Ringo Schmelzer

Keywords: Automation, Cockpit displays, Human factors, human-machine interface,

situation awareness, Glass-cockpit, Head up Display, miss-match, Cockpit Traffic Displays (CDTI)

Pilots learn to fly and study the systems of an airplane. They have to be aware of the situation, the controls, panels and displays all time. The human-machine interaction is the key issue to maintain safety and create situational awareness. The good coupling between human cognitive capabilities and the machine can help to defy problems. As an example, the amount of time the pilot’s head is down to monitor displays could be reduced by improvements of the design.

The computer interface and the information flow between the pilot of a modern civil aircraft and the cockpit display panel are a critical issue to assure flight safety and to make progress in civil aviation technology. To emphasize the meaning of the safety issue, which is dependent on the one hand from a technological standpoint and on the other hand from the capability, awareness, knowledge and experience of the pilot, I would like to give a preliminary example.

Several years ago an aircraft with German passengers on board was about to depart from the Dominican islands and bring the passengers back to their home country from their Christmas vacation. On the runway, the aircraft was already accelerating, the pilot recognized a problem with his velocity display. In this case, the velocity of the aircraft was lower than the critical lift-off velocity, instead of bringing the aircraft to a full stop the pilot decided to go ahead. The aircraft had its lift-off and the autopilot, which itself received the wrong information, was engaged. During the climb the autopilot increased the pitch by using the trim ruder of the tale elevator, which caused the aircraft to decelerate. Finally, the pilot decided to take control of the aircraft by disconnecting the autopilot. However, he did exactly the same thing as the autopilot before. By putting too much attention on the information given by the erroneous velocity value, he further increased the flight pitch, which was a wrong decision. Additionally he reduced the throttle, which caused the aircraft to stall. He lost control of the aircraft and the plane crashed into the water, the result being the loss of roughly 200 lives.

Ironically, at all stages up to the phase where the aircraft engine went off, the accident could have been prevented. The displays and instrument within the aircraft are redundant. The displays on the co-pilot side worked well and showed the correct velocity. Beside a communication problem and hierarchical problems, it was a Turkish airline, presumably the pilot lost the awareness of his aircraft. He made the wrong decisions. What causes the loss of awareness? Could accidents like this be prevented if there was more information offered or in a better manner? Is there a lack of training? Does there exist a lack of information on what is behind the displays?

However, the story reflects the lack of flight situation awareness and wrong decision making of the pilot caused by an error in the velocity-measuring gauge, cognitive work overload and wrong information provided by the flight computer.

In aircrafts nowadays the pilot functions as an observer who monitors the displays and information from the flight computer, pays attention to the environment and has to concentrate on communication tasks. To facilitate the amount of work and tasks he has to accomplish, the aircraft becomes more and more computerized. Flight modes take over the actual pilot work and flight responsibility, but the highest authority remains with the pilot. He can interact and interrupt an autopilot mode whenever it is necessary to take control. Consider that this requires information about the flight mode he is currently engaged in. The technological evolution led to the establishment of the glass-cockpit and within this evolution the role of design and ergonomics becomes increasingly important. To attain improvement the cockpit has to be centered and designed around the pilot, which refers to the user-centered design. (Wickens, 1997)

To back this up the following numbers taken out of a survey of the German Pilot Association emphasize the need for glass-cockpit modification. The survey reveals that 67 percent of the pilots asked felt occasionally overloaded with visual information. While 31 percent of the pilots who fly conventional cockpits said that they would like a higher degree of sensation, this number increases to 42 percent among the pilots flying an older generation of glass-cockpits. Whereas 65 percent of the pilots flying the most modern aircraft cockpit used in Airbus A320/321,A330/340 asked for improvements in this area. Interestingly, 71 percent of the pilots would appreciate an increase in usage of acoustical information as an additional sensory source of information. Also worth mentioning is that the basic setup of the cockpit design does not show remarkable differences unlike the assumption that an improvement in display technology also implies an improvement in cockpit design.

The survey also reveals the alarming information that 56 percent of the pilots with second generation glass-cockpits considered the material mediated in training to be unsatisfactory plus the quantity of the material is below satisfactory. Another 80 percent of the glass-cockpit pilots admitted that they ask themselves occasionally "What is the system doing now?". Finally, the survey draws the conclusion that the current competency and definition of the pilot’s role does not conform to the new cockpit technology. "The current procedures in aircraft manufacturing are by far not up to the requirements". Beside this conclusion, the survey reflects a good fundamental approach to improvement in cockpit design (Burgner, 5/97). The pilots demand for acoustical information enhancement, reduction of graphical information overload plus support with the necessary background information of new cockpit interfaces and training refers to the basics of Donald Normans designing rules (Norman, 1990). This will be discussed later in this paper.

This paper tries to discuss human cognition and sensory perception in interaction with the cockpit displays. Therefore, the focus will be on display design and auditory signal support. This refers to the human-machine interface problem within the human factors engineering discipline. To reduce the broad range of problems that occur with this topic. Concerning the issue of threads to safety, resulting from spatial disorientation and loss of situational awareness, it is required to introduce two cognitive principles, which are namely spatial disorientation (SD) and Loss of Situational Awareness (LSA). Both of these concepts are not easy to define. Both involve a lack of awareness and problems with matching the mental model to the information presented by the environment. This can result in misunderstandings and wrong predictions (Boers, 1996/97). SD stands for erroneous sense of position, heading and speed relatively to the earth’s surface (Mortimer, 1995). LSA is related to SD, but confuses more environmental aspects including geographical position aspects (Mortimer, 1995).

This paper tries to discuss possibilities of cockpit display design that make recommendations to enhance safety and increase situational awareness.

The discussion starts with the question of how much information is needed to accomplish the flight task and get support in dangerous situations where background information would be appropriate. In conformance to Wickens and the survey mentioned above, an overload of information, which has to be perceived visually, can lead to confusion and distraction from the information perception demanded to accomplish a task. Likewise, different events have different information values. Thus, it’s worth researching which kinds of information have to be conveyed most often in regular flight operation and during special events occurring. System design can shift performance along the bandwidth dimension. Bandwidth is a measure of efficiency introduced by Wickens to make different designs comparable among each other. An increase of bandwidth reaction speed and accuracy will increase in performance too. This is due to properties of the sensory apparatus.

To consider the cognitive capabilities of the pilot a feature analysis should be undertaken. The stimulus of the outside world has an impact on the cognitive process of the human brain. To increase the efficiency of this process the information presented by the cockpit interface is the vulnerable aspect. Feature analysis includes breaking the stimulus into component features matching the components into the long-term memory and deciding, which is the best match. It is important to understand what the information means. This implies that the conceptual model of the pilot has to be compatible with the information provided by the design. The display has to be compatible with the cognitive organization. In addition, it is important to consider that cues to identification are context and familiarity. To use this on auditory information it is better to provide information within the context. "Aircraft is in altitude capturing mode" is better than "altitude capturing on". Keywords like "mode" and "aircraft" create a better image in the memory of the pilot, which enables him to keep situational awareness.

Visual displays should be arranged in a way to reduce information access costs. Displays and panels must be scanned frequently and searched for relevant information. The reaction time can be a crucial issue. Within an emergency situation it is important to react as quickly as possible. To support the monitoring and emergency reaction task the principles based on attention should be applied here. Thus, besides minimizing the information access costs, the proximity and multiple recourses principles are appropriate (Wickens, 1997). Modern aircraft displays provide a large amount of displayed information. To attract certain values the "pop-out" effect can be applied. That means that a signal can be localized independently among a large variety of other values by changing the contrast or flickering the critical value on the display, which could be done with a rapid change in the luminance. Simply changing the color would not lead to a positive effect and the application is useless for this purpose. But colors regularly used on displays allow a rapid localization and can be used to organize the display. For example a hierarchy in importance among the values provided by the flight computer. (Wickens, 1997)

Three-dimensional displays can be helpful for situational awareness, but it also includes a certain amount of ambiguity. This is grounded in a better experience with the top view mapping. And a quicker realization of directions is possible. Therefore 3-dimensional displays application is less favorable. A possible application could be the use of 3-dimensional displays in connection with 3-dimensional ground surface simulation. An example would be an aircraft approaching an airport runway under bad weather conditions. The pilots task to monitor instruments and processing the landing maneuver could require all of his cognitive potential. Under this poor environmental conditions the occurrence of a system error could lead to a work overload the pilot has to fulfill. The simulation of the airplane flying on the glide path and the visualization of the surface by a computer could facilitate the monitoring process, when the environment is clearly visible. Another advantage is the increase in flight safety based on the ability to make other aircraft, aloft visible. The pilot can search for possible threats from the environment. But in this case it is arguable if this system should be integrated head down or in a head mounted display system. The possibility of an increase in situational awareness has to be evaluated for possible usage.

The next paragraph discusses the application of head-up-displays (HUD). HUD’s were developed and are used for military purposes. The major advantage is that the pilot doesn’t need to look down to obtain information. He can keep his eyes straightforward. The ‘head-up-display’ projects the most important data in front of the windshield. The projection is focused at infinity so the pilot does not have to accommodate his eyes to read this information in detail. The direct environmental contact is maintained. Therefore, the HUD-display offers possibilities to enhance flight safety. However, there is also a downside. The information presented can mask events and objects outside of the pilots cockpits by overlapping imagery (Wickens, 1997). Also the information presented can become cluttered. That can result in attention problems and decrease in performance. A suggestion is to use different light intensities and colors. Another big advantage is the possibility to conform shapes, like the shape of a runway. Also, the principles of pictorial realism; moving parts and ecological interfaces can be exploited to fully utilize the potential embedded in HUD-displays. Examples for this are the moving arrow in vertical direction to show the velocity and the moving arrow in horizontal direction used to determine the heading of the aircraft. According to accidents that happened by mixing up the aircraft pitch with the vertical speed the HUD-display offers the alternative of projecting the pitch and the vertical speed in different symbols. While the pitch is depicted in the form of vertical lines that move up and down, the vertical speed can be depicted in the form of up and down arrows plus the rate of change in altitude by numbers.

As described in the introduction, pilots demand the use of more auditory information. Auditory and visual perception occupy different regions of the cognitive brainwork. Many accidents happen while the pilot is under heavy visual workload. Therefore it has to be discussed whether the use of auditory systems could be suitable or not for flight information spread. Despite the visual system, the auditory system does not require direct attention to a certain direction to perceive stimuli. There is no need to scan a display or to search for a certain value. Auditory stimuli have the advantage of attracting attention immediately. The danger of trusting in auditory signals lies in false interpretation or wrong understanding of what was emitted. Also, one has to consider that most communication within the cockpit is auditory. Thus, two auditory information sources at the same time could lead to confusion and distracting. Another problem is to match the auditory information, which is of more value for the operator. That is the reason why designers prefer to apply auditory information only in emergency situations. An operator under stress can become over-aroused when presented with extra auditive signals, causing performance to deteriorate (Wickens, 1997). More useful can be the application of spatialized auditory head-up displays. By using the 3D possibilities, the sound can come from any given position. This allows the pilot to stay focused in his view outside the window. The spatialized auditory HUD displays could also help visual search. The application of auditory displays can be used to enhance aerospace safety and situational awareness.

The number of systems, modes and the complexity of the aircraft has increased in the recent years. Automation should lead to reduction of the pilot workload. The capability of the human brain and the limitations to process the information transmitted by the system has to be considered. The amount of information transmitted and measured in bits can be unlimited. Unlike this, the capacity of the human brain only enables processing of a few bits of information. If a difference between the amount of information transmitted and the capability of what can be processed occurs, a miss–match between pilot and cockpit information system may be the result (Lovesey, 1995). As a recommendation one can subsume that too much information presentation should be avoided. Furthermore, the pilot perception diminishes if there are environmental sources like noise or bad weather conditions distracting the pilot. During the flight the information necessary to complete a flight mission must be chosen to be presented in the right time either by the pilot him/herself or the system automatically (Lovesey, 1995).

To ensure an adequate information process regarding the human cognitive work and avoiding miss-matches, Lovesey lists some points of recommendations that could be incorporated into future aircraft systems. He suggests the reduction of information overload towards the operator, avoiding unnecessary information and attempting to submit all calculations to the aircraft computer. The latter argument refers especially to smaller commuter aircraft, in which the information displays and flight computers are not so progressive as in modern civil aviation airplanes, where the flight computer does almost do all calculations. Beside this, he suggests avoiding uninteresting and repetitive tasks. Furthermore, the pilot should work on tasks that he enjoys, this resulting in more attention being paid and maintains situational awareness by giving him enough work to occupy himself but leaving enough mental capacity to deal with emergency cases.

Another list of human factors issues gives further recommendations. The pilot is the person around whom the cockpit has to be designed. This refers to the pilot centered design, in which designers should focus on pilot requirements. Therefore the information requirements have to be defined clearly. Consideration of interdependence between the pilot information requirements within a flight situation has to be taken into account. Attention-sensitive design is pertaining to selective attention failures, focused attention failures and divided attention failures (Wickens, 1997). To maintain attention cockpit traffic displays (CDTI) will comprise a sizable collection of symbols, incorporate colors, use decluttering and various options for multiple applications (Shelden / Belcher, 1999). The CDTI should be error tolerant and guide or support the pilot in detecting errors before they become disastrous. The likelihood of operator errors can be reduced if the CDTI makes the execution of an action visible (Shelden, Belcher, 1999). The flight mode the aircraft is currently processing has to be incorporated into the CDTI. This ensures that the pilot is always aware of the mode. Access to the autopilot has to be possible at all times. The CDTI should provide visible information and can exploit items or moving parts to explain the purpose of the mode. This should reduce mode confusion. If the pilot interacts with the aircraft control panels, the autopilot should be automatically disconnected to give full authority to the pilot assuring avoiding the problem of fighting the autopilot in flight situations. Additionally, by utilizing both auditory and visual displays information of current flight status and options of aid in unexpected or emergency situations could support the pilot’s decision making to prevent serious accidents.

Colors have to be used carefully and with certain limitations. It is important that colors are incorporated with only a small number to ensure absolute judgement and correct identification and avoid distraction of the pilot. Color is appropriate to find a certain target or to project specific information on the display that is not related to another feature. An example of finding a target is the attempt to delineate the contours of an airport runway with different colors on a HUD display (Shelden / Belcher, 1999).

To facilitate the work of a pilot, in his responsibility over the passengers, the use of technology and an improvement of cockpit design are important to close the gap between the technological complexity and the cognitive capabilities of the pilot. Moreover, training of the pilot could support the pilot’s "knowledge of the world" but it must not be a substitute for inappropriate design.

Wickens, Sallie E. Gordon, Yili Liu (1997). An Introduction to Human Factors Engineering, Longman

Lovesey. Information flow between cockpit and aircrew, Ergonomics, 1995, vol. 38 No 3

Burgner, Norbert. High Tech Cockpits: Do they really help the pilot?,Flug Revue 5/97, Motor-Presse Stuttgart, Summarize and assessment of a survey of the German Pilot Association.report

Shelden, Belcher. Cockpit Traffic Displays of Tomorrow. Ergonomics in Design July 1999

Morrow, Daniel. Experience counts with Pilots, Ergonomics in Design April 1996

Norman, Donald. Design of Everyday Things,1990

Boers, R.M. Human Factors for General Aviation, University of Amsterdam, http://www.cs.vu.nl/~gerrit/GALLERY/RMBoers.htm

Mortimer, R.G. (1995) General Aviation Airplane Accidents Involving Spatial Disorientation. Proceedings of the Human Factors and Ergonomics Society Santa Monica, California: Human Factors Society

Accident report provided by the German "Institute for flight accident research " Bundesanstalt fuer Flugunfallforschung". No access for unauthorized persons!