HUMAN
F A C T 0 RS, 1978,20(5), 529-536
Collision Avoidance Response Stereotypes in Pilots and Nonpilots DENNIS B. BERINGER', University o f Illinois at Urbana-Champaign
A two-part study was conducted to investigate the effects of target variables upon pilot and
nonpilot collision avoidance responses to simulated approaches which were head-on or nearly so. Part I investigated the effectof bearing and found that nonpilots preferred to turn lefi in a head-on approach.Although pilots generally turned right under the same conditions, 25% exhibited the nonpilot left-turn response. The nonpilot response bias seemed related to the type of control used for aircraft pilotage. Part I1 examined the effects of bearing and collision index (a geometric construct representing an index for optimal response selection) upon the responses of 24 pilots. Two subgroups were identified, one apparently attending primarily to bearing while the other attended to aspect. Only one subject appeared to use the optimal collision-index construct for response selection.
INTRODUCTION
The Pilot Task
A hazard encountered in present highThree sequential steps are necessary in the density air traffic operations is the mid-air maintenance of separation by visual means. collision. A summary of the incidents in 1968 These steps are detection, response selection, compiled by the National Transportation and response execution. Although much has Safeiy Board (NTSB,July 1969) indicated been done in the areas of target detection that such incidents were a real and present (Hanff and Pessa, 1966; Crook, 1970; Graham, danger while recent accident reports (NTSB, 1971) and response selection (Friedlander, 1974-1975,s volumes) indicate that the prob- 1970; Bates, Fletcher, Michnick, and Prast, lem persists despite many attempts to elimi- 1968) by machine systems, the prohibitive nate it. A general characterization of the costs of these systems (United States General mid-air collision drawn from the NTSB Accounting Office, 1974) greatly restrict their summary (Crook, Sulzer, and Hill, 1972, and use. For present purposes both adequate visSimpson, Rucker, and Murray, 1973) places ual detection and unaided response selection collision occurrences during operations will be assumed. where the pilot is responsible for maintaining Regulations have been structured (Federal adequate separation by visual means. It apAviation Regulations, Part 91.67) a n d pears necessary, then, to examine those tasks strategies developed (Crook, Sulzer, and Hill, which the piIot must perform to maintain 1972; Crook, 1969) to assist the unaided pilot this separation. in selecting appropriate maneuvers for maintaining separation. Beringer (1971) con' Requests for reprints should be sent to Mr. Dennis B. ducted a preliminary study involving the Beringer. Department of Psychology, University of Illinois at Urbana-Champaign,Champaign, Illinois 61820, U.S.A. Federal Aviation Regulation (FAR) governing Downloaded at Monash University on June 5, 2016 @ 1978.The Human Factors Society. Inc. from hfs.sagepub.com529 All rights reserved.
HUMAN
530-October, 1978
right of way in head-on or nearly head-on approaches. The regulation, believed derived from maritime law, requires both pilots to alter aircraft course to the right. The experiment, using a simulated auditory proximity warning indicator but no visual targets, revealed that one of every four licensed pilots examined turned left to avoid the instructionally defined head-on collision. The nonpilot response stereotype was a left turn, suggesting that the general population response interfered with selection of the FARspecified right turn by some pilots. Variables AffectingResponse
Two of the major classes of variables that influence the selection of a control response to an imminent collision threat are those affecting the appearance and position of the target (target variables) and those influencing pilot response skills (pilot variables). Although both hardware and environmental variables may also influence pilot behavior, the present discussion is restricted to the first two classes because they can be generalized across all mid-air encounters. Target variables. Although detection may be affected by target size, targedground contrast, location in the visual field, and target motion, Crook (1970) and Ross (1960) have emphasized that targets in collision approaches appear to have little or no motion relative to the observer. Thus, aspect and bearing appear to be prime variables for investigation. Aspeci can be thought of as variations in target appearance caused by rotating the target aircraft about its yaw (vertical) axis. In the absence of motion cues aspect should indicate the target's direction of travel. Bearing is the angle, in the horizontal plane, between thecenterlineof theobserver aircraft fuselage and a line connecting the target and observer. Although the pilot may not be seated on the fuselage centerline. the parallax is so slight for the distances involved that bearing may be measured from the aircraft centerline. Another observation of Crook (1969) showed that 40% of the mid-air collisions from 1964 through 1968 had convergence angles of
FACTORS
0 to IOdegrees(head-on)or 171 to 180degrees.This was confirmed in a larger sample by Simpson, Rucker. and Murray (1973). The range of values investigated, then, might be reduced to those within these limits.
Pilot variables. The prior experience which pilots have had with particular types of aircraft may result in negative transfer in some situations. Previously appropriate responses may become inappropriate or interfere with task performance. With this possibility in mind it is of interest to examine the flight histories of pilots with the intent of relating past experience to present performance. Purpose of Present Study
Utilization of the observations of Crook (1970). Ross (19601, Crook (19691, a n d Simpson et al. (1963) permitted a restriction of both the types and ranges of variables to be examined. Aspect and bearing should provide approach geometry information where no apparent target motion exists. Bearing values were restricted to those accounting for the majority of collisions. Aspect values were restricted to those which, in combination with the selected bearing values, would represent a reasonable collision threat configuration. Two phases of experimentation were designed to investigate the effects of these variables upon collision avoidance behavior. The first phase was intended to attempt confirmation of the nonpilot stereotypic response to head-on approaches as compared with that of trained pilots. The second phase was designed to evaluate the effects of selected values of bearing and aspect upon pilot collision avoidance behavior. PART I The first experiment was designed to examine pilot and nonpilot responses to head-on, or nearly so, collision approaches. This phase, using a motion-base simulator, visual targets, and a realistic flight task, served as an extension and elaboration of the earlier Beringer (1971) study.
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
DENNIS B. BERINGER
October, 1978-531
Method Three groups of 12 subjects each, composed of male nonpilots, female nonpilots, and male pilots respectively, were tested in a Link GAT-1 single-place flight training simulator. A rear projection system used with the simulator produced both a horizon and target images, Targets were white, positive-contrast aircraft silhouettes (Cessna 177) subtending two degrees of visual arc at zero degrees bearing. Although target bearing could assume any value from 355 degrees (five degrees left) to 005 degrees (five degrees right) in onedegree increments, target aspect was always head-on (zero). Both pilots and nonpilots were required to maintain the simulator in a level flight attitude with pitch and roll motion active while searching for aircraft targets. Subjects were required to execute an avoidance maneuver (turn) upon detection of an intruder aircraft, returning the simulator to Ievel flight upon disappearance of the target aircraft. Nonpilots received a short period of instruction, usually 15 to 20 minutes, in controlling the pitch and bank of the simulator. This instruction was sufficient t o give the subject adequate control over the simulator for the purposes of the experiment. Stimulus presentations were distributed such that five targets appeared at each bearing except zero degrees (centerline) where ten targets appeared. Repeated presentations generated a probability of lefthight turn over trials for each subject at each stimulus level. The targets appeared in a predetermined random order with randomly selected interstimulus intervals ranging from 8 through 14 seconds..Half of the center presentations were preceded by left-of-center targets and half by right-of-center targets. Although direction of turn was the dependent variable of primary interest as measured by recording bank angle, pitch angle was also
recorded by a two-channel paper strip chart ~. recorder. This allowed evaluation of preference for vertical components in the avoidance maneuver. A stimulus event marker indicated stimulus onset and offset. Previous pilot experience, hand preference, and eye dominance were assessed by means of a post-test questionnaire and interview. ResuZts A two-way analysis of variance was conducted on probability of a left turn by bearing and group membership. Effects of both bearing,F (10.330) = 7 5 . 4 7 , ~< 0.0001,and group membership, F(2,33) = 5.21, p < 0.01, were found to be significant. Scheffe post hoc comparisons at zero degrees bearing, a point of particular interest, showed no reliable difference between the male and female nonpilot groups (see Figure l), the females being more variable a s a group than the males. A similar comparison indicated that these two groups combined were reliably different from the pilot group ( p = 0.014). Nonpilot males and females had a higher median probability of turning left a t zero degrees bearing (0.80
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Figure 1. Median probabi&,of a left and group.
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
by haring
HUMAN
532-0ctober, 1978
and 0.60 respectively) than did the pilots (0.25). Three pilots, however, exhibited individual left-turn probabilities [ p (left)] at the centerpoint exceedingp(1eft) = 0.50, thus confirming Beringer's (1971) earlier finding which showed that 25% of the pilot population exhibited a left-turn bias. Neither reliable relationships between pilot experience and task performance nor reliable vertical deviation patterns appeared, although some pilots verbally expressed a preference for a climbing turn when interviewed afterwards. Discussion
Clearly, the stereotypic responses of nonpilots were quite different from those of pilots such that nonpilots preferred to turn left. The education of pilots according to the Federal Aviation Regulation requiring a right turn to avoid a head-on collision would appear to be less than 100% effective, because 25% of the pilots exhibited the typical nonpilot response. All the pilots in'this sample indicated a correct knowledge of the regulation in answering the post-test questionnaire. These pilots preferred to turn left even though they knew the regulation required the opposite response. Two questions arose subsequent to this investigation regarding the nonpilot stereotype. Perhaps the nonpilot bias could be attributed to some inherent motion tendency of the GAT-1 system. If not, a means of isolating the causal factor was desirable. Examination of the nonpilot responses to the questionnaire item asking if any differential ease of turn initiation had been noticed revealed no systematic bias to the responses. The fact that the stereotype was also observed in a simulation of a different type (Beringer, 1971) further suggested that the effect was not due to some systematic bias in the GAT-1. To clarify this question further a short investigation was then conducted outside the confines of the flight simulator to determine
FACTORS
whether the nonpilot bias was an internalized choice effect o r the result of a machinerelated factor. Twenty-four nonpilots, 12 male and 12 female, were presented the same forced-choice paradigm as that presented to subjects who operated the GAT-1. The PLAT0 1V computer display system was used for stimulus presentation and response recording. Subjects indicated response selection by single key presses when an aircraft target appeared on the plasma panel display. No systematic response bias was observed in this investigation. Restriction of the effect t o the flight simulators suggests that a characteristic common to both might be influencing response execution. The only characteristic common to both was the control yoke. It is not sufficient to say that flying with only the left hand on the yoke, as pilots do, makes the downward pull t o turn left the easier response because most nonpilots used both hands to manipulate the yoke. Anthropometric data (Van Cott and Kinkade, 1972)seem to suggest that more force can be exerted upward by the right hand on a vertical handgrip than b y the left hand, downward forces available being about equal. This would seem to favor the counterclockwise rotation for a left turn. Caution should be used in this approach, however, for as the elbow angle is decreased from 150 degrees to 90 degrees, the difference disappears. A similar argument may be developed for the stick configuration controller. PART I1 The second phase of experimentation was designed to examine the effects of bearing and aspect upon pilot selection of avoidance maneuver. Bearing and aspect were combined in a systematic manner to produce a new geometric construct called collision index (bearing minus aspect). This construct
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
October. 1978-533
DENNIS B. BERINGER
should provide an index of collision occurrence if both aircraft have approximately the same airspeed, a collision occurring when the value is equal to zero. It is plausible, then, that pilot response strategy could be based upon bearing, aspect, or collision index. Response Strategies Bearing. A strategy based upon bearing suggests that target location relative to the observer determines his response selection without consideration of target aspect. All bearings left of the visual centerline should cause a right-turn response [p(left) = 01;all bearings right of centerline should produce left turns [p(left) = 11. At a zero-degree bearing (head-on) the situation should prove ambiguous and result in p(1eft) = 0.5. Aspect. Processing in terms of target aspect suggests that for aspect values where the nose of the target aircraft is pointed to the observer’s left, p(1eft) = 0 should result. Values showing the nose to the right should produce p(1eft) = 1. A head-on aspect should produce p(1eft) = 0.5. Collision index. Evaluation of targets in terms of approach geometry, the collision index, would producep(1eft) = 0 for targets passing to the observer’s left and p(1eft) = 1 for targets passing to the right. The ambiguous case where collision index equaled zero should result in p(1eft) = 0.5. In this study collision index was assigned right and left labels such that it indicated in which direction the observer should turn, not the side to which the target would pass. Thus a target passing to the left would have a right collision index requiring a right turn.
degrees left of center to 20 degrees right of center were paired with seven values of collision index which ranged from 15 degrees left to 15 degrees right. Both covered their ranges by five-degree increments. Each combination of levels occurred once during the stimulus presentations with the exception of zerobearing-zero-collision-index. Nine presentations were added for this combination so that the data obtained a t this point could be directly compared with data obtained in Part I. Of the 24 pilots (22 males, 2 females) who participated, two were assigned to each of 12 stimulus presentation orders. Six of the orders were randomly generated with the remaining six being derivations of these random orders. The experimental task and instructions were essentially the same a s in Part I with minor revisions. A warning tone of 3500 Hz was added and presented concurrently with the stimulus for the duration of the latter (2 seconds a t 8 beeps per second) to reduce the possibility of a missed detection. Pilot performance measures and means of recording were identical to those in Part 1. The stimuli were similar to those used in Part I but were based upon a Cessna 150 model as opposed to the visually similar Cessna 177 used earlier (both single-engine, high-wing aircraft). Results
The intended scheme of analysis had not allowed for strategy differences between individuals. The discovery of such systematic differences in the data required a post hoc attempt to sort response patterns by type. Towards this end covariance between subjects was calculated. Two groups of nine subMethod jects each, arbitrarily labeled as Group A and Group B, positively covaried within groups Two independent variables, bearing and and negatively covaried between groups. (See collision index, were combined in the design. Beringer, 1976, for covariance table.) Six subNine bearing values which ranged from 20 jects remained unclassified. Of these six, only Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
HUMAN
534-0ctober, 1978
a single subject clearly used the collision index as as basis for his response. Because of the post-hoc allocation of subjects into groups, little detailed statistical analysis will be presented here. Examination of each group by analysis of variance was also impossible due to the appearance of zero variance in some cells after grouping. The results could be considered, however, using the plots of the obtained mean frequencies with plots of predicted mean frequencies (Figures 2 through 5 ) generated by the three plausible response strategies. Comparison w i t h response strategies. Plots of the obtained mean frequencies (equivalent to probabilities) for both groups by bearing and collision index appear in Figures 3 and 5, respectively. Comparisons of the predicted plots in Figure 2 with the obtained plots in Figure 3 indicate that the two groups may be characterized as attending to either bearing or aspect. Very close agreement was found between the regression equations for pre-
FACTORS
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Figure 3 . Mean frequency of a Left turn by group and bearing.
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Figure 2 . Predicted mean frequency of a left turn by response strategy and bearing.
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Figure 4. Predicted mean frequency of a lefi turn by response strategy and collision index.
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
D E N N I S B. BERINGER
October, 1978- 535
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SUMMARY AND CONCLUSIONS The results of Part I provide evidence that pilots and nonpilots exhibit different stereotypic behavior when confronted with a potential head-on collision; pilots generally turn right and nonpilots turn left. Earlier findings were replicated in that approximately 25% of the pilots having correct knowledge of the regulation preferred to turn left. Apparently the strength of the nonpilot response is such that present flight regulation training is insufficient to counteract fully this initial bias. The results of Part I1 indicated that for the particular conditions investigated processing of the target was usually performed on the basis of one of its two positional characteristics, bearing or aspect. In only one case was there any evidence of processing at the level of approach geometry (collision index). It is also clear that the use of a bearing-oriented strategy produces fewer reversals than a n aspect-oriented strategy. One possible explanation is that a conflict exists between bearing and aspect cues such that one interferes with responses based upon utilization of the other, and that the bearing cue is more immediate and salient. Two approaches based on response compatibility may be considered as solutions to the problem of response bias. “Inherent” compatibility uses the untrained response as the basis for judgment or criterion for equipment design. Prior pilot training and widespread control configuration usage reduce the likelihood that this approach could be used. The alternative solution is “trained response compatibility” where individuals are taught response patterns which coincide with existing rules. This is, in fact, the present state of affairs. It is possible that intensification of present training might produce a favorable
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Figure 5 . Mean frequency of a lefi turn by group and
collision index.
dicted performance and those for obtained performance (Beringer, 1976). No effect of collision index was evident. A comparison of Figures 4 and 5 suggests the same conclusion. Group A appeared to respond to aspect while Group B appeared to respond to bearing. Frequency of a left turn did not differ reliably between groups (p > 0.1) suggesting a difference of distribution only and not number. Reversals. A reversal was scored when a subject deviated bank angle by five degrees or more following a stimulus onset and then changed his response to the opposite direction prior to stimulus termination. Comparisons of groups by reversal frequency indicated a higher incidence of reversals for Group A. Group A exhibited 8 lefdright reversals and 26 rightlleft reversals while Group B
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
HUMAN
536-October, 1978
reduction in wrong-way responses. Knowledge of the strength of a n individual's initial bias could be used in this way to identify cases where additional or intensified training was warranted. The possibility of a return to initial response patterns during stressful situations, however, remains. ACKNOWLEDGMENTS This research, conducted at the Aviation Research Laboratory of the University of Illinois at UrbanaChampaign, received partial support from the Link Foundation. The author wishes to express his gratitude to the following individuals for their assistance during the course of the study: Stan Bengtson. Richard Haas, and John M i x for their technical assistance; Charles Lewis and Ledyard R. Tucker for their statistical advice: and Robert C. Williges and Jack A. Adams for their advising, editing of the thesis version, and endless patience.
REFERENCES Bates, M. R., Fletcher, H.K., Michnick, L., and Prast, J. W. History of time-frequency technology. f€EE Transactions on Aerospace and Ehctronic Systems. 1968 Vol. AES-4 (2), 238-256. Beringer, D. 8. Factors in collision avoidance response: Pilots and nonpilots. Unpublished undergraduate research study, University of California a t Los hgeles. 1971. Beringer, D. B.Collision avoidance response stereotypes in pilots and nonpilots. Savoy, Illinois: University of IIlinois at, Urbana-Champaign, Aviation Research Laboratory, TR ARL-76-6lLlNK-76-1, 1976. Crook, W. C . Pilot response to imminent collision threat. In Data Report on ProiectNo. 241-003-04X. Washington,
FACTORS
D.C.: Federal Aviation Administration, NAFEC Test and Evaluation Division, October, 1969. Crook, W.G. An investigation of the effect of relative motion on pilot judgments. In Data Report on Project No. 24140344X. Washington, D.C.: Federal Aviation Administration, NAFEC Test and Evaluation Division, October. 1970. Crook, W. G., Sulzer. R., and Hill. P. Aircraft avoidance maneuver rules for use with a pilot warning instrument. Washington, D.C.: Federal Aviation Administration, NAFEC, Report No. FAA-NA-72-22, 1972. Friedlander. G. D. At the crossroads in air-traffic control. I€€€ Spectrum, August, 1970. Graham, W. Human factors consideration in pilot warning instruments systems. Control Data Corporation. Report No. FAA-RD-71-114,December, 1971. Hanff, G. E. and Pessa. A. T. Collision avoidance visibility. Burbank, California: Lockheed-California Company, TR LR 19790-USTR #1004(SST). May 22,1966. National Transportation Safety Board. Midair collisions in U.S.civil aviation-1968. Washington, D.C.: National Transportation Safety Board. July. 1969. National Transportation Safety Board. Aircraft accident reports, brief format: U.S. Civil Aviation, 1974 accidents, Issues 1-5. Washington, D.C.: National Transportation Safety Board, NTSB,Report No. NTSB-BA74-4, 74-6, 14-7.75-2. 1975. Ross, H.L. Ignorance of collision course as a factor in traffic accidents. In J. S. Baker Experimental studies of traffic accidents. Evanston, Illinois: Northwestern University, Traffic Institute, 1960. Simpson. T. R.. Rucker, R. A., and Murray, J. P. Civil aviation midair collisions analysis: January 1964December 1971. McLean. Virginia: The Mitre Corporation, TR MRT-6334FM-EM-73-8, May, 1973. United States General Accounting Office. Report to the Congress: Aircraft Midair Collisions; A Continuing Problem. Washington, D.C.: General Accounting Office Report No. B-164497(1). October, 1974. Van Cott, H. P.and Kinkade, R. G. (Eds.) Human engineering guide to equipment design. Washington, D.C.: U.S. Government Printing Office, 1972, 556-559.
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
F A C T 0 RS, 1978,20(5), 529-536
Collision Avoidance Response Stereotypes in Pilots and Nonpilots DENNIS B. BERINGER', University o f Illinois at Urbana-Champaign
A two-part study was conducted to investigate the effects of target variables upon pilot and
nonpilot collision avoidance responses to simulated approaches which were head-on or nearly so. Part I investigated the effectof bearing and found that nonpilots preferred to turn lefi in a head-on approach.Although pilots generally turned right under the same conditions, 25% exhibited the nonpilot left-turn response. The nonpilot response bias seemed related to the type of control used for aircraft pilotage. Part I1 examined the effects of bearing and collision index (a geometric construct representing an index for optimal response selection) upon the responses of 24 pilots. Two subgroups were identified, one apparently attending primarily to bearing while the other attended to aspect. Only one subject appeared to use the optimal collision-index construct for response selection.
INTRODUCTION
The Pilot Task
A hazard encountered in present highThree sequential steps are necessary in the density air traffic operations is the mid-air maintenance of separation by visual means. collision. A summary of the incidents in 1968 These steps are detection, response selection, compiled by the National Transportation and response execution. Although much has Safeiy Board (NTSB,July 1969) indicated been done in the areas of target detection that such incidents were a real and present (Hanff and Pessa, 1966; Crook, 1970; Graham, danger while recent accident reports (NTSB, 1971) and response selection (Friedlander, 1974-1975,s volumes) indicate that the prob- 1970; Bates, Fletcher, Michnick, and Prast, lem persists despite many attempts to elimi- 1968) by machine systems, the prohibitive nate it. A general characterization of the costs of these systems (United States General mid-air collision drawn from the NTSB Accounting Office, 1974) greatly restrict their summary (Crook, Sulzer, and Hill, 1972, and use. For present purposes both adequate visSimpson, Rucker, and Murray, 1973) places ual detection and unaided response selection collision occurrences during operations will be assumed. where the pilot is responsible for maintaining Regulations have been structured (Federal adequate separation by visual means. It apAviation Regulations, Part 91.67) a n d pears necessary, then, to examine those tasks strategies developed (Crook, Sulzer, and Hill, which the piIot must perform to maintain 1972; Crook, 1969) to assist the unaided pilot this separation. in selecting appropriate maneuvers for maintaining separation. Beringer (1971) con' Requests for reprints should be sent to Mr. Dennis B. ducted a preliminary study involving the Beringer. Department of Psychology, University of Illinois at Urbana-Champaign,Champaign, Illinois 61820, U.S.A. Federal Aviation Regulation (FAR) governing Downloaded at Monash University on June 5, 2016 @ 1978.The Human Factors Society. Inc. from hfs.sagepub.com529 All rights reserved.
HUMAN
530-October, 1978
right of way in head-on or nearly head-on approaches. The regulation, believed derived from maritime law, requires both pilots to alter aircraft course to the right. The experiment, using a simulated auditory proximity warning indicator but no visual targets, revealed that one of every four licensed pilots examined turned left to avoid the instructionally defined head-on collision. The nonpilot response stereotype was a left turn, suggesting that the general population response interfered with selection of the FARspecified right turn by some pilots. Variables AffectingResponse
Two of the major classes of variables that influence the selection of a control response to an imminent collision threat are those affecting the appearance and position of the target (target variables) and those influencing pilot response skills (pilot variables). Although both hardware and environmental variables may also influence pilot behavior, the present discussion is restricted to the first two classes because they can be generalized across all mid-air encounters. Target variables. Although detection may be affected by target size, targedground contrast, location in the visual field, and target motion, Crook (1970) and Ross (1960) have emphasized that targets in collision approaches appear to have little or no motion relative to the observer. Thus, aspect and bearing appear to be prime variables for investigation. Aspeci can be thought of as variations in target appearance caused by rotating the target aircraft about its yaw (vertical) axis. In the absence of motion cues aspect should indicate the target's direction of travel. Bearing is the angle, in the horizontal plane, between thecenterlineof theobserver aircraft fuselage and a line connecting the target and observer. Although the pilot may not be seated on the fuselage centerline. the parallax is so slight for the distances involved that bearing may be measured from the aircraft centerline. Another observation of Crook (1969) showed that 40% of the mid-air collisions from 1964 through 1968 had convergence angles of
FACTORS
0 to IOdegrees(head-on)or 171 to 180degrees.This was confirmed in a larger sample by Simpson, Rucker. and Murray (1973). The range of values investigated, then, might be reduced to those within these limits.
Pilot variables. The prior experience which pilots have had with particular types of aircraft may result in negative transfer in some situations. Previously appropriate responses may become inappropriate or interfere with task performance. With this possibility in mind it is of interest to examine the flight histories of pilots with the intent of relating past experience to present performance. Purpose of Present Study
Utilization of the observations of Crook (1970). Ross (19601, Crook (19691, a n d Simpson et al. (1963) permitted a restriction of both the types and ranges of variables to be examined. Aspect and bearing should provide approach geometry information where no apparent target motion exists. Bearing values were restricted to those accounting for the majority of collisions. Aspect values were restricted to those which, in combination with the selected bearing values, would represent a reasonable collision threat configuration. Two phases of experimentation were designed to investigate the effects of these variables upon collision avoidance behavior. The first phase was intended to attempt confirmation of the nonpilot stereotypic response to head-on approaches as compared with that of trained pilots. The second phase was designed to evaluate the effects of selected values of bearing and aspect upon pilot collision avoidance behavior. PART I The first experiment was designed to examine pilot and nonpilot responses to head-on, or nearly so, collision approaches. This phase, using a motion-base simulator, visual targets, and a realistic flight task, served as an extension and elaboration of the earlier Beringer (1971) study.
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
DENNIS B. BERINGER
October, 1978-531
Method Three groups of 12 subjects each, composed of male nonpilots, female nonpilots, and male pilots respectively, were tested in a Link GAT-1 single-place flight training simulator. A rear projection system used with the simulator produced both a horizon and target images, Targets were white, positive-contrast aircraft silhouettes (Cessna 177) subtending two degrees of visual arc at zero degrees bearing. Although target bearing could assume any value from 355 degrees (five degrees left) to 005 degrees (five degrees right) in onedegree increments, target aspect was always head-on (zero). Both pilots and nonpilots were required to maintain the simulator in a level flight attitude with pitch and roll motion active while searching for aircraft targets. Subjects were required to execute an avoidance maneuver (turn) upon detection of an intruder aircraft, returning the simulator to Ievel flight upon disappearance of the target aircraft. Nonpilots received a short period of instruction, usually 15 to 20 minutes, in controlling the pitch and bank of the simulator. This instruction was sufficient t o give the subject adequate control over the simulator for the purposes of the experiment. Stimulus presentations were distributed such that five targets appeared at each bearing except zero degrees (centerline) where ten targets appeared. Repeated presentations generated a probability of lefthight turn over trials for each subject at each stimulus level. The targets appeared in a predetermined random order with randomly selected interstimulus intervals ranging from 8 through 14 seconds..Half of the center presentations were preceded by left-of-center targets and half by right-of-center targets. Although direction of turn was the dependent variable of primary interest as measured by recording bank angle, pitch angle was also
recorded by a two-channel paper strip chart ~. recorder. This allowed evaluation of preference for vertical components in the avoidance maneuver. A stimulus event marker indicated stimulus onset and offset. Previous pilot experience, hand preference, and eye dominance were assessed by means of a post-test questionnaire and interview. ResuZts A two-way analysis of variance was conducted on probability of a left turn by bearing and group membership. Effects of both bearing,F (10.330) = 7 5 . 4 7 , ~< 0.0001,and group membership, F(2,33) = 5.21, p < 0.01, were found to be significant. Scheffe post hoc comparisons at zero degrees bearing, a point of particular interest, showed no reliable difference between the male and female nonpilot groups (see Figure l), the females being more variable a s a group than the males. A similar comparison indicated that these two groups combined were reliably different from the pilot group ( p = 0.014). Nonpilot males and females had a higher median probability of turning left a t zero degrees bearing (0.80
,,oz a
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by haring
HUMAN
532-0ctober, 1978
and 0.60 respectively) than did the pilots (0.25). Three pilots, however, exhibited individual left-turn probabilities [ p (left)] at the centerpoint exceedingp(1eft) = 0.50, thus confirming Beringer's (1971) earlier finding which showed that 25% of the pilot population exhibited a left-turn bias. Neither reliable relationships between pilot experience and task performance nor reliable vertical deviation patterns appeared, although some pilots verbally expressed a preference for a climbing turn when interviewed afterwards. Discussion
Clearly, the stereotypic responses of nonpilots were quite different from those of pilots such that nonpilots preferred to turn left. The education of pilots according to the Federal Aviation Regulation requiring a right turn to avoid a head-on collision would appear to be less than 100% effective, because 25% of the pilots exhibited the typical nonpilot response. All the pilots in'this sample indicated a correct knowledge of the regulation in answering the post-test questionnaire. These pilots preferred to turn left even though they knew the regulation required the opposite response. Two questions arose subsequent to this investigation regarding the nonpilot stereotype. Perhaps the nonpilot bias could be attributed to some inherent motion tendency of the GAT-1 system. If not, a means of isolating the causal factor was desirable. Examination of the nonpilot responses to the questionnaire item asking if any differential ease of turn initiation had been noticed revealed no systematic bias to the responses. The fact that the stereotype was also observed in a simulation of a different type (Beringer, 1971) further suggested that the effect was not due to some systematic bias in the GAT-1. To clarify this question further a short investigation was then conducted outside the confines of the flight simulator to determine
FACTORS
whether the nonpilot bias was an internalized choice effect o r the result of a machinerelated factor. Twenty-four nonpilots, 12 male and 12 female, were presented the same forced-choice paradigm as that presented to subjects who operated the GAT-1. The PLAT0 1V computer display system was used for stimulus presentation and response recording. Subjects indicated response selection by single key presses when an aircraft target appeared on the plasma panel display. No systematic response bias was observed in this investigation. Restriction of the effect t o the flight simulators suggests that a characteristic common to both might be influencing response execution. The only characteristic common to both was the control yoke. It is not sufficient to say that flying with only the left hand on the yoke, as pilots do, makes the downward pull t o turn left the easier response because most nonpilots used both hands to manipulate the yoke. Anthropometric data (Van Cott and Kinkade, 1972)seem to suggest that more force can be exerted upward by the right hand on a vertical handgrip than b y the left hand, downward forces available being about equal. This would seem to favor the counterclockwise rotation for a left turn. Caution should be used in this approach, however, for as the elbow angle is decreased from 150 degrees to 90 degrees, the difference disappears. A similar argument may be developed for the stick configuration controller. PART I1 The second phase of experimentation was designed to examine the effects of bearing and aspect upon pilot selection of avoidance maneuver. Bearing and aspect were combined in a systematic manner to produce a new geometric construct called collision index (bearing minus aspect). This construct
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
October. 1978-533
DENNIS B. BERINGER
should provide an index of collision occurrence if both aircraft have approximately the same airspeed, a collision occurring when the value is equal to zero. It is plausible, then, that pilot response strategy could be based upon bearing, aspect, or collision index. Response Strategies Bearing. A strategy based upon bearing suggests that target location relative to the observer determines his response selection without consideration of target aspect. All bearings left of the visual centerline should cause a right-turn response [p(left) = 01;all bearings right of centerline should produce left turns [p(left) = 11. At a zero-degree bearing (head-on) the situation should prove ambiguous and result in p(1eft) = 0.5. Aspect. Processing in terms of target aspect suggests that for aspect values where the nose of the target aircraft is pointed to the observer’s left, p(1eft) = 0 should result. Values showing the nose to the right should produce p(1eft) = 1. A head-on aspect should produce p(1eft) = 0.5. Collision index. Evaluation of targets in terms of approach geometry, the collision index, would producep(1eft) = 0 for targets passing to the observer’s left and p(1eft) = 1 for targets passing to the right. The ambiguous case where collision index equaled zero should result in p(1eft) = 0.5. In this study collision index was assigned right and left labels such that it indicated in which direction the observer should turn, not the side to which the target would pass. Thus a target passing to the left would have a right collision index requiring a right turn.
degrees left of center to 20 degrees right of center were paired with seven values of collision index which ranged from 15 degrees left to 15 degrees right. Both covered their ranges by five-degree increments. Each combination of levels occurred once during the stimulus presentations with the exception of zerobearing-zero-collision-index. Nine presentations were added for this combination so that the data obtained a t this point could be directly compared with data obtained in Part I. Of the 24 pilots (22 males, 2 females) who participated, two were assigned to each of 12 stimulus presentation orders. Six of the orders were randomly generated with the remaining six being derivations of these random orders. The experimental task and instructions were essentially the same a s in Part I with minor revisions. A warning tone of 3500 Hz was added and presented concurrently with the stimulus for the duration of the latter (2 seconds a t 8 beeps per second) to reduce the possibility of a missed detection. Pilot performance measures and means of recording were identical to those in Part 1. The stimuli were similar to those used in Part I but were based upon a Cessna 150 model as opposed to the visually similar Cessna 177 used earlier (both single-engine, high-wing aircraft). Results
The intended scheme of analysis had not allowed for strategy differences between individuals. The discovery of such systematic differences in the data required a post hoc attempt to sort response patterns by type. Towards this end covariance between subjects was calculated. Two groups of nine subMethod jects each, arbitrarily labeled as Group A and Group B, positively covaried within groups Two independent variables, bearing and and negatively covaried between groups. (See collision index, were combined in the design. Beringer, 1976, for covariance table.) Six subNine bearing values which ranged from 20 jects remained unclassified. Of these six, only Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
HUMAN
534-0ctober, 1978
a single subject clearly used the collision index as as basis for his response. Because of the post-hoc allocation of subjects into groups, little detailed statistical analysis will be presented here. Examination of each group by analysis of variance was also impossible due to the appearance of zero variance in some cells after grouping. The results could be considered, however, using the plots of the obtained mean frequencies with plots of predicted mean frequencies (Figures 2 through 5 ) generated by the three plausible response strategies. Comparison w i t h response strategies. Plots of the obtained mean frequencies (equivalent to probabilities) for both groups by bearing and collision index appear in Figures 3 and 5, respectively. Comparisons of the predicted plots in Figure 2 with the obtained plots in Figure 3 indicate that the two groups may be characterized as attending to either bearing or aspect. Very close agreement was found between the regression equations for pre-
FACTORS
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Figure 4. Predicted mean frequency of a lefi turn by response strategy and collision index.
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
D E N N I S B. BERINGER
October, 1978- 535
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SUMMARY AND CONCLUSIONS The results of Part I provide evidence that pilots and nonpilots exhibit different stereotypic behavior when confronted with a potential head-on collision; pilots generally turn right and nonpilots turn left. Earlier findings were replicated in that approximately 25% of the pilots having correct knowledge of the regulation preferred to turn left. Apparently the strength of the nonpilot response is such that present flight regulation training is insufficient to counteract fully this initial bias. The results of Part I1 indicated that for the particular conditions investigated processing of the target was usually performed on the basis of one of its two positional characteristics, bearing or aspect. In only one case was there any evidence of processing at the level of approach geometry (collision index). It is also clear that the use of a bearing-oriented strategy produces fewer reversals than a n aspect-oriented strategy. One possible explanation is that a conflict exists between bearing and aspect cues such that one interferes with responses based upon utilization of the other, and that the bearing cue is more immediate and salient. Two approaches based on response compatibility may be considered as solutions to the problem of response bias. “Inherent” compatibility uses the untrained response as the basis for judgment or criterion for equipment design. Prior pilot training and widespread control configuration usage reduce the likelihood that this approach could be used. The alternative solution is “trained response compatibility” where individuals are taught response patterns which coincide with existing rules. This is, in fact, the present state of affairs. It is possible that intensification of present training might produce a favorable
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dicted performance and those for obtained performance (Beringer, 1976). No effect of collision index was evident. A comparison of Figures 4 and 5 suggests the same conclusion. Group A appeared to respond to aspect while Group B appeared to respond to bearing. Frequency of a left turn did not differ reliably between groups (p > 0.1) suggesting a difference of distribution only and not number. Reversals. A reversal was scored when a subject deviated bank angle by five degrees or more following a stimulus onset and then changed his response to the opposite direction prior to stimulus termination. Comparisons of groups by reversal frequency indicated a higher incidence of reversals for Group A. Group A exhibited 8 lefdright reversals and 26 rightlleft reversals while Group B
Downloaded from hfs.sagepub.com at Monash University on June 5, 2016
HUMAN
536-October, 1978
reduction in wrong-way responses. Knowledge of the strength of a n individual's initial bias could be used in this way to identify cases where additional or intensified training was warranted. The possibility of a return to initial response patterns during stressful situations, however, remains. ACKNOWLEDGMENTS This research, conducted at the Aviation Research Laboratory of the University of Illinois at UrbanaChampaign, received partial support from the Link Foundation. The author wishes to express his gratitude to the following individuals for their assistance during the course of the study: Stan Bengtson. Richard Haas, and John M i x for their technical assistance; Charles Lewis and Ledyard R. Tucker for their statistical advice: and Robert C. Williges and Jack A. Adams for their advising, editing of the thesis version, and endless patience.
REFERENCES Bates, M. R., Fletcher, H.K., Michnick, L., and Prast, J. W. History of time-frequency technology. f€EE Transactions on Aerospace and Ehctronic Systems. 1968 Vol. AES-4 (2), 238-256. Beringer, D. 8. Factors in collision avoidance response: Pilots and nonpilots. Unpublished undergraduate research study, University of California a t Los hgeles. 1971. Beringer, D. B.Collision avoidance response stereotypes in pilots and nonpilots. Savoy, Illinois: University of IIlinois at, Urbana-Champaign, Aviation Research Laboratory, TR ARL-76-6lLlNK-76-1, 1976. Crook, W. C . Pilot response to imminent collision threat. In Data Report on ProiectNo. 241-003-04X. Washington,
FACTORS
D.C.: Federal Aviation Administration, NAFEC Test and Evaluation Division, October, 1969. Crook, W.G. An investigation of the effect of relative motion on pilot judgments. In Data Report on Project No. 24140344X. Washington, D.C.: Federal Aviation Administration, NAFEC Test and Evaluation Division, October. 1970. Crook, W. G., Sulzer. R., and Hill. P. Aircraft avoidance maneuver rules for use with a pilot warning instrument. Washington, D.C.: Federal Aviation Administration, NAFEC, Report No. FAA-NA-72-22, 1972. Friedlander. G. D. At the crossroads in air-traffic control. I€€€ Spectrum, August, 1970. Graham, W. Human factors consideration in pilot warning instruments systems. Control Data Corporation. Report No. FAA-RD-71-114,December, 1971. Hanff, G. E. and Pessa. A. T. Collision avoidance visibility. Burbank, California: Lockheed-California Company, TR LR 19790-USTR #1004(SST). May 22,1966. National Transportation Safety Board. Midair collisions in U.S.civil aviation-1968. Washington, D.C.: National Transportation Safety Board. July. 1969. National Transportation Safety Board. Aircraft accident reports, brief format: U.S. Civil Aviation, 1974 accidents, Issues 1-5. Washington, D.C.: National Transportation Safety Board, NTSB,Report No. NTSB-BA74-4, 74-6, 14-7.75-2. 1975. Ross, H.L. Ignorance of collision course as a factor in traffic accidents. In J. S. Baker Experimental studies of traffic accidents. Evanston, Illinois: Northwestern University, Traffic Institute, 1960. Simpson. T. R.. Rucker, R. A., and Murray, J. P. Civil aviation midair collisions analysis: January 1964December 1971. McLean. Virginia: The Mitre Corporation, TR MRT-6334FM-EM-73-8, May, 1973. United States General Accounting Office. Report to the Congress: Aircraft Midair Collisions; A Continuing Problem. Washington, D.C.: General Accounting Office Report No. B-164497(1). October, 1974. Van Cott, H. P.and Kinkade, R. G. (Eds.) Human engineering guide to equipment design. Washington, D.C.: U.S. Government Printing Office, 1972, 556-559.
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