Proposing Attitude Indicator Modifications to Aid in Unusual Attitude Recovery

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International Symposium on Aviation International Symposium on Aviation Psychology - 2009 Psychology

2009

Proposing Attitude Indicator Modifications ot Aid in Unusual Attitude Recovery

Nathan B. Maertens

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Repository Citation Maertens, N. B. (2009). Proposing Attitude Indicator Modifications ot Aid in Unusual Attitude Recovery. 2009 International Symposium on Aviation Psychology, 349-354. https://corescholar.libraries.wright.edu/isap_2009/57

This Article is brought to you for free and open access by the International Symposium on Aviation Psychology at CORE Scholar. It has been accepted for inclusion in International Symposium on Aviation Psychology - 2009 by an authorized administrator of CORE Scholar. For more information, please contact [email protected]. PROPOSING ATTITUDE INDICATOR MODIFICATIONS TO AID IN UNUSUAL ATTITUDE RECOVERY

Nathan B. Maertens University of Illinois at Urbana-Champaign Savoy, Illinois

Pilots’ inability to recover from unusual attitudes (UA) is a major factor in loss of control in-flight (LOCIF) accidents, the largest cause of commercial aviation fatalities (Boeing, 2008). One study found 58% of professional pilots and 72% of general aviation pilots were unable to recover from LOCIF upsets (Regional Aviation News, 2008). Statistics also show that LOCIF is the only fatal aviation accident type not to appreciably decrease over a 21 year period ending in 2002 (Sumwalt, 2003a). A revision of the attitude indicator (AI) is proposed to examine if this would reduce the problem by keeping pilots from flying into UA, accelerate UA identification and enhance recovery. The proposed modifications are: add triangles filled with graduated colors to indicate horizon position, roll and pitch indicators that inform pilots of UAs and corrective procedures, and a thrust indicator that indicates throttle action to maintain adequate energy for aircraft recovery.

Loss of control in-flight (LOCIF) is the primary cause of worldwide aviation fatalities. A LOCIF is classified as a failure or an inability to get an aircraft’s wings level and usually results from an unusual attitude (UA) (Schlimm, 2005). An UA condition is defined as greater than 45o bank, 25o pitch up, 10o pitch down or flying at speeds inappropriate for conditions while within the above parameters (Sumwalt, 2003a). Failure to recognize and promptly recover from such an UA can easily result in a plane crash. Over the ten year span from 1998-2007 LOCIF resulted in the greatest number of aviation fatalities for the commercial jet fleet, 22 fatal accidents and 2051 lives lost (Boeing, 2008). For corporate aircraft accident data from 1982 to 2002 LOCIF is the only mishap type that had not appreciably decreased (Sumwalt, 2003a). General aviation (GA) numbers are equally dismal. In 2000, there were 261 GA LOCIF accidents, 111 of these were fatal with 179 lives lost (NTSB, 2001). This accounted for 14% of all GA mishaps that year. 2001 saw 233 mishaps from LOCIF, 13% of all mishaps that year (NTSB, 2002). Although the LOCIF rate went down slightly, it still caused 111 fatal crashes with 190 lives lost. These numbers have not improved; in 2005 18% of all fatal GA accidents were due to a LOCIF (FAA, 2006). Several studies have examined how well certification requirements ensure that pilots are capable of recovering from an UA. According to one study 58% of professional pilots and nearly 72% of general aviation pilots were unable to recover from LOCIF upsets (Regional Aviation News, 2008). "As evidenced by our research results, pilots are ill-equipped to deal with loss of control scenarios beyond the accepted limitations of their training requirements during pilot certification and recurrent simulator training” (Regional Aviation News, 2008, p. 1). Another study corroborated these findings by noting that unusual attitude recovery training for commercial pilots was inadequate (Gawron, Berman, Dimuskes and Peer, 2003). In particular, it was noted that the stress of the unexpected scenario as well as the demand for immediate and correct analysis of the situation and correct action were overwhelming for many of their participants, directly inhibiting their ability to recover the aircraft. According to a director of flight operations for a major U.S. based carrier another key skill that has been reported missing from the aviation industry’s efforts to reduce LOCIF is training pilots to be able to “recognize potential upset conditions” (Sumwalt, 2003b, p 14). Unfortunately, one of the primary instruments designed for pilot orientation, the attitude indicator (AI), has been indicted as part of the problem. Numerous studies have shown that the western AI variant may lead to pilot misinterpretation and subsequently a recovery in the incorrect direction, complicating the problem and robbing the pilot of precious time. This situation is known as a roll reversal. Interestingly, the Soviet AI variant utilizes a different display type and has been shown in multiple studies to be more intuitive and less likely to induce roll reversals (Previc and Ercoline, 2000). LOCIF consistently costs hundreds of lives and millions of dollars annually. Something must be done to help improve pilots’ abilities to recover from UA and prevent these disasters. Some of this problem can be attributed to pilot disorientation, some to instrument misinterpretation and some to pilots failing to identify the developing situation. This paper proposes a comprehensive and intuitive solution to this problem by improving pilot awareness of developing aircraft attitude problems, reducing the opportunity to misinterpret their instruments, providing guidance for an expeditious recovery and in accomplishing these objectives reduce the threat of loss of control in-flight.

349 Proposed Solution

The solution proposed is to make modifications to the AI that will help improve its interpretation and have it provide corrective guidance in throttle settings as well as in the roll and pitch directions. Three specific modifications are being proposed: a horizon indicator that improves ability to discern horizon location, roll and pitch guidance and throttle guidance. These modifications should be compared with both the Western and Soviet AI displays to determine which combination improves performance best.

Horizon Indicator

The horizon indicator is designed to help pilots more readily discern the horizon’s location. Isosceles triangles drawn into the ground and sky of the AI can meet this goal. The apices of these triangles would meet at the horizon line to form an hour glass with their opposing lines residing on their respective 90o pitch lines. To further elucidate horizon location the inside of the triangles would be colored with a gradient that is dark near the 90o pitch lines but pale near the horizon line. In this way, regardless of the orientation displayed on the AI, the pilot will always be able to discern the horizon location by following the visible triangle’s contours and color gradient to its apex. This intervention seeks to mitigate conditions such as seen in Figure 2 where no horizon line is evident, which can easily lead to a roll reversal.

Figure 1. Horizon indicator Figure 2. Extreme unusual Figure 3. Extreme unusual at horizon. attitude without horizon attitude with horizon indicator. indicator.

Roll and Pitch Indicator

The second modification is to add roll and pitch correction indicators. Roll and pitch correction indicators would flank the perimeter of the AI (Figure 4). These indicators would illuminate with a green hue in the direction of correction necessary to recover to straight and level flight. These indicators are designed to illuminate to improve their salience. Not only do they instruct a pilot of correct recovery inputs but also promptly raise awareness of a hazardous situation as it develops, thereby compensating for the cognitive deficit experienced by a task saturated, complacent or distracted pilot.

Figure 4. Roll and pitch indicators commanding a right bank and a pull up.

To prevent human misuse of automation (e.g., overtrust) these indicators would only illuminate when the aircraft attitude is approaching a situation that could devolve into danger. Should the pilot fail to recognize these warnings and the attitude become worse, the appropriate roll and pitch indicators would blink to further increase their salience. The turn off threshold should be set at a value less than the turn-on threshold. This gap would prevent issues where a pilot flying on the cusp of the roll indicator’s

350 illumination settings would cue the indicator to turn on and off with slight changes in bank. This type of situation could lead to a detriment in safe flight performance as it might result in annoyance, distraction or complacency. Another item to be considered with the roll guidance indicators is an inverted attitude. In this situation the wings would be straight and level so the bank indicators would not be illuminated. This could be extremely dangerous because if the plane concurrently had a nose low attitude the pilot’s roll and pitch indicators would instruct the pilot to pull back on the controls—in effect complicating the situation and flying the aircraft to the ground. To prevent this, the system could be programmed to account for inversions. Should an inversion occur the roll indicators should instruct the pilot to recover to the right because people are biased toward this direction (Wickens, personal communication, September 9, 2008).

Throttle Guidance Indicator

The first two modifications were designed to help pilots more easily interpret their AI and provide guidance to recover to straight and level flight. The final modification examines another key aspect of aircraft control and unusual attitude recovery—the energy state. An attempt to correct an unusual attitude without attending to the current energy state may stall the aircraft, exacerbating the situation. The throttle guidance indicator was designed to assess the aircraft’s total energy state and make recommendations on whether more or less throttle input is necessary to recover the aircraft (Figures 5 and 6). To prevent automation misuse the throttle indicator should only be active when the roll and pitch indicators are illuminated. The throttle indicator would be displayed off-center of the AI and move vertically to indicate necessary changes in throttle setting. This display would be high on the AI if the system should decrease its energy (Figure 5); conversely, if an increase in energy state is warranted the indicator would be low on the AI (Figure 6). If the aircraft has the appropriate amount of energy the display would be in the vertical center of the display and covered by the aircraft watermark and 900 bank lines; and thus, not be visible when unnecessary.

Figure 5. Throttle guidance indicator prompting Figure 6. Throttle guidance indicator prompting a decrease in energy state. an increase in energy state.

Theoretical Foundations

Psychological Display Dynamics

First, it should be discussed why visual symbols should be used rather than alternatives (e.g. auditory or tactile recovery cues). Visual information is placed into the visuospatial sketchpad of spatial working memory which people use to help them in mental manipulation, recalling items they see and executing actions (Wickens and Hollands, 2000). In an unusual attitude the pilot is trying to control the aircraft and make the AI “read right,” spatial working memory activities; therefore, it is wholly appropriate that the display be pictorial. Additionally, accuracy and speed of recognition is greatest if displayed stimuli are presented in a format commensurate with the unit in memory’s representation, indicating that a pictorial display should also accelerate recovery (Wickens and Hollands, 2000). Abiding by the proximity- compatibility principle and co-locating information on energy state, roll and pitch information may also accelerate recovery and ease the effort of an instrument scan. Lastly, in time constrained situations with high cognitive demand, such as an unusual attitude recovery, a command display can be best as they save pilots one extra processing step, thereby accelerating response and reducing error rates (Wickens and Hollands, 2000). This is why the roll, pitch and throttle indicators were chosen to be command displays.

351

AI Display Type

The discussion of superiority between the Western and Soviet AI has been examined for decades. Previc and Ercoline (2000) conducted a thorough analysis of this literature and made an extremely convincing argument of the superiority of the Soviet display. The Soviet display presents an aircraft symbol that banks right and left against a vertically moving background. This display type is known as an outside-in (O-I) display because it is similar to what an individual outside of an aircraft would see looking at an aircraft. The Western display holds the aircraft stationary and the world shifts. This display is conformal to what a pilot in an aircraft would see when looking out at the horizon and is hence known as an inside-out (I-O) display. Problems with the I-O display center around the fact that people have a tendency to control the moving part and hence enter control inputs based on the world’s motion, not the aircraft’s— exactly opposite that which is appropriate, leading to roll reversals. It would be interesting to see if the I-O display with these modifications can outperform the O-I display or if the O-I display would be even further enhanced with these modifications.

Horizon Indicator

The primary advantage of the horizon indicator is that the triangles always point toward the horizon and the triangle embedded in the ground always points in the direction (i.e. left or right) in which the controls must be moved to regain level flight from a bank. The color gradient further supports this by capitalizing on the innate human perception of aerial perspective—as objects get further away their color becomes bluer and paler. This is not the first time that such a modification has been evaluated. Liggett, Reising and Hartsock (1992) attempted this in their background attitude indicator display, except they used a wedge rather than a triangle. Pilots performed best when color shading with a trapezoid pointing to the horizon was used. They theorized that this finding was commensurate with the concept of optical flow fields—their color shading and wedge pattern both functioned to direct the pilot back to the horizon. These cues were thought to be perceived without the necessity of much information processing. In their study they found that pitch lines broke up some of the optical flow and that numbers next to the pitch lines further slowed the pilot’s interpretation of the display. In further discussion of this experiment Liggett, Reising and Hartsock (2000) noted a significant double interaction between the wedge and pitch lines with numbers when color shading was present. However, the delay in reaction time, 42msec, was not deemed practically significant by participant matter experts. Furthermore, the pilots were found to prefer the pitch lines with numbers despite their lack of performance enhancement (Liggett, et. al., 2000). Due to preference, the importance of pitch lines and their numbers in indicating absolute orientation and the negligible practical impact on performance, pitch lines and their numbers should be incorporated with this horizon indicator.

Roll and Pitch Guidance Indicator

The roll and pitch indicators were intentionally selected to illuminate on the side in which correction would be necessary rather than on which side they are over-banked/pitched. Research on the Simon effect has shown that stimuli presented to the left or right of a fixation, when stimulus location is irrelevant (i.e., color is the cue), results in faster response if the stimulus location coincides with the assigned response’s location (Proctor, Lu, Van Zandt, 1992). Proctor, et. al. also found that response precuing enhances this effect. Although the Simon effect typically discusses horizontal responses, due to a right-left dimensional preference, the Simon effect also works in the vertical direction as well (Proctor, Vu, Nicoletti, 2003). This right-left preference actually serves pilots well as it helps them correct their roll prior to their pitch which is typically appropriate in unusual attitude recovery. Additionally, this display-action compatibility noted by the Simon effect corresponds to performance standards found in instruments with which pilots are already familiar (e.g. instrument landing system needles). The effectiveness of peripheral cuing for flight guidance during instrument approaches was demonstrated by Hasbrook and Young (1968). In their study they placed peripheral light cues on the yoke of the aircraft that would indicate if the aircraft orientation had strayed greater than 1.5 degrees from straight and level flight. As the magnitude of deviation increased the light cues would blink more rapidly and transition from green to red to provide situational feedback and improve their salience. In this study it

352 was specifically noted that pilots maintained straight and level flight 35% more frequently with solely peripheral cuing (no visible attitude indicator) than they did with their regular instruments. Hasbrook, et. al. credit this to the fact that pilots were able to recognize and correct for their banked situation by peripheral cues even if they were not looking at the attitude indicator. Peripheral cueing resulted in a statistically significant (p< .01) improvement in unusual bank attitude corrections and no roll reversals; whereas 30% of the participants with their regular attitude indicator had a roll reversal.

Throttle indicator

The movement of the throttle indicator was specifically designed to correspond with the principle of the moving part—“the direction of movement of an indicator on a display should be compatible with the direction of physical movement and the operator’s mental model” (Wickens and Hollands, 2000, p. 135). If there is too much energy in the system the pilot would need to pull back on the throttle. This movement of the throttle directly correlates to the throttle indicator moving down on the AI. Adhering to this principle makes the system intuitive and hence more beneficial to the user in cognitively demanding situations, such as unusual attitude recovery.

Summary

This paper sought to propose some modifications to the current attitude indicator used in airframes to help improve safety rates by reducing loss of control in-flight mishaps. Three modifications were proposed: a horizon indicator, roll and pitch guidance indicators and throttle guidance indicators. These modifications were specifically designed to capitalize on multiple experimentally proven concepts to provide better information to the pilot in the dire situation of an unusual attitude. Examining these display types with both the conventional I-O and Soviet O-I attitude indicators may improve pilot performance in preventing, identifying and recovering from unusual attitudes and should be conducted.

Acknowledgments

The genesis for the roll and pitch corrective indicators spawned from the SD command indicator from Small, Fisher, Keller and Wickens (2005) and Wickens, Self, Andre, Reynolds and Small (2007). The idea for the throttle indicator was inspired by the work done by Amelink, Mulder, van Paassen and Flach (2005) in looking at total energy maintenance for aircraft on approach to landing. I would like to thank several people for help in developing this project: Don Talleur for his expertise and guidance with respect to flying and recovery procedures. Ashwin Jadhav for his assistance in translating several Russian articles on attitude indicators and also his aeronautical engineering expertise in developing the throttle indicator. Jonathan Sivier for his help in drawing the illustrations in the figures and in programming an experiment to test these displays. Lastly, my advisor, Terry von Thaden in helping me flesh out these ideas. The views expressed in this article are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government.

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