. J., Arthur, J. J., & Parrish, R.V. (2003). Flight Test Comparisons of Synthetic Vision 

Display Concepts at Dallas/Fort Worth International Airport. NASA TP-2003-212177. 

Haskell, I.D., & Wickens, C.D. (1993). Two- and three-dimensional displays for aviation: A theoretical and 

empirical comparison. International Journal of Aviation Psychology, 3, 87-109 

Hemm, R.V. (2000). Benefit estimates of synthetic vision technology. NASA Langley Research Center: NASA 

Contractor Report NS002S1. 

Kramer, L.J., Prinzel, L.J., Bailey, R.E., & Arthur, J.J. (2003). Synthetic vision enhances situation awareness and 

RNP capabilities for terrain-challenged approaches. Proceedings of the American Institute of Aeronautics and 

Astronautics Third Aviation Technology, Integration, and Operations Technical Forum, AIAA 2003-6814, 1-11. 
 11

Kramer, Lynda J.; Prinzel III, Lawrence J.; and Arthur III, Jarvis J (2005).: Advanced Pathway Guidance 

Evaluations on a Synthetic Vision Head-Up Display. NASA TP-213782, July 2005. 

Merrick, V.K., Jeske, J.A., “Flight Path Synthesis and HUD Scaling for V/STOL Terminal Area Operations,” 

NASA TM-110348, April 1995. 

National Aeronautics and Space Administration (2001). Aerospace Technology Enterprise. Washington, D.C.: 

NASA. 

Prinzel, L.J., Comstock, J.R., Glaab, L.J., Kramer, L.J., Arthur, J.J., & Barry, J.S. (2004). The efficacy of headdown and head-up synthetic vision display concepts for retro- and forward-fit of commercial aircraft. 

International Journal of Aviation Psychology, 14, 53-73. 

Prinzel, L.J., Arthur, J.J., Kramer, L.J. & Bailey, R.E. (2004). Pathway Concepts Experiment for Head Down 

Synthetic Vision Displays. SPIE. In J. G. Verly (Ed.), Proceedings of the SPIE, Enhanced and Synthetic Vision 

2004, 5424-02, pp. 11-22. 

Prinzel, L.J., Hughes, M.F., Arthur, J.J., Kramer, L.J., Glaab, L.J., Bailey, R.E., Parrish, R.V., & Uenking, M.D. 

(2003). Synthetic Vision CFIT Experiments for GA and Commercial Aircraft: “A Picture Is Worth A Thousand 

Lives”. Proceedings of the Human Factors & Ergonomics Society, 47, 164-168. 

Prinzel, L.J., Kramer, L.J., Bailey, R., Hughes, M., & Comstock, R. (2002). NASA Eagle-Vail Synthetic Vision 

Flight Test. Proceedings of the Human Factors and Ergonomics Society 46th Annual Meeting, 46.135-139 

Prinzel, L.J., Kramer, L.J., Comstock, J.R., Bailey, R.E., Hughes, M.F., & Parrish, R.V. (2002). NASA synthetic 

vision EGE flight test. Proceedings of the Annual Human Factors and Ergonomics Meeting, 46, 135-139. 

Schnell, T., Kwon, Y, Merchant, S., & Etherington, T. (2004). Improved flight technical performance in flight decks 

equipped with synthetic vision information system displays. International Journal of Aviation Psychology, 14, 

79-102. 

Theunissen, E.R. (1997). Integrated design of a man-machine interface for 4-D navigation. Delft, Netherlands: Delft 

University Press. 

Wiener, E. L. (1977). Controlled flight into terrain accidents: System-induced errors. Human Factors, 19, 171-181. 

Williams, D., Waller, M., Koelling, J., Burdette, D., Doyle, T., Capron, W., Barry, J., & Gifford, R. (2001). 

Concept of operations for commercial and business aircraft synthetic vision systems. NASA Langley Research 

Center: NASA Technical Memorandum TM-2001-211058. 

Williams, K.W. (2002). Impact of aviation highway-in-the-sky displays on pilot situation awareness. Human 

Factors, 44, 18-27. 

Woo, M., Neider, J., & Davis, T. (1997). OpenGL Programming Guide, Second Edition. Addison Wesley 

Developers Press. 
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Appendix A 

Four tunnel (box, minimal, dynamic “crows feet”, dynamic pathway) and baseline (i.e., no 

tunnel) concepts were evaluated (see Figure A1) in the paper by Prinzel, Arthur et al. (2004), 

“Pathway Concepts Experiment for Head Down Synthetic Vision Displays.” The "box" tunnel, a 

concept that is the subject of most of the tunnel research in the literature, consisted of a series of 

boxes connected at the corners to form a path within which the pilot flies. It was presented out to 

a length of 10 nm, with no fading. The minimal tunnel concept consisted of a series of "crows 

feet" presented in each corner of a tunnel segment (essentially a truncated box). The tunnel 

presentation was 5 tunnel segments per nautical mile (nm) with a total length of 3 nm, which 

faded linearly to invisibility. The third concept, dynamic "crows feet", allowed the "crow’s feet" 

to grow as a function of path error. Therefore, the pilots are given feedback as to where they are 

in the tunnel and if they are in danger of flying out of the tunnel. The idea of the dynamic tunnel 

was that if the pilot is flying in the center of the tunnel, there should be the smallest amount of 

clutter. However, if there exists appreciable path error, the tunnel walls would "grow" to help the 

pilot gauge where the boundaries of the tunnel are. This helps to overcome a frequent criticism 

of "low clutter" tunnels. The fourth concept, dynamic pathway, was a variation of the dynamic 

"crows feet" concept in which the floor of the tunnel was presented at all times. For both the 

dynamic pathway and dynamic “crows feet”, when the pilot left the tunnel, the tunnel would 

change to a “trough” and resemble a box tunnel with the exception that the tunnel would open to 

“invite” the pilot back into the tunnel (Figure A2). 

The results indicated that the presence of a tunnel had a marginal effect on enhancing path 

control performance for the head-down display compared to the baseline (no tunnel w/ ball 

guidance). No significant differences, however, were found for path control performance 

between the four tunnel concepts. Despite this, statistically significant differences were found 

for pilot ratings for situation awareness and workload. Overall, pilots rated the tunnel concepts 

to be significantly better in terms of workload and situation awareness compared to not having a 

tunnel present. When just the tunnel concepts are considered, the minimal tunnel concept was 

consistently rated poorer followed by the box tunnel concept. The reasons are different for the 

two tunnel concepts. The minimal tunnel was found to be poor for situation awareness because 

it was difficult to accurately determine where you were in the tunnel. However, pilots did note 

that the presence of the guidance symbology and path deviation indicators significantly reduce 

this problem. Furthermore, all pilots remarked that the minimal tunnel might be optimal for a 

HUD where issues of clutter are of particular concern compared to the PFD. The box tunnel, in 

contrast, was rated poorer because of concerns of clutter especially on final approach. Although 

it was fairly easy to determine where they were in the tunnel, the advantage was negated because 

the tunnel obscured the synthetic terrain. For these reasons, the evaluation pilots preferred the 

dynamic tunnel concepts for a head-down synthetic vision display. 

Overall, the dynamic pathway was rated very high for situation awareness, but several pilots 

reported that the presence of the tunnel floor (“railroad track”) was unnecessary when compared 

to the dynamic “crow’s feet” tunnel. Therefore, although preferred to the minimal and box 

tunnel concepts, the dynamic “crow’s feet” was reported to provide all the advantages of the 

dynamic pathway with less clutter. All pilots remarked that the dynamic quality of the tunnel 

was useful to determine exact position within the tunnel and the “trough” effect when outside the 

tunnel made it very easy to re-enter the tunnel. However, most pilots thought that the tunnel may 

have been too dynamic and somewhat distracting. Therefore, the algorithm for the dynamic 

“crow’s feet” tunnel will be redesigned to reduce this issue. 
 13

Minimal

Dynamic

Box

Pathway

Figure A1: Tunnel Symbology Concepts used in the Pathway Concepts Experiment. 

Figure A2: Dynamic “Crow’s Feet” Tunnel Concept 
 14

Appendix B 

Color Paired comparison questionnaire completed by the subjects 

Overview: This questionnaire is designed to allow statistical analysis of your subjective 

assessment of your preferences for tunnel color and line width/halo that you saw today. Please 

look at the pictures of the display concepts when making your comparisons. 

Paired Comparison Rating Instructions: Each paired comparison will be listed on the left side 

of the questionnaire. 

Pilot Preference (Tunnel Color) If not equal, how much more or how much less? 

Barely Substantially 

White + Black Halo 

is (___ more)( ___ equal)( ___ less) preferred than 

Green + Black Halo 

White + Black Halo 

is (___ more)( ___ equal)( ___ less) preferred than 

Black + None 

White + Black Halo 

is (___ more)( ___ equal)( ___ less) preferred than 

Magenta + Black Halo 

Green + Black Halo 

is (___ more)( ___ equal)( ___ less) preferred than 

Black + None 

Green + Black Halo 

is (___ more)( ___ equal)( ___ less) preferred than 

Magenta + Black Halo 

Black + None 

is (___ more)( ___ equal)( ___ less) preferred than 

Magenta + Black Halo 
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Dynamic Tunnel Usability Study: Format Recommendations for Synthetic

Vision System Primary Flight Displays

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Arthur, Jarvis J., III; Prinzel, Lawrence J., III; Kramer, Lynda J.; and

Bailey, Randall E.

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-19218

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

An electronic version can be found at http://ntrs.nasa.gov

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 03

Availability: NASA CASI (301) 621-0390

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

A usability study evaluating dynamic tunnel concepts has been completed under the Aviation Safety and Security Program, Synthetic Vision Systems Project.

The usability study was conducted in the Visual Imaging Simulator for Transport Aircraft Systems (VISTAS) III simulator in the form of questionnaires and

pilot-in-the-loop simulation sessions. Twelve commercial pilots participated in the study to determine their preferences via paired comparisons and subjective

rankings regarding the color, line thickness and sensitivity of the dynamic tunnel. The results of the study showed that color was not significant in pilot

preference paired comparisons or in pilot rankings. Line thickness was significant for both pilot preference paired comparisons and in pilot rankings. The

preferred line/halo thickness combination was a line width of 3 pixels and a halo of 4 pixels. Finally, pilots were asked their preference for the current

dynamic tunnel compared to a less sensitive dynamic tunnel. The current dynamic tunnel constantly gives feedback to the pilot with regard to path error while

the less sensitive tunnel only changes as the path error approaches the edges of the tunnel. The tunnel sensitivity comparison results were not statistically

significant.

15. SUBJECT TERMS

Highway in The Sky (HITS); Primary Flight Display; Synthetic Vision; Tunnel Pathway

18. NUMBER

 OF 

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19

19b. TELEPHONE NUMBER (Include area code)

(301) 621-0390

a. REPORT

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c. THIS PAGE

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b. ABSTRACT

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17. LIMITATION OF 

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Standard Form 298 (Rev. 8-98)

3. DATES COVERED (From - To)

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

609866

11. SPONSOR/MONITOR'S REPORT

 NUMBER(S)

NASA/TM-2006-214272

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY)

01- 02 - 2006