DOT/FAA/AM-01/17 

Office of Aerospace Medicine 

Washington, DC 20591 

Human Factors 

Design Guidelines for 

Multifunction Displays 

Sig Mejdal


Michael E. McCauley


Monterey Technologies, Inc.


Monterey, CA 93940


Dennis B. Beringer


Civil Aerospace Medical Institute


Federal Aviation Administration


Oklahoma City, OK 73125


October 2001


Final Report


This document is available to the public


through the National Technical Information


Service, Springfield, VA 22161.


U.S. Department 

of Transportation 

Federal Aviation 

Administration 
N O TICE 

This document is disseminated under the sponsorship of 

the U.S. Department of Transportation in the interest of 

information exchange. The United States Government 

assumes no liability for the contents thereof. 
Technical Report Documentation Page 

1. eport No. 2. overnment Accession No. 3. ecipient's Catalog No. 

DOT/FAA/AM-01/17 

4. itle and Subtitle 5. Report Date 

Human Factors Design Guidelines for Multifunction Displays October 2001

6. erforming Organization Code 

7. uthor(s) 8. erforming Organization Report No. 

Mejdal, S.1, McCauley, M.E. 1, and Beringer, D.B. 

2 

9. erforming Organization Name and Address 10. Work Unit No. (TRAIS) 

1

Monterey Technologies, Inc. 2FAA Civil Aerospace Medical Institute 

Monterey, CA 93940 P.O. Box 25082 

Oklahoma City, OK 73125 11. Contract or Grant No. 

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered 

Office of Aerospace Medicine 

Federal Aviation Administration 

800 Independence Ave., S.W. 

Washington, DC 20591 14. Sponsoring Agency Code 

15. Supplemental Notes 

This report was supported by Contract # DTFA02-Q-90703, Approved Subtask # AM-A-00-HRR-519. 

16. Abstract 

References related to the design of multifunction displays are summarized into a series of human 

factors design guidelines. These are presented in a number of sections, which include: general 

guidelines, the design process, air traffic displays, weather displays, navigation displays, MFD 

menu organization, automation, individual displays, and general design principles for aircraft 

displays. Particularly relevant data graphs are included to illustrate some of the 

recommendations. These sections are followed by samples from the extant body of guidelines 

and standards. 

17. Key Words 18. Distribution Statement 

Document is available to the public through the 

National Technical Information Service; 

Multifunction Displays, Display Guidelines, Display 

Standards, Human Factors Design Guidelines, Navigation 

Displays, Automation Springfield, VA 22161 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 77 

R G R

T

P

A P

P

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 

i


ACKNOWLEDGMENTS 

This report was designed to provide background and guidelines for Federal Aviation Administration 

aviation safety inspectors approving multifunction displays for the cockpit. The information also may be 

useful for the designers of those displays. 

This document was produced by Monterey Technologies, Inc. under DTFA02-Q-90703, Purchase 

Order No. 8-10446 to the Federal Aviation Administration, Civil Aerospace Medical Institute (CAMI). Dr. 

Michael McCauley served as program manager for Monterey Technologies, Inc. Dr. Dennis Beringer served 

as the technical monitor for CAMI. The authors appreciate the input of Colleen Donovan, AIR-130, FAA 

Headquarters. 

iii 

TABLE OF CONTENTS


1.0 INTRODUCTION ...............................................................................................................................1


1.1 History of Displays.................................................................................................................................1


1.2 Glass Cockpit..........................................................................................................................................1


1.3 Applications ............................................................................................................................................1


1.4 Multifunction Displays ..........................................................................................................................2


1.5 Project Objectives ...................................................................................................................................2


1.6 Purpose of Guidelines ............................................................................................................................2


1.7 Report Organization ..............................................................................................................................4


2.0 METHODS ...........................................................................................................................................4


2.1 Constraints and Assumptions ................................................................................................................4


2.2 Literature Reviewed ................................................................................................................................4


3.0 FINDINGS.............................................................................................................................................5


3.1� General Guidelines .................................................................................................................................5


Smith and Mosier (1986) ......................................................................................................................5


Molich and Nielsen (1990) ...................................................................................................................5


Woodson, Tillman, and Tillman (1992) ..............................................................................................5


Shneiderman (1992) ..............................................................................................................................6


Helander, Landauer, and Prabhu (1997) ..............................................................................................6


Lund (1995) ...........................................................................................................................................8


U.S. Nuclear Regulatory Commission (1994) ......................................................................................9


FAA (1996).............................................................................................................................................9


Microsoft Corporation (1998) ...............................................................................................................9


IBM Corporation (1998) .................................................................................................................... 11


3.2 Design Process ..................................................................................................................................... 11


3.3 Generalizing From Applied Research ................................................................................................. 13


4.0 HUMAN FACTORS GUIDELINES DERIVED FROM RESEARCH .......................................... 14


4.1� Air Traffic Displays ............................................................................................................................. 14


Depth Cues as Traffic Display Aids.................................................................................................... 14


Color-Coded Traffic Information ........................................................................................................ 15


4.2� Weather Displays ................................................................................................................................ 16


Rotating versus Fixed Weather Displays ............................................................................................ 16


4.3� Navigation Displays ............................................................................................................................ 17


Navigation Display Integration .......................................................................................................... 17


Rotating versus Fixed Navigation Displays ........................................................................................ 18


3D Display Elevation Angle ............................................................................................................... 19


Taxiway navigation maps: HUD and 3D vs. 2D ............................................................................... 19


4.4� MFD Menu Organization .................................................................................................................. 21


Introduction to Multifunction Display Menus ................................................................................. 21


MFD Menu Organization .................................................................................................................. 21


Depth versus Breadth in MFD Menus ............................................................................................... 22


Varied Breadth in MFD Menus ......................................................................................................... 23


Item Selection in MFD Menus ........................................................................................................... 24


Item Organization in MFD Menus .................................................................................................... 25


Speech-Based Control of MFD Menus ............................................................................................... 26


Shortening Navigational Distance in an MFD Menu........................................................................ 26


Category Organization in an MFD Menu ......................................................................................... 27


v

Organizational Aids for the Design of an MFD Menu ...................................................................... 29


Network Structures in an MFD Menu ............................................................................................... 29


Adding Descriptors to the MFD Menu ............................................................................................. 30


Debunking the Icon Myth.................................................................................................................. 31


4.5 Automation .......................................................................................................................................... 32


Cockpit Automation............................................................................................................................ 31


Automation Problems: Feedback ........................................................................................................ 33


Automation Problems: Complexity .................................................................................................... 34


Automation Problems: Workload ....................................................................................................... 34


Automation: Human-Centered Approach .......................................................................................... 35


4.6 Individual Displays ............................................................................................................................. 36


3D versus 2D Displays ....................................................................................................................... 36


Component Arrangement ................................................................................................................... 39


Screen Layout ...................................................................................................................................... 40


Pictorial Displays................................................................................................................................. 41


Design of Icons and Symbols .............................................................................................................. 42


Icons: Complexity and Concreteness .................................................................................................. 43


4.7 General Design Principles for Aircraft Displays ................................................................................. 44


The Principle of Pursuit Tracking ...................................................................................................... 44


The Principle of the Moving Part ....................................................................................................... 45


Proximity Compatibility Principle...................................................................................................... 45


Emergent Features ............................................................................................................................... 46


Command and Status Displays ........................................................................................................... 48


Displaying Uncertainty ....................................................................................................................... 48


5.0� SAMPLES FROM EXISTING GUIDELINES OR STANDARDS ................................................. 49


Boff and Lincoln (1988) Engineering Data Compendium................................................................ 49


Clay (1993) DOT-FAA-93-18 ........................................................................................................... 50


Department of Defense (1991) MIL-STD-411E .............................................................................. 51


Department of Defense (1984) MIL-STD-783D ............................................................................. 51


Department of Defense (1984) MIL-STD-1295A ............................................................................ 52


Department of Defense (1989) MIL-STD-1472D ........................................................................... 52


Department of Defense (1996) MIL-STD-1472E ............................................................................ 53


Department of Defense (1996) MIL-STD-1787B ............................................................................ 53


Department of Defense (1989) MIL-HDBK-761A .......................................................................... 54


Federal Aviation Administration (1994) AC 20-130A ...................................................................... 55


Federal Aviation Administration (1987) AC 25-11 ........................................................................... 55


Federal Aviation Administration (1996) ............................................................................................ 56


Federal Aviation Administration (1992) TSO-C129 ......................................................................... 57


NASA (1987) NASA-STD 3000 ........................................................................................................ 57


Nuclear Regulatory Commission (1996) NUREG-0700.................................................................. 58


NATO Standardization Agreement (1992) STANAG 3705 ............................................................. 58


RTCA (1991) RTCA Document No. RTCA/DO-208 .................................................................... 59


RTCA (1996) RTCA Document No. RTCA/DO-229 .................................................................... 59


Society of Automotive Engineers (1969, reaffirmed 1991) AIR-1093 ............................................. 60


Society of Automotive Engineers (1988) ARP-4032 ......................................................................... 60


Society of Automotive Engineers (1995) ARP-4033 ......................................................................... 61


Society of Automotive Engineers (1988) ARP-4102 ......................................................................... 61


Society of Automotive Engineers (1997) ARP 5108 ......................................................................... 62


6.0 REFERENCES .................................................................................................................................... 62


vi

HUMAN FACTORS DESIGN GUIDELINES FOR MULTIFUNCTION DISPLAYS


1. INTRODUCTION 

1.1 History of Displays 

The current advanced displays seen in a state-ofthe-art transport aircraft reflect over a century of 

development. From the Wright Brothers’ piece of 

string used as a slip indicator to the modern elec�

tronic glass cockpits, the cockpit display has been the 

means of presenting information directly to the pilot. 

“It is these aircraft displays that are the pilot’s win�

dow on the world of forces, commands, and informa�

tion that cannot be seen as naturally occurring visual 

events or objects” (Stokes & Wickens, 1988). 

Serious attention was not given to display develop�

ment until the advent of the need to fly without visual 

references and the subsequent “development of a 

usable gyroscope that could be applied in the form of 

an artificial horizon” (Hawkins, 1987). From this 

serious attention, came serious advancements. Later, 

another technological breakthrough that advanced 

the state of displays was the rapid development of 

electronics. This enabled “servo-driven instruments 

to become possible in the 1950s and then gave the 

designer the freedom to locate the sensor away from 

the actual instrument” (Hawkins, 1987). 

As digital avionics technology has continued to ad�

vance, and as air transport has become a popular means 

of travel, there has been an increased focus on aviation 

safety, human factors and display design. As aircraft 

performance was increasing, more information was 

made available to the pilot, and both the number and 

complexity of displays were increasing. “As aircraft grow 

in complexity and as technology provides the capability 

of offering more and more information, the pilot’s 

senses can become overloaded with information” (Statler, 

1984). The limits of human information processing 

may be exceeded by the overwhelming increase of 

warning indicators, status displays, flight path displays, 

air traffic control data links, meteorological informa�

tion, navigational information, and communications 

data. Accordingly, the necessity for well-designed dis�

plays is more important now than it ever has been. Also, 

because of the “tremendous capabilities of the on-board 

computers to analyze, sort, integrate, and route infor�

mation from a wide variety of sensors and subsystems, 

the designers now have fewer constraints and more 

freedom concerning the location and design of the 

displays” (Sexton, 1988), as well as opportunities for 

automation. 

1.2 Glass Cockpit 

The period from 1970 to the present has been 

marked by major changes in the appearance of the 

flight deck due to the introduction of electronic 

display units (EDU) (Billings 1997). The term “glass 

cockpit” is synonymous with multi-function displays 

(MFDs). A typical glass cockpit configuration in�

cludes up to 6 electronic display units, backup flight 

instruments (liquid crystal displays or electrome�

chanical instruments) and a few critical systems indi�

cators on the main instrument panel (Billings, 1997). 

“Aircraft systems controls are located on the overhead systems panel. A mode control panel, also called 

a flight control unit, is located centrally on the glare 

shield below the windscreens. Other flight manage�

ment system control units and communications con�

trols are located on the pedestal between the pilots, 

together with power and configuration controls” 

(Billings, 1997). 

1.3 Applications 

In the early 1980s, the all-digital AirBus A310 and 

Boeing 757/767 “introduced cathode ray tube (CRT) 

flight displays in civil aviation and this marked the 

watershed in the evolution of the glass cockpit. While 

the technology employed in the displays was not 

significantly different, conceptually the A310” 

(Hawkins, 1987) displays were more advanced than 

those of the Boeing aircraft. According to Hawkins 

(1987), “Boeing used an Electronic Attitude Direc�

tor Indicator (EADI), the display details of which 

were similar to those of the electromechanical ADI 

that it replaced.” On the other hand, Airbus was able 

to take advantage of the flexibility of the new displays 

and elected to introduce a Primary Flight Display 

(PFD) that integrated the “main airspeed indication, 

selected altitude and deviation, full flight mode annun�

ciation and various other information” (Hawkins, 1987). 

1

In addition to flight instrument displays, glass 

cockpit technology also can be applied to the presen�

tation of systems information. This involves engine 

data as well as other aircraft systems. “The flexibility 

of this time-sharing form of display enables systems 

information to be presented only when required, 

either because of the phase of operation, such as 

engine starting, or when a system deviates from its 

normal operating range.” (Hawkins, 1987). 

Another use of MFD technology is for the flight 

management system (FMS). The FMS interfaces with 

the navigation system and is intended to reduce 

workload, compile complicated lateral and vertical 

profiles, and supply data for the electronic flight 

guidance system. In general these systems optimize 

operating efficiency with a primary aim of reducing 

fuel costs (Hawkins 1987). 

The flexibility of glass cockpit displays has made it 

possible to provide information when it is needed, in 

new and different formats, and to modify that informa�

tion in any way desired by designers to fit any need. 

1.4 Multifunction Displays 

The multifunction display (MFD) is a display 

surface which, through hardware or software controlling means, is capable of displaying information from 

multiple sources and, potentially, in several different 

reference frames. The device may be capable of either 

displaying different groups of data (i.e., weather, 

traffic, or terrain) one at a time or in a combined 

fashion. In some cases the data may be combined 

within a single common reference frame or within 

separate reference frames. 

The advances in technology combined with decreases in cost have led to design flexibility of the 

cockpit displays. As a result, MFDs are becoming 

increasingly prevalent in aviation. MFDs have been 

promoted as a means of “layering” information in 

integrated formats and of using single display sur�

faces to present large amounts of data. MFDs are 

capable of presenting data from a number of indepen�

dent sources, including those from Cockpit Display 

of Traffic Information (CDTI) systems, enhanced 

navigational information systems supporting mov�

ing maps, weather information sources, Traffic Alert 

Collision Avoidance Systems (TCAS), and Terrain 

Avoidance Warning Systems (TAWS). Human fac�

tors issues arise when avionics subsystems evolve 

independently, without consistency in the design of 

the user interfaces, and are brought together in the 

cockpit. Cockpit MFDs create the opportunity for a 

variety of systems to be displayed either simulta�

neously on adjacent display surfaces, sequentially, in 

layers on the same display surface, or simultaneously 

in “windows” on the same display surface. If MFD 

users are confronted with conflicting, mismatched, 

and inconsistent display designs, either at the level of 

display construction and formatting or at the level of 

data accession method, effective use of the displayed 

data is likely to be compromised. 

1.5 Project Objectives 

There are numerous guidelines and standards re�

lating to the basic design of a number of uni-func�

tional displays. However, guidelines are needed for 

the design, operation, and evaluation of MFDs in the 

cockpit to promote safety and enhance flight crew 

performance. 

The need for guidance in the design and use of 

MFDs has been recognized at several levels within the 

aviation community. Guidelines and standards can 

have value to numerous participants in this commu�

nity, including the manufacturers, the regulators, 

and the consumers. Manufacturers have recently requested guidance from the Aircraft Certification Ser�

vice of the FAA regarding the design of MFDs, with 

the intent to provide systems meeting the require�

ments of certification for use in aircraft. In a parallel 

development, similar guidance is being sought in the 

development of guidelines, standards, and certifica�

tion procedures for the aircraft concepts being devel�

oped and tested in the NASA-coordinated Advance 

General Aviation Transport Experiments. Data also 

are needed in the development of the MFD concept 

for the Flight 2000 program and the freeflight envi�

ronment. In addition, work is proceeding within 

SAE (the G-10 Subcommittee, Human Factors) to 

draft an Aerospace Recommended Practice docu�

ment on the design and use of MFDs. Thus, it is the 

hope that this report will be useful to both the shortand long-term efforts described above. 

1.6 Purpose of Guidelines 

The Department of Defense document, Military 

Standard: Human Engineering Design Criteria Stan�

dard for Military Systems, Equipment and Facilities, 

MIL-STD-1472D (1989), states: 

Visual displays should be used to provide the operator 

with a clear indication of equipment or system 

conditions for operation under any eventuality 

2

commensurate with the operational and maintenance 

philosophy of the system under design. 

This statement, while true, is not particularly 

helpful or useful to a designer or evaluator because 

the statement is, by need of being overarching, rather 

vague. Part of the solution to this problem is the use 

of more detailed and specific design guidelines. 

“A large number of interface design guidelines 

have been developed and can be of great value to the 

designer. Although guidelines cannot guarantee the 

success of a design, they may prevent the designers 

from developing interfaces that will clearly be unde�

sirable” (Liu, 1997). It is important to remember that 

a display guideline is simply a tool that might be used 

in a particular stage of the design process. 

According to Sanders and McCormick (1993), 

Human Factors is not just applying checklists and 

guidelines. To be sure, human factors people develop 

and use checklists and guidelines; however, such aids 

are only part of the work of human factors. There is 

not a checklist or guideline in existence today that, if it 

were applied blindly, would ensure a good human 

factors product. Trade-offs, considerations of the specific 

application, and educated opinions are things that 

cannot be captured by a checklist or guideline but are 

all important in designing for human use. 

“If guidelines are proposed for application in a 

variety of systems, then they must be written in 

general terms.” (Smith & Mosier, 1984). For example, “a guideline that said ‘every display should 

have a capitalized title centered in the second line’ 

would be too restrictive. Such a guideline would 

constitute a specific design rule that might be satis�

factory in some applications but not in others.” 

(Smith & Mosier, 1984). A more general representa�

tion of this design concept could be stated, “every 

display should be consistently identified in some 

distinctive way.” This guideline would now have a 

much broader application. Of course, display design�

ers may be disappointed to encounter this guideline 

if they were expecting a specific rule, only to find 

general advice instead (Smith & Mosier 1984). Herein 

lies the paradox: The display designer wants specific 

rules to apply to a specific design problem. However, 

specific rules can only be created when one has a full 

understanding of both the design objectives and 

constraints within which the design is being created, 

and these vary widely from application to applica�

tion. Thus, one is faced with creating either general 

guidelines which are somewhat applicable to many 

designs (and require modification for specific appli�

cation) but are specifically applicable to few as written, or specific guidelines that apply to the design 

problem at hand, but may not generalize to other 

design problems. 

Guidelines can be thought of as “answers” to display 

questions. Each display has a unique set of issues and 

“questions,” therefore, no collection of guidelines can 

exist that will be able to answer each of the unique 

questions that arise as the designer progresses through 

the display design process. It is naïve to think that a set 

of guidelines will result in a well-designed interface. 

Display design is a creative process and there are no 

formulas that can insure a successful design (Andre, 

personal communication, 1998). 

To realize “the great value” of guidelines described 

by Liu (1997), the general guidelines must be trans�

lated or converted into specific rules that the designer 

can follow. So often, designers dismiss the guidelines 

because they are “too general and of no use.” These 

types of guidelines are purposely general to allow the 

designer to develop his/her own design rules from 

these “vague” recommendations. 

“Application of guidelines will thus involve ques�

tions of how they should be converted into design 

rules, who should do it, and when” (Smith & Mosier, 

1984). At the same time, the appropriateness of 

generalizing from the many “specific” results ob�

tained in particular environments (typically based on 

research findings) to the current design environment 

also must be analyzed. 

Design rules should be established “early in the 

design process, before any actual design of user interface software” (Smith & Mosier, 1984). The design 

rules should be the joint responsibility of systems 

analysts assessing design requirements, software designers assessing feasibility, their managers, and po�

tential end-users (Smith & Mosier, 1984). 

“Establishment of design rules might begin with 

review of the guidelines material. Certain guidelines 

might be discarded as being irrelevant to the particu�

lar situation. Other guidelines might be modified” 

(Smith & Mosier, 1984), and other guidelines may 

be generalized to the present design situation. All 

guidelines that are accepted for use should be reworded as necessary to convert them into accepted 

design rules. In that conversion, some guidelines 

might be considerably expanded. For example, “a 

guideline that says displays should be consistently 

3

formatted might be converted into a series of eight or 

ten rules specifying the exact format to be adopted for 

different elements in a display” (Smith & Mosier, 

1984). This process enables specific design rules to be 

derived from the guidelines material. The develop�

ment of specific design rules should be performed as 

an integral part of the design process, serving to focus 

attention on critical design issues and to establish 

specific design requirements (Smith & Mosier, 1984). 

1.7 Report Organization 

This report is organized to be compatible with the 

information in the previous sections. The first sec�

tion of the Findings is titled General Guidelines. In 

this section, the more general design objectives, guidelines, and recommendations are described. From 

these general guidelines, deletion, acceptance, modi�

fication, and expansion will take place to create more 

specific guidelines (e.g., design rules). 

The second section describes the design process 

recommended for the designers of any display to 

arrive at their own guidelines or “answers” for their 

specific display. Pre-existing guidelines are used dur�

ing various steps of this recommended process. 

The third section discusses many of the display 

design issues and the research and results associated with 

them. 

The fourth section provides samples of existing stan�

dards and guidelines for human factors issues in display 

design from DoD, FAA, NRC, SAE and other sources. 

2. METHODS 

2.1 Constraints and Assumptions 

The selection of literature and the development of 

the guidelines were constrained for several reasons. 

First, the primary focus of this effort was concerned with 

issues unique to multi-function displays, so the majority 

of the research reports collected dealt with multi-func�

tion issues, as opposed to uni-function displays. The 

scope of this project was not intended to be a restate�

ment of the basic tenets of display design, as represented 

in many existing handbooks and references on uni�

functional displays. However, when these sources con�

tributed useful data or when they addressed the basic 

display-design/format issues where problems unique to 

MFDs are encountered, they were included. Some of 

the general display design guidelines for uni-functional 

displays are pertinent to the multi-function display 

issues, and accordingly, are included and discussed 

within the document. 

2.2 Literature Reviewed 

Literature related to the design of, or issues associ�

ated with, multi-function displays was collected from 

a variety of sources for review. First were the existing 

display guideline documents. These were not neces�

sarily from the aviation community but included any 

appropriate sources from the display design popula�

tion. Examples include: 

•� Design Guidelines for User-System Interface Software (Smith & Mosier, 1984) 

•� Handbook of Human-Computer Interaction 

(Helander, Landauer, & Prabhu, 1997) 

• Designing the User Interface (Shneiderman, 1992) 

•� Human-Computer Interface Guidelines (Goddard 

Space Flight Center, 1992) 

•� Advanced Human-System Interface Design Review 

Guideline (U.S. Nuclear Regulatory Commission, 

1985) 

Standards, recommended practices, and standard 

practice documents also were reviewed. References 

from these types of sources included: 

• Pilot-System Integration (Aerospace Recommended 

Practice, 1988) 

• Transport Category Airplane Electronic Display Sys�

tems (FAA Advisory Circular, 1987) 

• Human Engineering Design Criteria for Controls 

and Displays in Aircrew Stations (NATO Standard�

ization Agreement, 1992) 

• Operations Concepts for Cockpit Display of Traffic 

Information Applications (RTCA Special Committee Report, 1998) 

Human factors and ergonomic handbooks also 

were examined. These titles included: 

• Handbook of Human Factors and Ergonomics 

(Salvendy, 1997) 

• Human Factors Design Handbook (Woodson, 

Tillman, & Tillman, 1992) 

• Engineering Data Compendium: Human Percep�

tion and Performance (Boff & Lincoln, 1988a-i). 

Several scientific journals were examined, including: 

• Human Factors 

• International Journal of Aviation Psychology 

• Ergonomics. 

4

Proceedings included those from the 

• Human Factors and Ergonomics Society 

• International Conference on Human-Computer In�

teraction in Aeronautics 

• Digital Avionics System Conference 

• SAE/AIAA World Aviation Congress 

• Silicon Valley Ergonomics Conference. 

Other sources for information included books on 

aviation human factors and on general design. These 

sources included: 

• Human Factors in Aviation (Wiener & Nagel, 1988) 

• Human Factors in Flight (Hawkins, 1987) 

• Aviation Automation (Billings, 1997) 

• Design for Success: A Human-Centered Approach to 

Designing Successful Products and Systems (Rouse, 

1991) 

• To Engineer is Human: The Role of Failure in 

Successful Design (Petroski, 1985) 

• The Design of Everyday Things (Norman, 1990) 

Several seminal references were too lengthy to 

excerpt in meaningful fashion, containing explicit 

and detailed data on airborne display applications. 

These sources are recommended for those readers 

requiring highly specific detail, and include: 

• Analysis of human factors data for electronic flight 

display systems (Semple, Heapy, Conway & Burnett, 

1971) 

• Design criteria for airborne map displays (Carel, 

McGrath, Hershberger, and Herman, 1974) 

• Design and use of computer-generated electronic 

area navigation map displays (Streeter, Weber, and 

McGrath, 1973) 

In addition to these published works, conversa�

tions with aviation researchers, commercial pilots, 

cockpit designers, and consumer product designers 

were conducted to better understand some of the 

display design issues and tradeoffs, and equipment 

functionality and shortcomings of present systems. 

3. FINDINGS 

3.1 General Guidelines 

This section describes the general display guidelines that we encountered. Many of these principles 

are global in scope and subject to interpretation. 

These types of guidelines can be converted into more 

specific guidelines during the design process (see 

section above on Guidelines under Project Objec�

tives). The sources of these General Guidelines in�

clude human factors handbooks, user-interface 

handbooks, government requirement documents, and 

software manufacturers’ guidelines. A larger sample of 

existing guidelines published by government or stan�

dards-defining organizations is given in Section 4. 

Smith and Mosier (1986) 

The following principles are described by Smith 

and Mosier (1986) in their section on Data Display: 

Display only and all the necessary data to the 

user. At any step in the sequence, ensure that whatever data a user needs will be available for display. 

Tailor the display of the data to user needs, providing 

only necessary and immediately usable data at any 

step in the process. The designer of user interface 

software must employ some method of task analysis 

to determine a user’s detailed information require�

ments. 

1) Display the data in a usable form. Do not require a 

user to transpose, compute, interpolate, or translate 

displayed data into other units, or refer to docu�

mentation to determine the meaning of displayed 

data. 

2) Display the data consistent with user convention. 

If no specific user conventions have been established, 

adopt some consistent data display standards. 

3) Maintain a consistent display format from one 

display to another. 

4) Use consistent, familiar wording with a minimal 

use of abbreviations. 

Molich and Nielsen (1990) 

Molich and Nielsen (1990) presented the follow�

ing design heuristics concerning user interfaces: 

1) Use simple and natural dialogue. 

2) Speak the user’s language. 

3) Minimize the memory load. 

4) Be consistent. 

5) Provide feedback. 

6) Provide clearly marked exits. 

7) Prevent errors. 

8) Provide good error messages. 

Woodson, Tillman, and Tillman (1992) 

Woodson, Tillman, and Tillman (1992) present 

the following “General Guidelines for the Selection 

and Design of Visual Displays” in their Human 

Factors Design Handbook: 

5

1) Use the simplest display concept commensurate 

with the information transfer needs of the operator 

or observer. The more complex the display, the 

more time it takes to read and interpret the informa�

tion provided by the display, and the more apt the 

observer or operator is to misinterpret the informa�

tion or fail to use it correctly. Avoidance of com�

plexity is another way of stating the KISS (Keep It 

Simple, Stupid) principle that is a cornerstone of 

applied ergonomics (Salvendy, 1997). 

2) Use the least precise display format that is com�

mensurate with the readout accuracy actually re�

quired and/or the true accuracy that can be generated 

by the display-generating equipment. Requiring op�

erators to be more precise than necessary only increases their response time, adds to their fatigue or 

mental stress, and ultimately causes them to make 

unnecessary errors. 

3) Use the most natural or expected display format 

commensurate with the type of information or in�

terpretive response requirements. Unfamiliar formats require additional time to become accustomed 

to them, and they encourage errors in reading and 

interpretation as a result of unfamiliarity and inter�

ference with habit patterns. When new and unusual 

formats seem to be needed, consider experimental 

tests to determine whether such formats are com�

patible with basic operator capabilities and limita�

tions and/or whether the new format does in fact 

result in the required performance level. 

4) Use the most effective display technique for the 

expected viewing environment and operator viewing conditions. 

Optimize the following display features: 

• Visibility 

• Conspicuousness: Ability to attract attention and 

distinguishability from background interference 

and distraction 

• Legibility 

• Interpretability: Meaningfulness to the intended 

observer within the environment 

Shneiderman (1992) 

In Designing the User Interface, Shneiderman bases 

his display guidelines on an earlier work by Smith and 

Mosier (1984). 

1) Consistency of data displays. This principle is fre�

quently violated, but it is easy to repair. During the 

design process, the terminology, formats and so on 

should all be standardized and controlled. 

2) Efficient information assimilation by the user. The 

format should be familiar to the operator and re�

lated to the tasks required to be performed with the 

data. 

3) Minimal memory load on user. Do not require the 

user to remember information from one screen for 

use on another screen. Arrange tasks such that 

completion occurs with few commands, minimiz�

ing the chance of forgetting to perform a step. 

4) Compatibility of data display with data entry. 

5) Flexibility for user control of data display. Users 

can get the information in the form most conve�

nient for the task they are working on. 

Lockheed Missiles and Space Company (1981) 

Lockheed (1981) details general display design 

objectives as such: 

1) Be consistent in labeling and graphic conventions. 

2) Standardize abbreviations. 

3) Use consistent format in all displays. 

4) Present data only if they assist the operator. 

5)� Present information graphically, where appropriate, 

using techniques that relieve the need to read and 

interpret alphanumeric data. 

6)� Present digital values only when knowledge of nu�

merical value is actually necessary and useful. 

7) Design a display in monochromatic form, using 

spacing and arrangement for organization, and then 

judiciously add color where it will aid the operator. 

8) Involve operators in the development of new dis�

plays and procedures 

Helander, Landauer, and Prabhu (1997) 

The Handbook of Human-Computer Interaction 

(Helander, Landauer, & Prabhu, 1997) includes a 

section that provides guidance in the use of Graphical 

User Interfaces. The authors state that these recom�

mendations can be generically applied to all GUIs: 

1)� A GUI design must account for the following char�

acteristics: 

• Metaphor: comprehensible images, concepts, or 

terms. 

• Mental Model: appropriate organization of data, 

functions, tasks, and roles. 

6

• Navigation: efficient movement among the data, 

functions, tasks, and roles via windows, menus, 

and dialogue boxes. 

• Appearance: quality presentation characteristics, 

or look. 

• Interaction: effective input and feedback se�

quencing. 

2) Three key principles guide GUI design: 

• Organization: Provide the designer with a clear 

and consistent conceptual structure. 

• Economy: Maximize the effectiveness of a mini�

mal set of cues. 

• Communication: Match the presentation to the 

capabilities of the user. 

3) Order and Chaos: Organization lends order to a 

GUI, making it easier for the user to understand and 

navigate. Without visual and cognitive organiza�

tion, the GUI becomes chaotic and, therefore, diffi�

cult to learn and use. 

4) Consistency: The principle of internal consistency 

says to observe the same conventions and rules for 

all elements of the GUI. Without a strong motivat�

ing reason, casual differences cause the viewer to 

work harder to understand the essential message of 

the display. The GUI should deviate from existing 

conventions only when doing so provides a clear 

benefit to the operator. In other words, the GUI 

should have a good reason for being inconsistent. 

5) External Consistency: Leverage Known Design 

Techniques – The GUI should be designed to 

match the user’s expectations and task experience, 

rather than force users to understand new prin�

ciples, tasks, and techniques. 

6)� GUI Screen Layout: There are three primary means 

of achieving an organized screen layout: 

• Use an underlying layout grid. 

• Standardize the screen layout. 

• Group related elements. 

7) Visual Relationships: Another technique helpful in 

achieving visual organization is to establish clear 

relationships by linking related elements and disas�

sociating unrelated elements through their size, 

shape, color, texture, etc. 

8) Navigability: An organized GUI provides an initial 

focus for the viewer’s attention, directs attention to 

important, secondary, or peripheral items, and as�

sists in navigation. 

9) Economy: Economy concerns achieving effects 

through modest means. Simplicity suggests that 

including only those elements that are essential for 

communication. For information intensive situa�

tions, the design should be as unobtrusive as pos�

sible. Some guidelines regarding economy include 

the following: 

• Modesty: In general, GUI components should be 

modest and inconspicuous. Users should be al�

most unaware of the GUI working to convey 

meaning. 

• Clarity: Components should be designed with 

unambiguous meanings. 

• Distinctiveness: Distinguish the important prop�

erties of essential elements. 

• Emphasis: In general, make the most important 

elements salient. De-emphasize non-critical ele�

ments, and minimize clutter so that critical infor�

mation is not hidden. 

10)Balanced Communication: To communicate suc�

cessfully, a GUI designer must balance many fac�

tors. Well-designed GUIs achieve this balance 

through the use of information-oriented, systematic 

graphic design. This refers to the layout, typogra�

phy, symbols, color, and other static and dynamic 

graphics to convey facts, concepts, and emotions. 

11)Symbolism: GUI symbolism refers to signs, icons, 

and symbols that can help to communicate complex 

information and make the display more appealing. 

In general keep in mind the following: 

• Use symbols or icons that are clear and unam�

biguous 

• Use familiar references when possible. 

• Be consistent in size, angles, weights, and visual 

density of all the signs. 

12)Multiple Views: One important technique for im�

proving communication within a GUI is to provide 

multiple views of the display of complex structures 

and processes. 

13)Advantages of Color: Color, including texture, is a 

powerful communication tool; so powerful, in fact, 

that color is easy to misuse or overuse. GUI design�

ers must, therefore, understand color’s functions so 

as to use it with proper skill and sophistication. 

Some of the most important tasks color can accom�

plish are these: 

• Emphasize important information 

• Identify subsystems or structures 

• Portray natural objects realistically 

7

• Portray time and progress 

• Reduce errors of interpretation 

• Add coding dimensions 

• Increase clarity or comprehensibility 

• Increase believability and appeal 

14) In general, similar colors imply a relationship among 

objects. Therefore, color should be used to group 

related items, and a consistent color code should be 

used for screen displays. 

15) Color Economy 

• Redundancy - The principle of color economy 

suggests using a maximum of 5 ± 2 colors where 

meaning must be remembered. Notice that this 

maximum is even less than the 7 ±2 which refers 

to the human cognitive functioning limit with 

short term memory. If appropriate, use redun�

dant coding based on shape as well as color. 

• Sequencing – To code a large set of colors, use the 

spectral sequence; red, orange, yellow, green, blue, 

and violet. Use redundant coding of shape as well 

as color. This technique aids those with color 

deficient vision and makes the display more resil�

ient to color distortions caused by ambient light 

changes. 

16) Color Emphasis: Color emphasis suggests using 

strong contrast in value and chroma to focus the 

operator’s attention on critical information. The 

use of bright colors for danger signals, attentiongetters, reminders, and pointers is entirely appropri�

ate. High-chroma red alerts seem to aid faster 

response than yellow or yellow-orange if brightness 

is equal. When too many figures or background 

fields compete for the viewer’s attention, confusion 

arises, as can happen in the approach to color design 

that makes displays look appropriate for Las Vegas. 

Also, older viewers may be less able to distinguish 

blue from white and blue-green for bluish-white 

light due to natural aging and change of coloration 

of the lens of the eye. 

17) Color Symbolism: Remember the importance of 

symbolism in communication: Use color codes that 

respect existing cultural and professional usage. 

Lund (1995) 

In a 1995 study, Lund conducted a revealing 

survey of experienced professionals requesting that 

they order a collection of general “rules of thumb” 

based on their relative impact on usability. The 

following is an ordered listing of the rules that were 

believed to have the largest impact on usability. 

• Know the user, and you are not the user. 

• Things that look the same should act the same. 

• Everybody makes mistakes, so every mistake 

should be fixable. 

• The information for the decision needs to be 

there when the decision is needed. 

• Error messages should actually mean something 

to the user, and tell the user how to fix the 

problem. 

• Every action should have a reaction. 

• Don’t overload the user’s buffer. 

• Consistency, consistency, consistency. 

• Minimize the need for a mighty memory. 

• Keep it simple. 

• The more you do something, the easier it should 

be to do. 

• The user should always know what is happening. 

• The user should control the system. The system 

shouldn’t control the user. The user is the boss, 

and the system should show it. 

• The idea is to empower the user, not speed up the 

system. 

• Eliminate unnecessary decisions, and illuminate 

the rest. 

• If the user made an error, let the user know about 

it before getting into real trouble. 

• The best journey is the one with the fewest steps. 

Shorten the distance between users and their goals. 

• The user should be able to do what the user wants 

to do. 

• Things that look different should act different. 

• The user should always know how to find out 

what to do next. 

• Do not let users accidentally cause themselves 

difficulty. 

• Even experts are novices at some point. Provide 

help. 

• Design for regular people and the real world. 

• Keep it neat. Keep it organized. 

• Provide a way to bail out and start over. 

• The fault is not in the user, but in the system. 

• If it is not needed, it’s not needed. 

• Color is information. 

• Everything in its place, and a place for everything. 

8

U.S. Nuclear Regulatory Commission (1994) 

The U.S. Nuclear Regulatory Commission pro�

duced the 1994 document entitled Advanced Human-System Interface Design Review Guidelines. Within 

this document the following general display guidelines were given: 

1) Displays should present the simplest information 

consistent with their function, information irrel�

evant to the task should not be displayed, and 

extraneous text and graphics should not be present. 

2)� All information required by the crewmember dur�

ing a transaction should be available on the current 

display. 

3) When displays are partitioned into multiple pages, 

function/task related information items should be 

displayed together on one page. 

4)� Information depicted on a display should be grouped 

according to obvious principles (e.g., task, system, 

function, sequence) based on crewmember require�

ments in performance of the ongoing task. 

5) Visual or auditory feedback should be provided to 

indicate that a display input has been registered and 

that the system response or action is obvious. 

FAA (1996) 

The Federal Aviation Administration also pro�

duced a guide to assist in the design of new systems 

and equipment, Human Factors Design Guide for 

Acquisition of Commercial Off-the-Shelf Subsystems, 

Non-Developmental Items, and Developmental Systems 

(FAA-CT-96-1, 1996). General principles of basic 

screen design were given as follows: 

1) Simplicity – Information should be presented sim�

ply and in a well-organized manner. Ways to achieve 

simplicity include the following: 

• The screen should appear to be orderly and clut�

ter-free. 

• Information should be presented in consistent, 

predictable locations. 

• The language used should be plain and simple. 

• Interrelationships should be indicated clearly. 

2) Logical grouping – Data items on a screen should be 

grouped on the basis of some logical principle. 

3) Minimal movement – Screens should be designed 

to minimize eye movement. 

4) What information to display – The information to 

be displayed should be prioritized so that the most 

important or critical information can be displayed 

all the time, and less important or critical informa�

tion can be displayed upon s user’s request. 

5) Minimal information density – The amount of 

information per unit area should be minimized by 

presenting only information that is essential to a 

user at any given time. 

6) Screen density – For text displays, the ratio of 

characters to blank spaces should not exceed 60 

percent. 

7) Integrated information – If a user needs a variety of 

data to complete a task, those data should be 

provided in an integrated display, not partitioned 

in separate windows or screens. 

8)� Directly usable form – Information shall be pre�

sented to a user in directly usable form; a user shall 

not have to decode or interpret. 

9) Consistent screen structure – Screens throughout a 

system shall have a consistent structure that is 

evident to users. 

10) Instructions and error messages – Instructions and 

error messages shall appear in a consistent location 

on the screen. 

11) Maintaining context – An application should provide a means for ensuring that a user maintains an 

understanding of the context in which a task is 

being performed. For example, the application 

might display the results of those previous transac�

tions that affect the current one, or it might display 

currently available options. 

12) Operational mode – If an application provides 

different operational modes, the current mode shall 

be continuously indicated to a user. 

13) Current context indication – If the consequence of 

a control entry will differ depending upon the 

context established by a prior action, a continuous 

indication of current context should be displayed. 

14) Action history – If appropriate, an application shall 

maintain a summary of the transactions that pro�

duced the current context and display it at a user’s 

request. If desirable, an UNDO feature should be 

linked to each step of the action history. 

Microsoft Corporation (1998) 

Software manufacturers use principles and guidelines during the design of their products. Following 

is a sample of Microsoft and IBM’s design principles. 

First off is Microsoft’s user-centered design prin�

ciples as described in Fundamentals of Designing 

User Interaction: Design Principles and Methodologies 

(1998): 

9

1) User in Control – An important principle of user 

interface design is that the user should always feel in 

control of the software, rather than feeling controlled by the software. This principle has a number 

of implications. 

• The first implication is the operational assump�

tion that the user initiates actions, not the com�

puter or software – the user plays an active, rather 

than reactive, role. You can use techniques to 

automate tasks, but implement them in a way that 

allows the user to chose or control the automa�

tion. 

• The second implication is that users, because of 

their widely varying skills and preferences, must 

be able to personalize aspects of the interface. The 

system software provides user access to many of 

these aspects. Your software should reflect user 

settings for different system properties, such as 

color, fonts, or other options. 

• The final implication is that your software should 

be as interactive and responsive as possible. Avoid 

modes whenever possible. A mode is a state that 

excludes interaction or otherwise limits the user 

to specific interactions. When a mode is the only 

or the best design alternative — for example, for 

selecting a particular tool in a drawing program 

— make certain the mode is obvious, visible, the 

result of an explicit user choice, and easy to 

cancel. 

2) Directness - Design your software so that users can 

directly manipulate software representations of information. Visibility of information and choices 

also reduce the user’s mental workload. Users can 

recognize a command easier than they can recall its 

syntax. Familiar metaphors provide a direct and 

intuitive interface to user tasks. By allowing users to 

transfer their knowledge and experience, metaphors 

make it easier to predict and learn the behaviors of 

software-based representations. Metaphors support 

user recognition rather than recollection. Users remember a meaning associated with a familiar object 

more easily than they remember the name of a 

particular command. 

3) Consistency – Consistency allows users to transfer 

existing knowledge to new tasks, learn new things 

more quickly, and focus more on tasks because they 

need not spend time trying to remember the differ�

ences in interaction. By providing a sense of stabil�

ity, consistency makes the interface familiar and 

predictable. 

4) Forgiveness – Even within the best designed interface, users will make mistakes. An effective design 

avoids situations that are likely to result in errors. It 

also accommodates potential user errors and makes 

it easy for the user to recover. 

5)� Feedback – Always provide feedback for a user’s 

actions. Visual and (sometimes) audio cues should 

be presented with every user interaction to confirm 

that the software is responding to the user’s input 

and to communicate details that distinguish the 

nature of the action. Effective feedback is timely 

and is presented as close to the point of the user’s 

interaction as possible. Even when the computer is 

processing a particular task, provide the user with 

information regarding the state of the process and 

how to cancel that process if that is an option. 

Nothing is more disconcerting than a “dead” screen 

that is unresponsive to input. A typical user will 

tolerate only a few seconds of an unresponsive 

interface. 

6) Aesthetics – The visual design is an important part 

of a software’s interface. Visual attributes provide 

valuable impressions and communicate important 

cues to the interaction behavior of particular ob�

jects. At the same time, it is important to remember 

that every visual element that appears on the screen 

potentially competes for the user’s attention. Provide a pleasant environment that clearly contrib�

utes to the user’s understanding of the information 

presented. 

7) Simplicity – An interface should be simple (not 

simplistic), easy to learn, and easy to use. It must 

also provide access to all functionality provided 

by an application. Maximizing functionality and 

maintaining simplicity work against each other 

in the interface. An effective design balances these 

objectives. One way to support simplicity is to 

reduce the presentation of information to the minimum required to communicate adequately. Irrel�

evant information clutters your design, making it 

difficult for users to easily extract essential informa�

tion. Another way to design a simple but useful 

interface is to use natural mappings and semantics. 

The arrangement and presentation of elements af�

fects their meaning and association. 

10

IBM Corporation (1998) 

IBM’s design principles for ease of use as described 

in What is HCI? (1998), are as follows: 

1) Support: User is in control with proactive assis�

tance. Allow users to be in control of the interface. 

Don’t limit users by artificially restricting their 

choices. 

2)� Familiarity: Build on users’ prior knowledge. Allow 

users to build on prior knowledge, especially knowl�

edge gained from experience in the real world. A 

small amount of knowledge, used consistently 

throughout an interface, can empower the user to 

accomplish a large number of tasks. Concepts and 

techniques can be learned once and then applied in 

a variety of situations. 

3) Simplicity: Don’t compromise usability for func�

tion. A poorly organized interface cluttered with 

many advanced functions distracts users from ac�

complishing their tasks. Keep the interface simple 

and straightforward. 

4) Obviousness: Make objects visible and intuitive. 

Where you can, use real-world representations in 

the interface. Real-world representations and natu�

ral interactions make the interface more intuitive to 

learn and use. 

5) Encouragement: Make actions predictable and re�

versible. A user’s actions should cause the results the 

user expects. To meet those expectations, the designer must understand the user’s tasks, goals, and 

mental model. Even seemingly trivial user actions 

should be reversible. 

6)� Accessibility: Make all objects accessible at all times. 

Users should be able to use all of their objects in any 

sequence and at any time. Avoid the use of modes, 

those states of the interface in which normally available actions are no longer available or in which an 

action causes different results than it normally does. 

7)� Safety: Keep the user out of trouble. Users should be 

protected from making errors. The burden of keep�

ing the user out of trouble rests on the designer. The 

interface should provide visual cues, reminders, lists 

of choices, and other aids. Humans are much better 

at recognition than recall. Contextual help as well as 

agents, can provide supplemental assistance. Users 

should never have to rely on their own memory for 

something the system already knows. 

8) Personalization: Allow users to customize. The in�

terface should be tailored to individual users’ needs 

and desires. In an environment where multiple users 

are sharing a machine, allow the users to create their 

own system personality and make it easy to reset the 

system. In an environment where one user may be 

using many computers, make personalization infor�

mation portable so the user can carry that “person�

ality” from one system to another. 

3.2 Design Process 

Introduction 

The general guidelines given in the previous sec�

tion are used within the context of the user-centered 

design process. A complete description of the issues, 

history, and current models of user-centered design 

processes is outside the scope of this report. The 

reader is referred to How to Design Usable Systems 

(Gould, Boies, Ukelson, 1997), Software – User Interface Design (Liu, 1997), Handbook of Usability Testing (Rubin, 1994), Designing the User Interface 

(Shneiderman, 1992), and Design for Success (Rouse, 

1991) for more in-depth descriptions of the usercentered design process. However, the larger context 

in which the previously mentioned guidelines are to 

be used needs to be described as does the process that 

can help the designer realize their display goals. 

The first section brushes the surface of how and 

why unusable products (including cluttered cockpit 

displays and complex FMSs) and systems continue to 

flourish in the field of computer-based products and 

systems. The second section is a relatively short 

explanation of the user-centered design process, with 

many of the references coming from the previously 

mentioned sources on the process. 

Why are so many computer-based products hard to use? 

1)� “During product development the emphasis and 

focus have been on the machine or system, not on 

the person who is the ultimate end user” (Rubin, 

1994; all following quotes are from this source 

unless identified as otherwise). There are several 

reasons for this. First of all, there has been “an 

underlying assumption that since humans are so 

flexible and adaptable, it is easier to let them adapt 

themselves to the machine, rather than vice versa”. 

After all, the thinking goes, the problem can always 

be solved by training. Secondly, developers, almost 

invariably comprised of engineers, have been “more 

comfortable with the seemingly ‘black and white,’ 

scientific, concrete issues associated with systems, 

than with the gray, muddled, ambiguous issues 

11

associated with human beings.” Finally, developers 

have historically “been hired and rewarded for their 

ability to solve more technical problems, not for 

their ‘human factors’ skills.” 

2) Modern computer-based technology is penetrating 

new markets and workplaces, where the users are apt 

to be less familiar with the technology than the 

designers. The original users of computer-based 

“products shared similar characteristics” with the 

developers. Because of this, the developers practiced 

“next bench” design, a method of designing for the 

user who is literally sitting one bench away in the 

development lab. Needless to say, those days are 

gone. Today’s user is no longer even remotely com�

parable to the designer in skill set, aptitude, expecta�

tion, or in almost any attribute that is relevant to the 

design process. 

3) “The design of usable systems is a difficult, unpre�

dictable endeavor, yet many organizations treat it as 

if it were just ‘common sense.’”. “The trivializing of 

usability creates a more dangerous situation than if 

designers freely admitted that usability was not their 

area of expertise, and began to look for alternative 

ways of developing products”. Usability principles 

are not obvious, and there is a “great need for 

education, assistance, and a systematic approach in 

applying so-called ‘common sense’ to the design 

process.” After all, if it were just “common sense”, 

then usable systems and products also would be 

common. 

4) “The design of the user interface and the technical 

implementation of the user interface are different 

activities, requiring very different skills”. Today, the 

emphasis and need has shifted more on the design 

aspect, while many engineers possess the mind set 

and skill set for tecÈs:hnical implementation. 

“It is easy for designers to lose touch with the fact 

that they are not designing the product, but rather the 

relationship between the product and the human..” In 

designing this relationship, “the designers must allow 

the human to focus on the task at hand, and not on the 

means with which to do that task.” 

“What is needed are methods and techniques to 

help designers change the way they view and design 

products – methods that work from the outside-in, 

from the user’s needs and abilities to the implementa�

tion of the product. The name to this approach is usercentered design.” 

User-Centered Design 

Woodson (1981) defined user-centered design 

(UCD) as “ the practice of designing products so that 

users can perform required use, operation, service, 

and supportive tasks with a minimum of stress and 

maximum of efficiency.” UCD involves the design 

from the human-out and implies that a designer 

should make the design fit the user. Rubin stated that 

“UCD represents not only the techniques, processes, 

methods, and procedures for designing usable prod�

ucts and systems, but just as important, the philoso�

phy that places the user at the center of the process.” 

(Rubin, 1994). 

There are many different ways to divide and arrange 

the design steps within the process. Hewlett Packard’s 

design phase grouping is a typical arrangement. 

• Phase 1. Needs Analysis 

• Phase 2. Requirement Specification 

• Phase 3. Conceptual Design 

• Phase 4. Prototype, Development, and Test 

• Phase 5. Product Evaluation 

Phase 1. Needs Analysis 

Gould et al. (1997) call this phase the “GearingUp Phase.” This is mainly an information gathering 

phase. The objective is to identify the need for the 

product by studying user, task, and work environ�

ment characteristics. Activities include learning about 

related systems, familiarizing yourself with standards 

and guidelines. Identifying and analyzing user tasks. 

Identifying usability problems on similar or existing 

products (Gould et al., 1997; Rubin, 1994). 

Phase 2. Requirement Specification 

Liu (1997) describes the purpose of this phase as 

being to identify the required functions of the interface and a functional specification of what the interface should do. Gould et al. (1997) emphasize the 

need to make “preliminary specifications of the user 

interface, drawing upon existing and leading systems, 

standards, guidelines, and user interface styles where 

appropriate.” Rubin (1994) also describes the need 

for a literature review of Human Factors standards, 

while Smith and Mosier (1984) speak of the need for 

specific design rules to be established during this 

phase. This is begun with a review of the general 

guideline material. Certain guidelines might be dis�

carded as being irrelevant to the particular system. 

Other guidelines might be modified or expanded 

upon. The documentation of these guidelines ensues, 

12

with periodic reviews and revisions as the design 

process continues. 

Phase 3. Conceptual Design 

Hewlett Packard (cited in Rubin, 1994) describes 

the objective of this phase as the “development of 

product specifications to meet previously identified 

requirements and performance objectives.” “Alterna�

tive interfaces as candidates for final design are gen�

erated.” (Liu 1997). The integration of Human 

Factors principles and guidelines takes place in Phase 

3 (Rubin, 1994). 

Phase 4. Prototype, Development, and Test 

This is an iterative phase in which the product is 

tested with the target user population performing 

representative tasks. Although many people prefer to 

“get it right” with the first try, iteration is the norm 

rather than the exception in design (Liu 1997). Or as 

Gould et al. (1997) put it, “User testing and iterative 

design will probably always be necessary to be sure 

that you did get it right the first time. Even expert 

bridge players do not always make their bids.” 

Phase 5. Product Evaluation 

This consists of verifying that the product meets 

the previously defined customer needs, and includes 

on-site customer evaluations conducted to gain use�

ful data for the next generation products. 

The process of user-centered design will help the 

display designer create a usable system – a system that 

is easy to learn, easy to use, contains the right func�

tions and the proper displays. Design guidelines 

themselves will not assure a well-designed system. 

However, the correct implementation of these guidelines within the user-centered design process will. 

3.3 Generalizing From Applied Research 

Before the presentation of the various MFD avia�

tion issues and the related research findings are given, 

the appropriateness and the usefulness of generaliz�

ing from past studies to a particular application is 

discussed. These studies are collectively described as 

“applied research.” The guidelines mentioned in the 

previous section are not of this “type.” Instead, they 

are “findings that apply or are valid over a wide range 

of situations” (Chapanis, 1990), and are often derived through what has commonly been termed “ba�

sic research.” 

In his 1990 paper, “Some Generalizations about 

Generalization,” Chapanis defined generalizing as 

“extrapolating to conditions not identical to those at 

the time original observations were made – to other 

groups of people, to other variations of independent 

or dependent variables, to modifications of variables 

that were originally held constant, or to other envi�

ronments.” 

To take an excerpt from this Chapanis paper, the 

philosopher David Hume (see Lindsay, 1911) wrote, 

in A Treatise on Human Nature, in 1739: 

Our foregoing method of reasoning will easily 

convince us, that there can be no demonstrative 

arguments to prove, that those instances of which we 

have no experience resemble those of which we have 

had experience...We suppose, but are never able to 

prove, that there must be a resemblance betwixt those 

objects, of which we have had experience, and those 

which lie beyond the reach of our discovery. 

This dismaying point of view has been echoed 

more recently by experts such as Fromkin and Streufert 

(1976): 

Although it is important to determine if a relationship 

is relevant outside the confines of a particular laboratory 

experiment, generalizations are never logically justified 

and, to further complicate the issue, there are no 

objective criteria which yield unequivocal answers to 

the question of generality. 

The belief that findings can be generalized is 

widely accepted throughout the scientific commu�

nity. According to Chapanis (1990), “It lies at the 

heart of all science and governs the way we live.” 

Perhaps the best evidence can be found from the 

studies of conditioning, behavior modification, and 

transfer of training. These all tell us that people will 

react or perform in essentially the same way for a range 

of similar conditions. A human factors study is basically 

a simulation in which certain kinds of behavior are 

observed. It follows, then, that the closer the research 

situation matches the real one, the more justified we are 

in generalizing from the empirical findings to what 

would happen in a real environment (ibid). 

The key word is “similarity.” The appropriateness 

in generalizing increases the more closely the simula�

tor or experiment matches the real operating system. 

Therefore, it is the studies in which the subjects, 

apparatus, tasks, dependent variables, and the test 

environment match those of the application as closely 

as possible that are valued (ibid). 

13

And finally, again from Chapanis: 

It’s easy enough to say that research studies should 

simulate closely the situations to which they are to be 

extrapolated, but the rule is difficult to apply because 

we have no way of measuring similarity or of knowing 

how similar is similar enough. Although attempts have 

been made to formulate general laws, they are still much 

too theoretical and apply to too restricted situations to 

be of use to the human factors practitioner. Under the 

circumstances, we have to fall back on the experience, 

sophistication, and good judgement of the investigator. 

Familiarity with the literature and experience with what 

works and what does not work are invaluable aids to 

the investigator in deciding how similar is similar 

enough. 

With this cautionary note, the following sections 

discuss many of the issues and results of “applied 

research” work that can be related to MFD design. 

4. HUMAN FACTORS GUIDELINES 

DERIVED FROM RESEARCH 

4.1 Air Traffic Displays 

Depth Cues as Traffic Display Aids 

Background 

“Current aircraft cockpits using multifunction 

displays present the pilot with two-dimensional 

representations of the three-dimensional environment. 

The pilot must take the information from the twodimensional displays and construct a representational 

three-dimensional world” (Mazur & Reising, 1990). 

Three-dimensional displays have their drawbacks, 

though. Depth is often difficult to judge, and line-ofsight problems are more likely to exist. Accordingly, 

many applied research studies have not found that 

these seemingly more intuitive displays enable supe�

rior pilot performance. 

With the hopes of alleviating some of the drawbacks of a 3D display, depth cues can be included 

into the display. These cues can include stereoscopic 

3D, familiar size, and aerial perspective. 

Stereoscopic 3D is a true binocular cue to depth. 

It involves “simultaneously viewing the display from 

two slightly different advantage points and perceptu�

ally blending these two distinct perspectives into a 

unitary mental representation of the external world” 

(Spain, 1982). 

Familiar size is a size cue aid in which the symbol 

size shrinks to represent objects that are further away. 

Aerial perspective incorporates a format in which 

the symbol becomes grayer and less bright as a func�

tion of the object’s distance. 

General Description 

The depth cues help convey spatial location infor�

mation about other aircraft within the volume of 

airspace shown on a display. In general, the more 

depth cues presented to the viewer, the better. The 

majority of the benefit from the depth cues can be 

realized with only two cues (Figures 1,2). In addition, 

there was not a significant difference related to which 

two of the three depth cues were combined. 

Guidelines 

Since aerial perspective and size cueing are easier 

to implement, require less hardware, and would not 

interfere with any non-3D displays, it is recom�

mended that these two depth cues be used in traffic 

displays. 

Figure 1. Average reaction time as a 

function of depth cues. 

2 

3 

4 

5 

6 

Zero One Tw o Three 

Number of depth cues 

Reaction time (sec) 

Figure 2. Average error as a f unction of 

depth cues. 

0 

0.25 

0.5 

0.75 

1 

1.25 

1.5 

Zero One Tw o Three Number of depth cues 

Average error 

14

 Constraints or Comments 

One of the studies was conducted as a relatively 

dynamic fighter mission with Air Force personnel 

(ref. 2). 

A visual search task in which the pilots identified 

the number of aircraft in a particular quadrant was 

conducted (ref. 1,2). 

Key References 

1. Mazur, K. & Reising, J. (1990). The Relative Effec�

tiveness of Three Visual Depth Cues in a Dy�

namic Air Situation Display. In Proceedings of the 

Human Factors Society 34th Annual Meeting, pp. 

16-20. Santa Monica, CA: HFS. 

2. Zenyuh, C., Reising, J., Walchli, S. & Biera, D. 

(1988). A Comparison of a Stereographic 3-D 

Display versus a 2-D Display. In Proceedings of the 

Human Factors Society 32nd Annual Meeting, pp. 

53-7. Santa Monica, CA: HFS. 

Color-Coded Traffic Information 

Background 

“The effective use of cockpit displays of traffic 

information is largely dependent upon the degree to 

which vertical status and trend information can be 

presented simply and unambiguously to the pilot” 

(Beringer et al., 1993). 

Beringer goes on to say that the more “traditional 

use of plan-view displays has been challenged by 

other representations.” Further, although 3D dis�

plays may be very useful, “they suffer from potential 

overlaid symbology causing obscuration or clutter 

along specific viewing vectors.” The article continues 

that an alternative approach is to “use color coding 

techniques to represent vertical trend information in 

a plan-view horizontal situation display.” 

General Description 

Color-coding schemes can facilitate processing of 

the displayed information and can be an aid in the 

pilot’s cognitive tasks. For instance, color has proved 

effective where a great deal of information must be 

presented in a dense format (Kopala, 1979). Maps 

also benefit from the broad categorization powers of 

color. Specifically, “color can be used to separate and 

contrast different elements in a display that cannot be 

separated properly by space – thereby improving 

symbol visibility. In this capacity, color serves as an 

attention cue for the operator.” (Stokes & Wickens, 

1988). “One of the best demonstrated uses of color 

coding is for search tasks where color serves as a 

primary or redundant cue” (Christ, 1975). 

For both a 3D and a 2D display of traffic infor�

mation, the use of color aids in classifying and re�

sponding to other aircraft based on their altitude in 

relation to one’s ownship. Research results indicate 

that color can aid in providing altitude information 

within a cockpit display of traffic information. Not 

only are possible threats identified more quickly, but 

also with fewer errors (Figures 1,2). Guidelines 

Incorporate the use of color as a redundant aid in 

the presentation of altitude data within a traffic 

display. 

If the color coding pertains to altitude, it should 

depend on the altitude in relation to the ownship -

not to the ground. 

The color coding should be consistent and should 

follow current stereotypes (see ref. 1).Constraints 

Simplified tasks were carried out to examine the 

merits of color-coding. 

No other displays or color interference from other 

displays were simulated. 

4 

5 

6 

7 

8 

9 

Color-coded 

display 

Numeric display 

Figure 1. Mean response time for 

different information coding. 

Mean response time (sec) 0 

1 

2 

3 

4 

5 

Color-coded 

display 

Numeric display 

Figure 2. Threat classification errors 

for different information coding. 

Threat classification errors (%) 

15

Key References 

1. Beringer, D., Allen, R., Kozak, K., & Young, G. 

(1993). Responses of Pilots and Nonpilots to 

Color-coded Altitude Information. In Proceedings of the Human Factors and Ergonomics Society 

37th Annual Meeting, pp. 84-87. Santa Monica, 

CA: HFES. 

2. Burnett, M. & Barfield, W. (1991). Perspective 

versus Plan View Air Traffic Control Displays” 

Survey and Empirical Results. In Proceedings of 

the Human Factors Society 35th Annual Meeting, 

pp. 87-91. Santa Monica, CA: HFS. 

3. M Christ, R. (1975). Review and Analysis of Color 

Coding Research for Visual Displays. Human 

Factors, 17(6), pp. 542-570. 

4. Kopala, C. (1979). The Use of Color-Coded Sym�

bols in a highly Dense Situation Display. In 

Proceedings of the Human Factors Society 23rd 

Annual Meeting, pp. 397-401. Santa Monica, 

CA: HFS. 

5. Krebs, M.J., Wolf, J.D., and Sandvig, J.H. (1978). 

Color display design guide. Office of Naval Research: Final Report ONR-CR213-136-2F. 

4.2 Weather Displays 

Rotating Versus Fixed Weather Displays 

Background 

With the latest generation of supercomputers, 

newly installed weather observing systems, high speed 

data communications, and modern computer-gener�

ated graphics, it is now possible to present weather 

forecast information in a format that meets user’s 

needs (U.S. GAO, 1993). The integration and pre�

sentation of the weather data raises the question as to 

what type of display should be used – Rotating or 

Fixed. 

When using a paper map, a user has the option of 

either orienting the map with the northerly direction 

upward (north-up, fixed map) or rotating the map to 

align the direction of travel upwards (track-up, rotat�

ing map). 

The fixed map requires the user to mentally rotate 

the map to have the stationary world-referenced 

frame (WRF) of the map, correspond with the egoreferenced frame (ERF) of the world seen through the 

cockpit glass. 

Since a rotating map always corresponds with the 

view of the world that the pilot sees, the need for the 

mental rotation can be eliminated with this type of 

map. In addition, since the rotating map corresponds 

to the pilot’s view, this is the type of map that follows 

Roscoe’s principle of pictorial realism. That is, that 

the display should be compatible with the view that 

the user experiences. On the other hand, the fixed, 

north-up map provides a constant frame of reference 

to the user. This enables one to better learn world 

features and create a mental model of the 

environment.General Description 

Rotating maps are considered superior for naviga�

tional tasks, while fixed maps better support tasks 

that require global situational awareness. These are 

duties that require the pilot to know where they are 

“with regards to features and landmarks on the ground 

and in a much broader volume of airspace” (Wickens, 

1992). 

Rotating maps led to better performance in navi�

gating around the weather. (See Figures 1 and 2). 

30 

31 

32 

33 

34 

35 

Fixed Rotating 

Figure 1. Radial distance traveled for 

display type. 

Distance (miles) 

0.2 

0.21 

0.22 

0.23 

Fixed Rotating 

Figure 2. Probability of cloud penetration. 

"Collision" percentage 

16

Guidelines 

• A rotating, track-up display should be used for the 

presentation of weather information. Constraints 

and Comments 

• Student pilots were used (ref. 1).


• The sole task was to navigate around a weather


problem (ref. 1). 

• The 2D display contained 2 views simultaneously – 

a planar and a profile view (ref. 1). 

Key References 

1. Boyer, B. & Wickens, C. (1994). 3D Weather Displays for Aircraft Cockpits. ARL-94-AA/NASA94-4. NASA Ames Research Center. Moffett Field, 

CA. 

2. Wickens, C. (1992). Engineering Psychology and Human Performance. New York: Harper Collins Pub. 

4.3 Navigation Displays 

Navigation Display Integration 

Background 

Nowhere has automation been used more effec�

tively than in aircraft navigation displays. Glass cockpit navigation displays are a radical departure from 

their electromechanical predecessors. All aircraft 

manufacturers have integrated information formerly 

presented on electromechanical instruments into a 

single plan view map display to which has been added 

other features derived from the flight management 

system database. Terrain detail, explicit location of 

ground navigation aids and pilot-constructed 

waypoints, airport locations, and other data can be 

portrayed together with the programmed route (Bill�

ings, 1997). 

• Because of the recent advances in GPS and comput�

ing capabilities, issues are now raised concerning 

exactly how, or even if, terrain, traffic, and weather 

information should be integrated into the navigation 

display.General Description 

• Surveys of pilots’ opinions on what information 

should be incorporated into the navigation display, 

and preliminary studies have found that, for example, pilots perform better with traffic and weather 

displays integrated onto the navigation display (Fig�

ures 1, 2).Guidelines 

• Primary navigational aids, intersections, and airports 

should be displayed symbolically with identifying 

labels for intermediate map scales only. 

• Airport control zones, taxiways, and small airports 

should not be displayed. 

• Terrain information should be displayed automati�

cally if an aircraft was below the minimum safe 

altitude (MSA), and should also be available at pilot 

request. 

• The majority of airline pilots did not want weather 

information included on CDTI (Hart & Loomis, 

1980). Another survey, however, suggested that the 

pilots do want weather integrated on the navigation 

display (Hart & Loomis, 1980). Both groups agreed 

that if weather is incorporated into another display, 

it should be initiated by the pilots rather than occurring automatically. 

• The display of other aircraft should be limited to 

those nearest the ownship. One survey suggested 

displaying only those aircraft that are within ± 2000 ft. 

• Commercial pilots also wanted to know whether 

another aircraft was flying under visual or instrument 

flight rules to be displayed digitally or coded into the 

symbol, and should only be displayed at the pilots 

request. 

Figure 1. Traffic conflicts as a function of 

display dimension and integration. 

10 

15 

20 

25 

30 

35 

40 

2D 3D Dimension 

Traffic conflicts (%) 

Separated 

Integrated 

Figure 2. Weather conflicts as a function 

of display dimension and integration. 

2 

4 

6 

8 

10 

12 

2D 3D Dimension 

Weather conflicts (%) 

Integrated 

Separated 

17

• A coplanar navigation display is recommended that 

includes both weather and traffic information. 

• The capability to turn on or off the overlaid terrain, 

traffic, or weather data is recommended. Except for 

the instances when minimum safe altitudes or dis�

tances are violated, the displays should not be intro�

duced or removed automatically. 

Constraints 

• Little research has been done to determine what 

information should be displayed in conjunction with 

the navigation display. 

Key References 

1. Hart, S. & Loomis, L. (1980). Evaluation of the 

potential format and content of a cockpit display 

of traffic information. Human Factors, 22(5), pp. 

591-604. 

2. O’Brien, J. & Wickens, C. (1997). Cockpit displays of 

traffic and weather information: Effects of dimension and data base integration. Technical Report 

ARL-97-3/NASA-97-1. Aviation Research Labo�

ratory. University of Illinois at UrbanaChampaign. 

Rotating versus Fixed Navigation Displays 

Background 

When using a paper map, a user has the option of 

either orienting the map with the northerly direction 

upwards (north-up, fixed map) or rotating the map in 

such a way as to constantly align the direction of 

travel upwards (track-up, rotating map). Similarly, 

an electronic navigational map can be displayed ei�

ther way. 

The rotating map would seem to enable superior 

pilot performance by presenting an inside-out or egocentered representation of the environment. This 

design follows the principle of pictorial realism in 

that it represents an “out the window” view. However, there is some reason to believe that a track-up 

map may violate the pilot’s mental model of the 

motion relationship, in which it is the aircraft not the 

environment that is moving. 

General Description 

Different tasks require different map orientations. 

North-up maps have been found superior in landmark searching tasks, and for pilot communication 

with other aircraft. Both of these tasks are best served 

with a consistent location of landmarks (a stationary 

world), that is afforded by the north-up map. Wickens 

(1992) has described these types of tasks as “global 

situation awareness” tasks. These are duties that require aviators to know where they are with regard to 

features and landmarks on the ground and in a much 

broader volume of airspace. 

On the other hand, local guidance tasks seem to be 

performed best with the track-up display. These are 

tasks in which the pilot needs to know when to climb, 

descend, accelerate, or decelerate to follow the appro�

priate path. 

A track-up map is the better choice for navigation 

displays. Indeed studies have shown that, not only do 

pilots prefer the track-up navigation display, but that 

they also perform better with it (Figure 1). 

Guidelines 

• The navigation display should be presented in a 

rotating, track-up format. 

Constraints and Comments 

• The empirical results were somewhat mixed (Refs. 

1, 2). 

• The consistency between displays (i.e. whether the 

displays are all one type or if there is a mixture) is 

important (ref. 1). 

• Widely varying navigational screens were used in the 

three referenced studies. 

Key References 

1. Andre, A., Wickens, C., Moorman, L., & Boschelli, 

M. (1991). Display Formatting Techniques for 

Improving Situation Awareness in the Aircraft 

Cockpit. The International Journal of Aviation 

Psychology, 1(3), pp. 205-218. 

2 

2.5 

3 

3.5 

4 

Track-up North-up 

Figure 1. Mean navigation response 

time as a function of map type. 

Me

an r

esp

onse time (sec) 

18

2. Aretz, A.J. (1991). The Design of Electronic Map 

Displays. Human Factors, 33(1), pp. 85-101. 

3. Harwood, K. & Wickens, C. (1991). Frames of 

Reference for Helicopter Electronic Maps: The 

Relevance of Spatial Cognition and Componen�

tial Analysis. The International Journal of Aviation 

Psychology, 1(1), pp. 5-23. 

3D Display Elevation Angle 

Background 

With the recent advances in technology, the utiliza�

tion of 3D displays in the cockpit has received some 

attention in the research literature. Many applied research studies have been conducted to access the worth 

of the various designs and ultimately, make design 

recommendations. 

One aspect of the 3D display that has not received 

much attention is the question of the optimum eleva�

tion angle for the 3D display. Differences in elevation 

between a map and a pilot’s forward field of view 

(FFOV) are known to effect the efficiency in 3-dimensional image comparisons. “Such would be the case 

when flying with a 90 degree (top-down) map and an 

FFOV that is inherently 3-dimensional and something 

less than 90 degrees.” (Hickox & Wickens, 1997). 

Part of the cost associated with a 3D display is the 

required mental rotation that the viewer must complete 

to have the display “line up” with the view of the world 

available to them out the window. Studies have found 

that the response time costs associated with elevation 

angle is not a linear effect (Hickox & Wickens, 1997). 

This result is a departure from the linear relationship 

normally associated with 2D mental rotation. 

General Description 

Past research has not developed a formula that can 

adequately predict pilot response times based on the 

angular disparity between the FFOV and the Map 

display. The Hickox and Wickens study (ref. 3) predicts 

response time not as a function of the difference between the map and FFOV, but between the absolute 

value of the sine difference of the map and FFOV. This 

response time data, combined with the accuracy data 

and the Yeh and Silverstein (1992) data, suggest that 

the optimal elevation angle for the map display is 45 

degrees. 

Guidelines 

• If a 3D perspective display map is to be used, the 

elevation angle should be close to 45 degrees. 

Constraints 

• An image comparison test was conducted (ref. 3). 

•� There was only a small decrease in performance for 

angles of elevation slightly lower than 45 degrees 

(ref 3). 

Key References 

1. Aretz, A., & Wickens, C. (1992). The mental rota�

tion of map displays. Human Performance, 5(4) 

pp. 3-28. 

2. Eley, M. (1988). Determining the shapes of land 

surfaces from topographic maps. Ergonomics, 31, 

pp. 355-76. 

3. Hickox, J. & Wickens, C. (1997). 3-D Electronic 

Maps, Design Implications for the Effects of 

Elevation Angle Disparity, Complexity, and Fea�

ture Type. In Proceedings of the Human Factors 

and Ergonomics Society 41st Annual Meeting, pp. 

23-27. Santa Monica, CA: HFES. 

4. Yeh, Y-Y, & Silverstein, L. (1992). Spatial judge�

ments with monoscopic and stereoscopic presen�

tation of perspective displays. Human Factors, 34, 

pp. 583-600. 

Taxiway navigation maps: HUD and 3D vs. 2D 

Background 

Major automation projects are currently underway 

to increase the efficiency and safety of airborne traffic. 

Improvements have already been realized in supporting 

low-visibility landings as a result of the technological 

improvements (Lasswell & Wickens, 1995). However, 

these improvements will be lost without similar im�

provements in ground traffic flow. “A pilot who successfully completes a mission and lands in zero-visibility 

conditions will be faced with the daunting task of rolling 

off the runway and maneuvering to the terminal with 

little or no visual cues” (Lasswell & Wickens, 1995). 

Recent mishaps involving runway deviations and 

“ground traffic collisions further highlight the need for 

improved methods” (Lasswell & Wickens, 1995). 

Regardless of the technology to be used in supporting 

the pilot, a central issue still concerns the interface 

between the technology and the user. “The display must 

enhance the pilot’s situation awareness, while mini�

mally interfering with the taxiing task” (Lasswell & 

Wickens, 1995). The question of whether to present the 

map and the route guidance in a head-up or head-down 

fashion, and in a 3-D or 2-D view is directly related to 

this issue. 

19

Presenting information head-up provides the poten�

tial benefits of reducing the scanning distance between 

the display and the scene out the window, and reducing 

the accommodation changes necessary to switch between the two domains. These advantages are countered 

by the problems of clutter resulting from the overlapping images and the problem of cognitive capture. 

Placing information within an operator’s forward field 

of view may create an involuntary attraction of attention 

to the HUD, even when there is no need for it 

Similarly, the effectiveness of 3-D displays may actu�

ally suffer as a result of their more realistic presentation 

of the environment. For instance, 3-D displays intro�

duce a degree of ambiguity regarding the precise loca�

tion of points along the line of sight, and limitations 

arise from the limited field of view allowed by an 

egocentric display.General Description 

The use of a HUD is advantageous for tracking tasks. 

Also, average taxi speed was increased when information 

was presented in the head-up location (Figure 1). 

It appears that superimposing the route guidance 

information on the out-the-window scene allowed the 

pilots’ attention to remain outside. They maintained 

faster taxi speeds while still being confident that they 

could detect and respond to unplanned outside events. 

In addition, pilots indicated a preference for the HUD. 

For panel displays, there has been mixed results 

concerning the 3-D vs. 2-D issue for taxiing. Results 

indicate that reacting to unplanned ground traffic is 

more difficult with the 2-D display (Figure 2). Presum�

ably, the difficulty arises because of the greater process�

ing demands imposed by the 2-D display. 3-D displays 

have supported better (or equal) tracking perfor�

mance with no shortcomings related to unplanned 

event detection. 

Guidelines 

• Utilize a HUD for taxiway navigation. 

•� The taxiway navigation display should be a 3-D 

display. 

•� Only information critical to the task should be 

presented on the display. 

Constraints and Comments 

•� There is a limited amount of research on the benefits 

of taxing with HUDs. 

•� The HUDs in these studies were relatively unclut�

tered. If the HUDs presented more information, 

then the performance advantages of the HUD and 

the 3-D display might diminish. 

Key References 

Lasswell, J. & Wickens, C. (1995). The Effects of Display Location and Dimensionality on Taxi-way 

Navigation. ARL-95-5/NASA-95-2. University of 

Illinois at Urbana-Champaign Technical Report. 

Aviation Research Laboratory. 

Weintraub, D., & Ensing, M. (1992). Human Factors 

Issues in Hhead-Up Display Design: The Book of 

HUD. State-of-the-art-report, Crew System Er�

gonomics Information Analysis Center, WrightPatterson AFB, Dayton, OH. 

Wickens, C., Liang, C., Prevett, T., & Olmos, O. 

(1994) Egocentric and exocentric displays for terminal area navigation. (Tech. Rep. No. ARL-94-1/ 

NASA-94-1). Savoy: University of Illinois, Avia�

tion Research Lab. 

14.2 

14.4 

14.6 

14.8 

15 

15.2 

15.4 

Head-up Head -down 

Figure 1. Average taxi speeds for 

display locations. 

Average speed (knots) 

60 

70 

80 

90 

100 

2D 3D 

Figure 2. Runway incursions versus 

display type. 

Runway incursions detected (%) 

20

4.4 MFD Menu Organization 

Introduction to Multifunction Display Menus 

Background 

“The development of increasingly capable com�

puters and software tools, and advances in the design 

of displays has provided the technology for the evo�

lution of the multifunction display (MFD)” (Francis, 

1998). These advances permitted replacing the mul�

titude of separate status, warning, and control devices with an integrated MFD. Since the inception of 

the MFD, crewmembers have pushed buttons to 

navigate through a hierarchy of display pages con�

taining instructions, information, or lists of useractivated functions (Francis, 1998). 

“MFDs have generally been credited with reduc�

ing cockpit instrument ‘clutter’ as well as reducing 

the time crewmembers spent searching for, and mentally integrating aircraft information” (Francis, 1998). 

The reduction in pilot workload due to the introduc�

tion of the MFDs was a primary factor in eliminating 

the need for flight engineers. However, with time, 

any reduction in workload was gradually offset by the 

tendency for MFDs to embody an increasing number 

of features and functions. This situation is similar to 

today’s home computer. Today’s computer is much 

more powerful than earlier versions, but since the 

number of functions has also expanded proportionally, it has become no easier to use. As a matter of fact, 

in the aviation world, there have been claims and 

instances were the workload with the current stateof-the-art MFD has actually been greater than with 

the less sophisticated systems (Francis, 1998). 

In effect, MFDs “trade the workload associated with 

a visual search of the cockpit instruments for a cognitive 

workload associated with a search through mental im�

ages of a multidimensional database of pages” (Francis, 

1998). The following sections describe many of the 

issues and research findings that can be used to aid in the 

design of these MFDs. 

Key References


Francis, G. (1998). Designing Optimal Hierarchies for


Information Retrieval with Multifunction Displays. 

U.S. Army Aeromedical Research Laboratory. Fort 

Rucker, Alabama. USAARL Report No. 98-33. 

MFD Menu Organization 

Background 

The majority of MFDs incorporate hierarchical struc�

tures that define organization of content and naviga�

tional paths between display pages or modes. Navigation 

through the hierarchy is accomplished by the use of 

navigational objects such as menus, lists, and soft or 

hard keys. The user begins at the top page and then, 

through the activation of the keys or buttons, completes 

a sequence of selections that ultimately leads to the 

target selection/page (Francis & Reardon, 1997, Papp 

& Cooke, 1997). 

“Despite the popularity of menu selection as a form 

of user-computer dialogue, until recently, very little has 

been known about the potential effects of menu struc�

ture on operator performance.” (Snowberry, Parkinson, 

& Sisson, 1983). “In most interactive systems employ�

ing menu selection the number of items is far too great 

to list in a single display. Menu hierarchies can be 

arranged with many items on a menu and a minimum 

number of sequential menus (breadth) or with few lines 

on each menu and several levels (depth).” (Snowberry, 

Parkinson, & Sisson, 1983). 

For many applications, the decisions to use breadth 

or depth in menu construction has been based on 

guesses about user characteristics rather than on data 

obtained from empirical studies. Many efforts have 

been completed in this area, and the research results 

have yielded general guidelines about the appropriate�

ness of different organizations. (Seidler & Wickens, 

1992). 

Key References 

Francis, G. & Reardon, M. (1997). Aircraft Multifunc�

tion Display and Control Systems: A New Quan�

titative Human Factors Design Method for Orga�

nizing Functions and Display Contents. USAARL 

Report No. 97-18. U.S. Army Aeromedical Research Laboratory. Fort Rucker, Alabama. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., and Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Seidler, K.S. & Wickens, C.D. (1992). Distance and 

Organization in Multifunction Displays. Human 

Factors, 34(5), pp. 555-569. 

Snowberry, K., Parkinson, S. & Sisson, N. (1983). 

Computer Display Menus. Ergonomics, 26(7), 

pp. 699-712. 

21

Depth versus Breadth in MFD Menus 

Background 

“The majority of menus are organized into a hier�

archical tree, in which each menu panel in the hierar�

chy can be reached only” (Paap & Cooke, 1997) from 

a single node that lies directly above it. “Depth (d) is 

usually defined as the number of levels in the hierar�

chy. Breadth (b) is defined as the number of items or 

choices within each menu panel” (Paap & Cooke, 

1997). 

A structure with several layers of depth requires the 

user to either discover or recall how to get from where 

they are to where they want to go. These navigational 

requirements become “more and more treacherous as 

the depth of the hierarchy increases” (Paap & Cooke, 

1997). 

On the other hand, there are reasons for consider�

ing a system with greater depth. The obvious reason 

is crowding. The available space on the panel, and the 

required amount of space for the names and/or de�

scriptors may require the need for more depth. Another attractive feature associated with depth is 

funneling. Funneling refers to a “reduction in the 

total number of options processed that can be achieved 

by designing a system where greater depth is traded 

for less breadth” (Paap & Cooke, 1997) – especially 

when the processing time per option is long. To 

clarify, consider a database with 64 options. If all the 

items appear as choices in a single panel, then an 

exhaustive search would lead to 64 options being 

processed. The other extreme would be to maximize 

depth and minimize breadth (d=6, b=2). An exhaus�

tive search of both options on each of the six succes�

sive panels would entail only 12 options (Paap & 

Cooke, 1997). 

As depth increases, the number of options to be 

processed decreases, but the number of panel transac�

tions increases. “Each of the additional panels created 

by the increased depth requires one more response 

(e.g. key press, mouse selection) and one more re�

sponse from the computer” (Paap & Cooke, 1997). 

For the example given above, the maximum depth 

organization would have six times the response-ex�

ecution time compared with the single-panel case. 

General Description 

Lee and MacGregor (1985) proposed a quantita�

tive method to estimate and then minimize the Total 

Search Time (TST) for the task. The formula calcu�

lates the average search time based on depth, breadth, 

processing time per option, human response time, 

and computer response time. For self-terminating 

searches, the formula to determine the optimal num�

ber of items per panel (b) is as follows (with b = 

breadth, k = human response time, c = computer 

response time, t = processing time per option) 

Search time = (bt + k + c)[(log2 N / log2 b)]. 

Depending on the various times, the optimal 

breadth is typically in the range of 4 to 13 items per 

panel. The longer the processing time per option, as 

compared to the execution time of the operator and 

the computer, the lower the optimal breadth will be. 

Guidelines 

• The number of options per panel (breadth) should be 

in the range of 4 to 13. 

• The more demanding the task of processing indi�

vidual options, the lower the breadth should be and 

the greater the depth should be. 

Constraints 

• These studies did not consider grouping as an aid. 

• The menus in these studies were homogenous (each 

panel had the same number of choices and each 

choice had the same depth below it). 

• Novice users were used in some of the studies. 

• “Reasonable” human response times (.5 to 1 second) 

were used. These laboratory times may be different 

than “reasonable” rates in the cockpit. 

Key References 

Francis, G. & Reardon, M. (1997). Aircraft Multifunc�

tion Display and Control Systems: A New Quan�

titative Human Factors Design Method for Orga�

nizing Functions and Display Contents. USAARL 

Report No. 97-18. U.S. Army Aeromedical Research Laboratory. Fort Rucker, Alabama. 

Figure 1. Theoretical times for 64 item menu 

navigation. 

14 

15 

16 

17 

18 

19 

20 

1 5 

breadth 

time (sec) 

2 3 4 6 7 8 9 

22

Lee, E. & MacGregor, J. (1985) Minimizing user 

search time in menu retrieval systems. Human 

Factors, 27 (2), pp. 157-162. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., and Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Varied Breadth in MFD Menus 

Background 

The majority of research on the topic of hierarchy 

depth and breadth concerns hierarchies that are both 

homogeneous and complete. That is, the hierarchies 

have the same number of options in each menu 

(homogeneous) and the same number of menus along 

each branch from top to bottom (complete). 

Two related problems occur as a result of this 

limitation. First, since “in practice it is almost never 

possible to construct the recommended complete 

homogeneous hierarchy, it is not clear which hierar�

chy to choose as the optimal one. For example, if a 

hierarchy consists of 16 terminal options” (Fisher, 

Yungkurth, & Moss, 1990) and the optimal number 

of options per panel is calculated as 8, “it is not 

possible to construct a hierarchy with the recom�

mended breadth because there is not integer value d 

such that 8d

 = 16.” (Fisher, Yungkurth, & Moss, 

1990). One is left to decide which of the many 

possible options is best. 

Secondly, even if the recommended hierarchy is 

possible, there are still many structures that are not 

complete (i.e. same number of menus below each 

branch) but may be more efficient. For example, 

consider a hierarchy with 64 terminal items. “There 

are four complete, homogenous structures that can 

be created” (Fisher, Yungkurth, & Moss, 1990) e.g., 

breadth 64 depth 1, breadth 8 depth 2, breadth 4 

depth 3, and breadth 2 depth 6. However, if one 

allowed the number of options per panel (breadth) to 

“vary between 2 and 64 (and not be kept constant as 

with the heterogeneous case), then it can be shown 

that there are more than a million different possible 

hierarchies. Any one of these hierarchies could be the 

optimal one” (Fisher, Yungkurth, & Moss, 1990). 

This scenario relates to the issue of varying menu 

breadth across the level of depth. For instance, a 256 

item menu could be organized as a decreasing menu 

(8 x 8 x 2 x 2), an increasing menu (2 x 2 x 8 x 8), a 

convex menu (2 x 8 x 8 x 2), or a concave menu (8 x 

2 x 2 x 8) (Paap & Cooke, 1997). Or as was men�

tioned earlier, if the menu does not have to be 

“complete”, it can be any one of thousands of other 

organizations. 

General Description 

Determining which one of the myriad of possible 

menu organizations is best is far from an exact science 

at this time. Much of it depends on questions relating 

to how intuitive, appropriate, and distinctive the 

categorizations are. Grouping is an extremely power�

ful tool and has been shown to aid the user – but only 

if the groupings are appropriate and not contrived. 

That is a judgement that the designer of the specific 

menu will have to make. In general, grouping simply 

for the sake of grouping does not improve the effi�

ciency (Paap & Cooke, 1997). 

As far as the general types of menus (e.g., increas�

ing, decreasing, convex, and concave) is concerned, 

the pattern of depth that best funnels the user to the 

correct terminal panel should determine the optimal 

menu structure. For example, if the user’s goal is 

vague, then two options in the top panel might be 

better than eight because the user is more likely to be 

clear on which of the two they should choose. On the 

other hand, if the target is explicit, then greater 

breadth might be advantageous because 8 choices on 

the top panel will likely be less ambiguous than two 

very general options. 

In other words, if the user has “a clear idea of what 

they are looking for then its best to see ‘all the cards 

laid out on the table in front of them’ as soon as 

possible. This is true because potential errors are not 

caused by their failure to know what they are looking 

for, but rather by their failure to understand the 

organization of the menu.” (Paap & Cooke, 1997). 

Conversely, if they are not sure what will satisfy or 

optimize their needs, “then ‘playing a mini-version of 

twenty questions’ at the top levels (Paap & Cooke, 

1997) may funnel them directly to a target that would 

otherwise be difficult to find. 

Indeed research has shown that for fuzzy targets, 

best performance occurs with the concave, and to a 

lesser degree, the increasing menu. These two panels 

are “bottom-loaded.” That is, they have more breadth 

on the bottom panels and accordingly, the least 

amount of uncertainty across the upper levels (Paap 

& Cooke, 1997). Although the research is not overwhelming, breadth seems to be most advantageous at 

the top and bottom of the menu (concave). 

23

Guidelines 

• Careful consideration must be given to finding ap�

propriate groupings for menu items. Grouping is a 

powerful aid for enabling superior performance. 

• If the target is relatively “fuzzy” to the user, an 

organization with relatively little breadth at the top is 

recommended (i.e. “twenty questions” rule). 

• If the target is much clearer to the user, then greater 

depth is recommended throughout (i.e. “lay out the 

cards” rule). 

Constraints and Comments 

• The optimum menu organization is dependent on 

how well the items lend themselves to being grouped. 

• “Reasonable” human response times (.5 to 1 second) 

were used. These laboratory times may be different 

than “reasonable” rates in the cockpit 

Key References 

Fisher, D., Yungkurth, E., & Moss, S. (1990) Optimal 

menu hierarchy design: syntax and semantics. 

Human Factors, 32(6), pp. 665-683. 

Norman, K. (1991) The Psychology of menu selection: 

Designing cognitive control at the human/computer 

interface. Norwood, New Jersey: Ablex. 

Norman, K. & Chin, J. (1989) The menu metaphor. 

Behavior and Information Technology, 8, pp. 125-

134. 

Papp, K., and Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., & Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Item Selection in MFD Menus 

Background 

“The growing popularity of direct manipulation 

interfaces has resulted in a trend away from menu 

selection via discrete identifiers (i.e. typing in a letter 

or digit that represents an item), and toward menu 

selection via pointing” (Paap & Cooke, 1997). The 

menu items are usually selected by moving a pointer 

to the desired option and then selecting it. Cursor 

keys, joysticks, trackballs, touch screens, pens and 

mice are all examples of the devices used to manipu�

late the on-screen pointer. Knowledge of the merits 

of these various selection devices as they relate to 

MFD menu selection is desired. 

General Description 

The mouse has been found to be more efficient 

than a joystick or cursor keys in a task that had the 

subjects move the pointer over different distances to 

different sized targets (Paap & Cooke, 1997). 

Other studies using a wider range of tasks found 

that the touch panel was superior to keyboard iden�

tifiers and the mouse. No interactions were found 

between the type of selector and the application or 

task type, suggesting that there is a consistent advan�

tage with the touch screen (Paap & Cooke, 1997, 

Karat, McDonald, & Anderson, 1984). 

Guidelines 

•� The use of a touch screen or a selection of buttons on 

the perimeter of the screen should be used in the 

design of the MFD. 

Constraints 

• There was not any physical difficulty in reaching and 

pressing the touch screen in any of these studies, as 

there may be in a dynamic cockpit. 

• None of these studies were in an aviation context. 

• Touch screens and not “screen-perimeter” buttons 

were studied. 

• Test subjects were not pilots. 

Key References 

Card, S., English, W., & Burr, B. (1978) Evaluation of 

mouse, rate-controlled isometric joystick, step 

keys, and text keys for selection on a CRT. Ergonomics, 21, pp. 601-613. 

Figure 1. Average total time of realistic

applications with various selectors.

110

115

120

125

130

135

touch panel keyboard

identifier

mouse

Time (sec) 

24

Karat, J., McDonald, J., & Anderson, M. (1984) A 

comparison of selection techniques: Touch panel, 

mouse, and keyboard. Proceedings of INTERACT 

’84. pp. 149-153. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., and Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Item Organization in MFD Menus 

Background 

Many options have been proposed for the organi�

zation of MFD information. Alphabetical and cat�

egorical are two of the more prevalent choices. 

Additional ways to organize the MFD choices in�

clude frequency of use, ordinal dimension or magni�

tude, and temporal order (Paap & Cooke, 1997). 

There is no single “best” way to organize MFD 

information. It is highly dependent on a variety of 

factors such as the type of data, the size of the lists, the 

familiarity of the user with the data, the affordance 

that the options allow towards being divided into 

distinctive categories, and on any constraints that 

may be imposed regarding the depth and breadth of 

the hierarchy. 

General Description 

General guidelines for the likely organization of 

the menu have been created based on a meta-analysis 

of the research conducted in this area. 

Figure 1 shows the guidelines. The top section 

presupposes that most users will have a specific target 

in mind that is highly likely to match one of the menu 

options. The next question to ask is whether the list 

of options is long or short. Those sets of options that 

have conventional orders are likely to be short and are 

likely to induce strong expectations for the options to 

be displayed in their familiar order. If the list is long, 

alphabetizing the selections may be beneficial. If the 

options can be arranged in categories that are both 

distinct (have little conceptual overlap) and well 

known to the end users, then grouping by category 

may be worthwhile. 

The lower section of Figure 1 applies when users 

have only fuzzy targets in mind. For long lists, group�

ing by category will usually be the best strategy. One 

important exception to this case would be when a 

small subset of the options is selected much more 

frequently than the others. In this case, listing the 

options in decreasing order of frequency may be the 

better arrangement, particularly if the categories would 

not be distinctive or if the users may not be familiar 

with the instances of each category (Paap & Cooke, 

1997). 

Guidelines 

• Use Figure 1 as an aid in menu organization 

decisions. 

Constraints 

• These guidelines are generalizations from specific 

research settings, and may not neces�

sarily relate to the specific menu in 

question. 

• There are many different ways to 

“categorize” menu choices after the 

decision has been made to use a “cat�

egorized” menu order. 

Key References 

Hollands, J.G. & Merikle, P.M. 

(1987). Menu organization and user 

expertise in information search tasks. 

Human Factors, 29(5), pp. 577-586. 

Papp, K., & Cooke, N. (1997) Design 

of Menus in Helander, M., Landauer, 

T., & Prabhu, P. (eds), Handbook of 

Human-Computer Interaction. Elsevier 

Science Pub. pp. 533-572. 

25

Speech-Based Control of MFD Menus 

Background 

Speech recognition is one of the more mature of the 

so-called “non-conventional” or future technologies. 

Improvements in speech recognition algorithms have 

led to the realization of reliable, accurate continuous 

speech recognition. As advances in the field continue, 

speech command will become a common method of 

control i d:nput. An experimental F-16 jet aircraft has 

already been equipped with a limited vocabulary that 

controls the switching of various status information 

(McMillan, Eggleston, & Anderson, 1997). It is only a 

matter of time before commercial aircraft will have voice 

controlled features in the cockpit and the designers will 

have to deal with the human factors associated with such 

technology. 

Some of the proposed advantages of voice control are: 

1) “Voice commands allow for more possible responses 

to be given in a shorter period of time, without 

imposing added time-consuming manual compo�

nents” (Wickens & Carswell, 1997). 

2) “Voice options represent more compatible ways of 

transmitting symbolic or verbal information, than 

can be achieved by manual options” (Wickens, 

Vidulich, & Sandry-Garza, 1984). 

3) “Voice options are valuable in environments when 

the eyes, and in particular the hands are otherwise 

engaged” (Wickens, Vidulich, & Sandry-Garza, 

1984). 

4) The “greatest payoff in task performance speed and 

accuracy is for complex information entry tasks that 

must be performed in conjunction with other manual 

or visual tasks” (Simpson, McCauley, Roland, Ruth, 

& Williges, 1987). 

General Description 

Much research and thought has gone into the design 

of various menu organizations (i.e., categorical, conven�

tional, frequency). These design considerations im�

prove performance especially for the novice user who is 

reasonably experienced with the organization, or when 

the options are infrequently used. In cases, though, 

when the user is extremely familiar with the set of 

options or when the menu items are repeatedly selected, 

identifier entry may be more efficient than manual 

selection. A good example of software taking this into 

consideration is Microsoft Word’s allowance for both 

pointing and using identifier shortcuts for many of the 

menu items. These frequent menu selections are an 

excellent opportunity for the use of voice technology. 

Instead of requiring pilots to manually complete two or 

three menu selections to get to the desired display, a 

voice command shortcut that takes them directly to this 

oft-used display will lessen their workload. Even though 

the technology is implemented as an additional means 

to an end, it is very important that it be extremely 

accurate. If recognition accuracy is not in the high 90% 

range, pilots do not want it. 

Guidelines 

• Use voice command technology for the immediate 

selection of a particular item that may not be cur�

rently on the displayed level. 

• Ensure that the voice recognition rate is at least 98% 

accurate. 

• Immediate feedback should be provided to minimize 

any confusion to the user. 

• The voice controls are supplemental to the tradi�

tional manual methods. 

• A correction or “undo” capability must be provided 

to reduce the consequences of recognition errors. 

Constraints 

The most accurate speech recognition systems are 

user-specific (speaker dependent). There are design 

issues related to the relationship among speaker depen�

dent versus independent systems, training and enroll�

ment time, and performance (recognition accuracy). 

Key References 

McMillan, G., Eggleston, R., & Anderson, T. 1997) 

Nonconventional Controls. In G. Salvendy (ed.) 

Handbook of Human Factors and Ergonomics. New 

York: Wiley and Sons. 729-771. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., & Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. 533-572. 

Simpson, C., McCauley, M. Roland, E., Ruth, J. & 

Williges, B. (1987). Speech Controls and Dis�

plays,. In G. Salvendy (ed.) Handbook of Human 

Factors. New York. John Wiley. 

Wickens, C., & Carswell, M. (1997) Information Pro�

cessing in G. Salvendy (ed.) Handbook of Human 

Factors and Ergonomics. Wiley and Sons. 89-129. 

Shortening Navigational Distance in an MFD Menu 

Background 

“Navigational distance may be thought of as the 

number of steps required to arrive at the destination 

26

screen from any other screen. In the MFD, a step is 

simply a decision followed by a key press” (Seidler & 

Wickens, 1992). There are times when the pilot needs 

to scan between particular displays to make compari�

sons or carry out some sort of integration of informa�

tion. The time and the distance to navigate up, across, 

and down the hierarchy are important considerations. 

The introduction of identifiers to shorten the naviga�

tional distance in an MFD is one way to reduce naviga�

tion time. For instance, if direct access keywords are 

available, the navigational distance between any two 

screens could theoretically be one step away. Naviga�

tional distance also can be reduced by providing an 

option to jump instantly back to the top level or up one 

level (Seidler & Wickens, 1992). 

General Description 

The greater the navigational distance in an MFD, the 

greater the traversal time and the larger the decrement in 

memory accuracy (Figure 1). Both Previous and Main 

buttons were found to aid the users, with the Main 

button aiding the users more than the Previous button. 

The utility of an MFD navigational tool, such as a 

direct access code to any screen, is greatest when used by 

Figure 1. Traversal time as a function of 

number of steps. 

40 

50 

60 

70 

80 

90 

100 

1-3 4-6 7-9 10-12 

number of steps 

time (sec) 

Figure 2. Theoretical relationship between screen 

selection usage and rank (Zipf'slaw). 

0 

25 

50 

75 

100 

0 25 0 5 100 

rank order of screen 

frequency of screen use 

5 7

pilots who are very familiar with the accessed screen. 

Voice control is one design option for a navigation tool. 

In many communication environments, the most 

frequently used word, screen, or web page occurs much 

more often than the second most, the second much 

more often than the third, and so forth. This is referred 

to as Zipf’s law (Zipf, 1949). That is, the frequency with 

which selections are used is a negative power function of 

their rank (figure 2). Individual pilots are likely to have 

a few screens that they call up much more frequently 

than others. The access code for these select, few screens 

will be most valuable to the pilot. Therefore, there may 

not be a requirement for the pilots to complete the 

cognitively demanding task of learning display access 

names for a large number of screens. 

Guidelines 

• Include both a Previous and a Main button to help 

the pilot navigate. 

• Provide direct access to all displays by entering an 

appropriate key word (or voice command). 

Constraints 

• The number of buttons and the design of the MFD 

varied considerably in the studies. 

Key References 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., & Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. 533-72. 

Seidler, K.S. & Wickens, C.D. (1992). Distance and 

Organization in Multifunction Displays. Human 

Factors, 34(5), 555-69. 

Wickens, C., & Carswell, M. (1997) Information Pro�

cessing in G. Salvendy (ed.) Handbook of Human 

Factors and Ergonomics. Wiley and Sons. 729-71. 

Category Organization in an MFD Menu 

Background 

Lee and MacGregor (1985) conducted research in 

the area of menu depth and breadth. Their results led to 

a formula that would describe the optimal depth and 

breadth for a particular menu based on various process�

ing times. 

If reasonable processing and response times are put 

into the formula, the results lead to the recommenda�

tion to have between 4 and 13 items per panel (depend�

ing on the specific processing times). Their algorithm, 

however, ignores the option of organizing the data into 

27

categories within the panel. In addition, the effect of 

user’s experience on the organization of data was not 

included in the formula. 

Roske-Hofstrand and Paap (1986) extended the 

original work to include the effect of experience and 

the value of data categorization. 

General Description 

Experience with the same set of menu panels will 

shrink the scope of the search because the subjects 

now know the general location of their next item 

choice. In fact, “eye movement analysis showed that 

after 800 selections from the same menu the target 

was always found on the first fixation. With experi�

ence, menu users move from a state of great uncer�

tainty concerning the location of the target to one of 

near complete certainty” (Paap & Cooke, 1997). 

The optimal breadth is very sensitive to experience 

effects. As the users experience grows, the optimal 

breadth increases. For the condition in which no 

grouping is applied and in which the optimal breadth 

is found to be eight, this value grows to 38 as expertise 

is gained (Paap & Cooke, 1997). 

A similar reduction in the time to complete the 

search takes place when the options within an indi�

vidual panel are organized. Grouping is an extremely 

powerful influence in the depth-breadth trade-off. 

“For self-terminating search tasks, optimal menu 

sizes will usually be between 4 and 8 and may sometimes be as high as 13” (Paap & Cooke, 1997). In 

contrast, when meaningful groups of options can be 

presented for each menu, the “optimal breadth tends 

to be in the range of 16 to 36 and sometimes as high 

as 78” (Paap & Cooke, 1997; Figure 1). 

One way to think about the benefits of categoriza�

tion is that it accomplishes the same goal as funnel�

ing. Funneling refers to the reduction in the number 

of options that can be chosen to guide the user to the 

appropriate path. Categorizing the menu options 

within the panel enables the user to realize the ben�

efits of funneling, but without the response and 

execution time costs associated with greater depth. 

Guidelines 

• If meaningful groups of options can be presented for 

each menu, then the optimal breadth can increase 

from the 4 to 8 range, to the 16 to 36 range. 

• The more experienced the user is with the organiza�

tion, the greater the breadth should be. 

Constraints 

• The menus in these studies were homogenous (each 

panel had the same number of choices and each 

choice had the same depth below it). 

• “Reasonable” human response times (0.5 to 1 sec�

ond) were used. These laboratory times may be 

different than “reasonable” rates in the cockpit 

Key References 

Card, S., English, W., & Burr, B. (1978) Evaluation of 

mouse, rate-controlled isometric joystick, step 

keys, and text keys for text selection on a CRT. 

Ergonomics, 21, pp. 601-613. 

Francis, G. & Reardon, M. (1997). Aircraft Multifunc�

tion Display and Control Systems: A New Quan�

titative Human Factors Design Method for Orga�

nizing Functions and Display Contents. USAARL 

Report No. 97-18. U.S. Army Aeromedical Research Laboratory. Fort Rucker, Alabama. 

McDonald, J., Stone, J., & Liebelt, L. (1983) Searching 

for items in menus: The effects of organization 

and type of target. Proceedings of the Human 

Factors Society 27th Annual Meeting (pp. 834-

837). Santa Monica, CA: HFS. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., & Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Roske-Hofstrand, R. & Paap, K. (1986). Cognitive 

networks as a guide to menu organization: An 

application in the automated cockpit. Ergonomics, 29(11), pp. 1301-1311. 

Figure 1. Theoretical savings from grouping 

items. 

5 

10 

15 

20 

0 5 10 15 20 25 30 

breadth 

time (sec) 

no grouping 

grouping 

28

Organizational Aids for the Design of an MFD Menu 

Background 

It is important to properly categorize and organize 

the items in an MFD menu. In some cases, the 

categories are well known and distinct, and the intui�

tions of the designer match those of the users. However, in most cases the optimal organizational scheme 

is not obvious. Software engineers must overcome 

the temptation to generate their own organizations or 

to consult with only a single expert. 

If items are categorized according to the users’ 

perceived organization, users will locate items more 

quickly and with fewer errors. Menu organization 

also affects the formation of the users’ conceptual 

models of the system (McDonald, Stone, & Liebelt, 

1983). In cases where the user is a novice, the schema 

created by the more experienced and more typical 

users can help the novice develop a well-formed 

domain schema, thereby easing the transition from 

novice to system expert (Paap & Cooke, 1997). These 

advantages can not be realized when system designers 

generate their own organizational scheme. 

The practice of obtaining the users’ input to guide 

the design is one of the main principles of usercentered design. 

General Description 

There are many user-centered design success sto�

ries. Arguably, all design success is a result of apply�

ing, to varying degrees, the techniques, processes, 

methods, procedures, and philosophy that places the 

user at the center of the design process. 

Research on menu organization has indicated that 

“organizations generated from user data are superior 

to those based on designers’ intuitions” (Paap & 

Cooke, 1997). The menus based on user organization 

resulted in fewer errors, shorter selection times, and 

better recall, than the sortings of software designers. 

Research on MFDs also has shown similar advantages 

when the organization is ordered by groups of pilots, 

not designers or single experts in the field. It is 

insufficient to give the users category labels and have 

them assign the individual items to these pre-formed 

categories. In general, menus generated by multiple 

users outperform those generated by “experts” or the 

designers. 

Guidelines 

• Menu organizations should be based on data col�

lected from multiple users (pilots) who are represen�

tative of the target population. 

• The users should have complete freedom in determining the organization and should not be constrained by the designer’s preconceptions of categories. 

• The techniques, methods, and philosophy of the 

user-centered design process should be adhered to. 

(See ref. 4 for a description of the process). 

Constraints and Comments 

• Care needs to be given to insure that the users’ inputs 

are being provided and analyzed without any influ�

ence from the preconceptions of the designers. 

Key References 

Roske-Hofstrand, R. & Paap, K. (1986). Cognitive 

networks as a guide to menu organization: An 

application in the automated cockpit. Ergonomics, 29(11), pp. 1301-1311. 

Rubin, J. (1994). The problem of unusable products 

and systems. Handbook of Usability Testing. Wiley 

and Sons. pp. 3-23. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., & Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Seidler, K.S. & Wickens, C.D. (1992). Distance and 

Organization in Multifunction Displays. Human 

Factors, 34(5), pp. 555-569. 

Network Structures in an MFD Menu 

Background 

The majority of the menu organization research 

has concerned single-linked hierarchical issues. In 

particular, depth versus breadth issues. Compara�

tively little research has been conducted concerning 

alternate types of hierarchies. For instance, a network 

organization instead of a structured, single-linked 

hierarchy. 

“A network consists of a set of nodes and a set of 

links that connect the related nodes” (Paap & Cooke, 

1997). The important difference between the network and the traditional hierarchy is that each “node 

may have any number of incoming and outgoing 

links and the only requirement is that each node in a 

connected network must have at least one entry and 

one exit. One potential advantage with this kind of 

29

arrangement is that it can provide redundant pathways 

to the same menu panel” (Paap & Cooke, 1997). For 

many applications, a given panel naturally belongs to 

more than one general category – a case that the singlelinked hierarchy would not be able to satisfy. 

The goal of the designer of the MFD should be to 

create an organizational menu structure that is consis�

tent with the user’s cognitive model. A software tool 

known as Pathfinder has been designed to empirically 

obtain this conceptual user organization. 

Pathfinder (and other software tools) generate the 

family of link-weighted networks from any set of “dis�

tance” data. The distance data can be measures of 

functional similarity, physical similarity, co-occurrence, 

frequency of selection, or any other relationship (RoskeHofstrand & Paap, 1986, Seidler & Wickens,1992). 

General Description 

A cognitively guided network (i.e. one developed 

using tools such as Pathfinder) that offers the maxi�

mal number of meaningful pathways from the top 

level to the bottom level is easier to learn and use than 

the traditional hierarchical model (Roske-Hofstrand 

& Paap, 1986, Figure 1.). 

Guidelines 

• Menu organizations should be based on the pilots’ 

conceptual organization of the domain. 

• The input from the pilots should be used as the data 

for a Pathfinder type of tool that can be used to 

determine possible network organizations. 

Constraints and Comments 

• Consideration needs to be given to the difference 

between increased efficiency during the menu learn�

ing phase and during the longer operational phase. 

50 

60 

70 

80 

90 

100 

110 

120 

130 

1st test 2nd test 3rd test 4th test 

Figure 1. Mean trial time over tests for original 

menu, Pathfinder-designed, and a highly 

redundant Pathfinder menu (sec) 

mean trial ti

me (sec) 

orig. 

Path. 

high 

• Design decisions are still required concerning exactly 

which of the links should be included (i.e., how 

“strong” and “meaningful” is “strong and meaning�

ful” enough?). 

Key References


Roske-Hofstrand, R. & Paap, K. (1986). Cognitive


networks as a guide to menu organization: An 

application in the automated cockpit. Ergonomics, 29(11), pp. 1301-1311. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., and Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Adding Descriptors to the MFD Menu 

Background 

The total set of MFD options will likely be layered 

across multiple menu panels, thus requiring the user 

to navigate through the hierarchy to find the display 

of choice. 

The majority of errors in these menu-driven sys�

tems occur because the meaning of the options is not 

clear to the user. Users may make a particular selec�

tion only to later realize that they are heading down 

the wrong path. They will then have to back up and 

reselect a more appropriate path. This is both timeconsuming and frustrating to the pilots. 

One method of increasing the clarity of the menu 

choices is to append an expanded descriptor to each 

key word or phrase. Descriptors can include examples 

of items in the next layer down in the menu hierarchy. 

Presumably, the use of descriptors or key words will 

significantly reduce the number of dead ends that the 

pilot encounters. 

General Description 

The results of studies have clearly demonstrated 

that descriptors can be very effective when users have 

had limited experience with a menu panel. They are 

particularly helpful when the menu consists of op�

tions among general and abstract categories. Under 

these conditions, menus with descriptors result in 

fewer errors and are much preferred by users. 

The more abstract the categories, the more de�

scriptors are needed to provide the user with an 

understanding of the range of items contained in that 

category. Also, knowledge of the upcoming options 

was useful in making choices at the higher levels, but 

was not as helpful at the lower levels. 

30

Including a miscellaneous category into the menu 

choices creates a great deal of confusion and entices 

the navigators to the wrong path. This result is a good 

illustration of the power that context can play on the 

selection process. That is, the goodness of a name is 

very much determined by the other names appearing 

on the menu panel. Again, the importance of carefully choosing and organizing the hierarchy is seen. 

Guidelines 

• The options presented in an MFD menu display 

should include descriptors with them. 

• The more abstract, difficult, or infrequently used the 

options, the more descriptors are required. 

• The descriptors that are given should be examples of 

the next level down in the hierarchy, not middle level 

choices. 

• All things being equal (i.e. frequency of use and 

familiarity with), the further down the hierarchy, 

the less helpful the descriptors. Note that typically 

those choices further down are infrequently se�

lected and are therefore likely to require more 

descriptors, not less. 

• General “catch-all” choices such as miscellaneous 

should not be used. 

Constraints and Comments 

• There is a trade-off between the extra time required 

to scan the choices with descriptors, and the time cost 

associated with navigation errors. 

• Familiarity with the menu may lessen the value of 

descriptors relating to frequently used choices. 

Key References 

Dumais, S., & Landauer, T. (1983) using examples to 

describe categories. Proceedings of CHI ’83. pp. 

112-115. 

Lee, E., Whalen, T., McEwen, S., & Latremouille, S. 

(1984) Optimizing the design of menu pages for 

information retrieval. Ergonomics, 27, pp. 1051-

1069. 

Papp, K., and Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., & Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Snowberry, K., Parkinson, S., & Sisson, N. (1985) 

Effects of help fields on navigating through hier�

archical menu structures. International Journal of 

Man-Machine Studies, 22, pp. 479-491. 

Debunking the Icon Myth 

Background 

Many software applications have incorporated 

icons as aids in selection. These icons may be joined 

with the text descriptions, may be used in lieu of 

those descriptions, or may be an additional way to 

select the particular option. There are three possible 

advantages that icons may have over textual options. 

First, if icons replace words as target alternatives, 

then there are situations in which the display can be 

searched in parallel and there is a lowered cost asso�

ciated with having a large number of options on a 

single panel (Wolfe, 1994, cited in Paap & Cooke, 

1997). Second, categorization of pictures can sometimes be faster than words (Pellegrino, Rosinkski, 

Chiesi, & Siegel, 1977, cited in Paap & Cooke, 

1997). Third, “icons, like descriptions, can provide 

additional information that increases the accuracy of 

selections” (Paap & Cooke, 1997). 

General Description 

A tradeoff in the design of distinctive icons has 

been found. For instance, when the distinctiveness of 

an icon is enhanced by using simpler figures, it is 

likely that the simplification will make the icon more 

abstract and more error prone. On the other hand, 

more representational icons will be scanned sequen�

tially and slower - just like the words that they were 

designed to replace (Paap & Cooke, 1997). 

When icons are added to verbal labels, search 

times are improved. However, an equivalent im�

provement can also be realized by adding a verbal 

example. The results can be stated simply— supple�

menting category labels with icons is equivalent to 

adding a one-word example. 

Icons have very little value, as compared with 

verbal descriptors, when they are combined with 

verbal labels. For icons to be useful as stand-alone 

labels, they must have enough detail about both the 

“object and action to make them highly representa�

tional and easily understood” (Paap & Cooke, 1997). 

Often, these requirements will eliminate the icon’s 

visual distinctiveness (Paap & Cooke, 1997). 

Guidelines 

• Use verbal descriptors, not icons, to provide more 

information on a menu category. 

• In general, use icons sparingly. Their stand-alone value 

is difficult to realize, and their value combined with 

labels is no better than that of a verbal descriptor. 

31

Constraints and Comments 

• The presumed value of icons as space saving “shortcut” selections to frequently used tasks was not 

analyzed in these studies. 

Key References 

MacGregor, J. (1992) A comparison of the effects of 

icons and descriptors in videotext menu retrieval. 

International Journal of Man-Machine Studies, 37, 

pp. 767-777. 

Papp, K., & Cooke, N. (1997) Design of Menus in 

Helander, M., Landauer, T., & Prabhu, P. (eds), 

Handbook of Human-Computer Interaction. 

Elsevier Science Pub. pp. 533-572. 

Wolfe, J. (1994). Guided search 2.0: A revised model of 

visual search. Psychonomic bulletin and Review, 

1(2), pp. 202-238 

4.5 Automation 

Cockpit Automation 

Background 

“The modern airplane is the product of a program 

of research, development, and refinement in detail that 

no other structure or mechanism has ever matched. The 

results have been so remarkable that there is always 

danger of forgetting that these extraordinary craft still 

have to be operated by men, and that the most impor�

tant test they have to meet is still being operable without imposing unreasonable demands or unnecessary 

strains on the flight personnel.” 

—Edward Warner, 1946 

As in many other cases involving modern technol�

ogy, the question regarding automation is no longer 

“Can we do it?”, but “Should we do it?” 

The degree to which the modern aircraft has been 

automated is astounding. The newer aircraft “can 

operate almost unassisted from shortly after takeoff 

until they come to a rest after landing. Indeed, if all 

goes well, the human operator’s cognitive and psy�

chomotor skills are hardly called upon” (Billings, 

1997). 

Automation technology was originally developed 

with the hope of “increasing the precision and 

economy of operations while, at the same time, 

reducing operator workload and training require�

ments. It was considered possible to create a system 

that required very little or no operator intervention, 

and therefore reduced or eliminated the chance of 

human error within the system” (Sarter, Woods, & 

Billings, 1997). This original view of automation is 

based on the assumption that automating tasks that 

the human would ordinarily do would have no larger 

impact on the system in which that task occurred. In 

other words, the tasks that make up the larger system 

are essentially independent. “However, investiga�

tions into the impact of the introduction of automated technology into the cockpit have shown that 

this assumption is not correct. Tasks and activities 

are highly interdependent in actual, complex sys�

tems” (Sarter, Woods, & Billings, 1997). 

As a result of this interdependency, “only some of 

the benefits of automation have been realized” (Sarter, 

Woods, & Billings, 1997). “There has been a sharp 

decline in certain types of accidents that appear 

almost certainly to be due to the introduction of 

automation aids” (Billings, 1997). On the other 

hand, “several accidents and a large number of inci�

dents have been associated with and caused by the 

interaction between automation and the human op�

erators” (Billings, 1997). The general issues raised 

concerning automation in the cockpit also apply to 

the specific case of automating the display of infor�

mation on a multifunction display. 

Control automation “assists or supplants a human 

pilot in guiding an airplane through the maneuvers 

necessary for mission accomplishment” and has fol�

lowed “a generally evolutionary path” (Billings, 1997). 

Unlike the gradual advancements realized in control 

automation, information automation “has been 

marked by major changes due to the introduction of 

electronic display units (EDUs)” (Billings, 1997). 

The EDU capability “has made it possible to provide 

any sort of information in new and different formats” 

(Billings, 1997) and to modify and automate the 

presentation of that information in any way desired. 

Of particular relevance to MFDs, are the automa�

tion of aircraft subsystem displays. Although there is 

“still a philosophical controversy about the necessity 

of providing synoptic [summarized diagrammatic] 

subsystem information,” (Billings, 1997) many pilots find it desirable to have such displays in the 

cockpit. 

Automation issues become important when an 

anomaly occurs in a subsystem. Should a new subsystem display be brought up automatically or should 

the pilot have to do it? As the Douglas Chief of MD11 operations put it, “One of our fundamental strat�

egies has been, if you know what you want the pilot 

to do, don’t tell him, do it” (Hopkins, 1990). How32

ever, the strategy of automatically reconfiguring the 

displays can lead to a failure to present the “basic or 

root causes of the faults in the MD-11...and presents 

the potential for pilot confusion or surprises” (Bill�

ings, 1997). 

Control automation was brought into the cockpit 

with good intentions, but has resulted in mixed 

results. Similarly, information automation was intro�

duced to “alleviate pilot workload when dealing with 

anomalies” (Billings, 1997), but can instead increase 

the cognitive demand on the pilots. 

Numerous design issues arise from the original 

question of “Should we do it (implement the automa�

tion aid)?” The difficulty with creating automation 

rules that can be generalized into specific guidelines 

is similar to the difficulty with creating specific 

display guidelines that are applicable to all displays 

(see section 6). Each automation design choice has a 

unique set of pertinent issues and “questions.” It is 

difficult (if not impossible) to create a guideline that can 

be applied broadly across different design conditions. 

Specific guidelines exist and can only be created 

with an in-depth understanding of the design objec�

tives, the constraints, the conditions, the operating 

environment and the interrelations of these factors. 

As Billings (1997) put it, “I do not believe that 

specific “how-to” guidance is appropriate or particu�

larly useful except in the context of a particular 

system, within which there may be several, perhaps 

equally effective, ways to implement a particular 

function.” 

Many of the problems with automated systems are 

traceable to a “technology-centered” design process. 

A collection of specific guidelines will not alleviate 

the problems with automation. A change in the 

design process is the best way to counteract and 

prevent the difficulties. This new approach to the 

design process is a subset of the “human-centered 

design” discussed earlier, and is called “human-cen�

tered automation” (HCA) (Billings, 1997). 

There are many general guidelines or principles 

concerning automation that can aid the designer 

during the human-centered automation design ap�

proach. The following sections describe some of 

these principles, along with the nature of automation 

difficulties. 

Key References


Billings, C. (1997). Aviation Automation: The Search for


a Human-Centered Approach. Erlbaum Ass., Pub. 

New Jersey. 

Sarter, N., Woods, D., & Billings, C. (1997). Automa�

tion Surprises. In G.Salvendy (ed.) Handbook of 

Human Factors and Ergonomics. Wiley and Sons. 

pp. 1926-1943. 

Automation Problems: Feedback 

Background 

One problem with automation complexity is that 

the automation does not help the operators understanding of what is being controlled. “In earlier 

times, less capable automation simply controlled the 

airplane’s attitude and path; pilots could usually 

understand exactly what it was doing by observing 

the same instruments they used when they were 

controlling the aircraft manually” (Billings, 1997). 

Today’s automation is far too complex to accomplish 

this. “The information about what it is doing is 

almost always available somewhere in some form, 

although not necessarily in terms that the pilot can 

easily decipher. Why it is behaving a particular way 

and what it is going to do next is often not available 

except maybe in the requirement documents that 

motivated [the design]” (Billings, 1997). 

This problem is often referred to as the paradox of 

technology. Technology offers the potential to make 

things easier; to provide increased benefits. At the 

same time, added complexities arise to increase the 

user’s workload and frustration. As the product becomes more complicated, it becomes more important 

to provide proper feedback to the user (Norman, 

1990). Designers often purposely avoid presenting 

feedback of the automation process to keep the pilot 

from being overburdened with information that is 

not essential to the necessary functions (as understood by the designer). 

There is certainly a trade-off in the design decision 

regarding feedback. Opacity (lack of feedback) at 

some level is required so as not to overwhelm the 

pilot. It is important to consider that the ability of 

pilots to assimilate information is context depen�

dent. When more data is presented without adequate 

consideration of the context, it becomes less likely 

that pilots will attend to the most important data. 

With modern computers and graphics capabili�

ties, the designer now has the option to show what is 

really happening, to provide a good image that matches 

33

the person’s mental model of the task – thereby 

simplifying both understanding and performance. 

Three questions with which Wiener (1989) paraphrased the frequent responses of pilots to automa�

tion surprises were, “What is it doing?,” “Why is it 

doing that?,” and “What is it going to do next?” 

Providing adequate and context specific feedback to 

the pilot can help answer these questions. 

Key References


Billings, C. (1997). Aviation Automation: The Search for


a Human-Centered Approach. Erlbaum Ass., Pub. 

New Jersey. 

Norman, D. A. (1990). The design of everyday things. 

New York: Doubleday. 

Automation Problems: Complexity 

Background 

Current aircraft automation systems are capable, 

flexible, and very complex. When there is a problem, 

the pilot is expected to solve it. When the pilot 

perceives that automation has introduced an error, 

the pilot may not have a mental model of the system 

that enables proper diagnosis and corrective action. 

In this case, the pilot may revert to a lower level of 

management or may attempt to turn off the automa�

tion, which may unintentionally disable certain pro�

tective features (Curry, 1985). 

Mode errors are another problem arising from the 

flexibility of automation. Modern systems may have 

several modes for each of several control elements. 

General Description 

Norman (1990) explains that changing the rules 

often leads to errors. An example of changing the 

rules is a system that allows something be done one 

way in one mode and another way in another mode. 

Mode errors occur when a user executes an intention 

in a way appropriate for one mode when the system 

is in a different mode. Advanced systems are capable 

of changing modes (or modes within a mode) au�

tonomously. This capability for “indirect” mode 

changes without direct instructions from the pilot 

creates the potential for additional mode errors. Breakdowns in mode awareness are thought to have con�

tributed to a number of incidents and accidents 

(Sarter, Woods, & Billings, 1997). 

The flexibility of more advanced systems tempts 

automation designers to develop more complex and 

mode-rich systems. Not only has the number of 

modes increased, but also the complexity of their 

interactions (Sarter, Woods, & Billings, 1997). 

Guidelines 

• Minimize the number of modes in the automation. 

• Eliminate or limit the number of mode changes 

initiated by the software. 

• Ensure that if a procedure is done one way in one 

mode, it is done the same way in all modes. 

Key References 

Billings, C. (1997). Aviation Automation: The Search for 

a Human-Centered Approach. Erlbaum Ass., Pub. 

New Jersey. 

Curry, R. (1985). The introduction of new cockpit technology: A human factors study (NASA Tech. Mem. 

866659). Moffett Field, CA: NASA-Ames research Center. 

Norman, D. A. (1990). The design of everyday things. 

New York: Doubleday. 

Sarter, N., Woods, D., & Billings, C. (1997). Automa�

tion Surprises. In G.Salvendy (ed.) Handbook of 

Human Factors and Ergonomics. Wiley and Sons. 

pp. 1926-1943. 

Automation Problems: Workload 

Background 

The introduction of automation into the cockpit 

was expected to reduce crew workload. “It turned 

out, however, that automation does not have a uni�

form effect on workload” (Sarter, Woods, & Billings, 

1997). Many automated systems tend to support 

pilots during low-workload phases of flight but are of 

no use, or even act as a hindrance, when they are 

needed most – during time-critical dynamic situa�

tions (Sarter, Woods, & Billings, 1997). 

One reason for this dilemma is that automation 

does not have access to all the flight-relevant data. 

Therefore the crew must spend their time providing 

information to the automated system, deciding how 

automation should go about achieving the goal, and 

monitoring the automation closely to ensure that 

commands have been received and are being carried 

out as desired (Sarter, Woods, & Billings, 1997). 

“Workload is not only unevenly distributed over 

time, but it is sometimes unevenly distributed over 

the crew also” (Sarter, Woods, & Billings, 1997). For 

example, on many advanced flight decks the pilotnot-flying can be much busier than the pilot-flying 

because they are responsible for most of the interac34

tion with the automation interface (Sarter, Woods, 

& Billings, 1997). 

Key References 

Curry, R. (1985). The introduction of new cockpit technology: A human factors study (NASA Tech. Mem. 

866659). Moffett Field, CA: NASA-Ames research Center. 

Norman, D. A. (1990). The design of everyday things. 

New York: Doubleday. 

Sarter, N., and Woods, D. (1995) Strong, silent, and 

out-of-the-loop: Properties of advanced, cockpit automation and their impact on human-machine coordination (Tech. Rep. No. 95-TR-01). Cognitive 

Systems Engineering Lab., Ohio State Univ. 

Sarter, N., Woods, D., & Billings, C. (1997). Automa�

tion Surprises. In G.Salvendy (ed.) Handbook of 

Human Factors and Ergonomics. Wiley and Sons. 

pp. 1926-1943. 

Automation: Human-Centered Approach 

Background 

“There are disquieting signs in recent accident 

investigation reports that in some respects our 

applications of aircraft automation technology may have 

gone too far too quickly, without a full understanding 

of their likely effects on human operators” (Billings, 

1997). 

The concept of human-centered automation is an 

attempt to reevaluate the human-machine interac�

tions with the hopes of avoiding many of the automa�

tion problems that now confront pilots. “The thesis 

of this approach is that by beginning with the human 

and designing tools specifically to complement the 

human’s capabilities, we can build more effective and 

robust systems that will avoid or ameliorate many of 

the automation problems” (Billings, 1997). 

The following sections describe the principles of 

human-centered automation with some discussion 

on each. For a more thorough description, reference 

1 is recommended. 

Guidelines 

• The human operator must be in command. 

• Assist the pilot by providing an appropriate amount 

of feedback on the system. 

• Automation exists to assist pilots in carrying out 

responsibilities. Automation cannot deal with un�

certainty, does not have comprehensive knowledge 

of world states, and should not be in control. This 

means that the pilot’s responsibilities include detect�

ing shortcomings in the automation’s behavior, cor�

recting it when necessary, and continuing the 

operation. 

• The human operator must be involved in order to 

command effectively. To be involved is “to be drawn 

in.” The pilot must have an active role, whether the 

role is to control the aircraft directly, or to manage the 

machine resources through which control is being 

exercised. 

• Pilots should be required to complete meaningful 

tasks that have perceptual, cognitive and psychomo�

tor components so that pilots must perceive, detect, 

think about and respond actively to the stimulus. 

The goal of automation is not to alleviate the pilot of 

all the tasks. The pilot must be involved. 

• To remain involved, the human operator must be 

appropriately informed. Without appropriate infor�

mation concerning the operation, pilot involvement 

becomes less immediate and decisions become un�

predictable. 

• The human operator must be informed about automated systems behavior. It is necessary that pilots be 

aware both of the function (or malfunction) of the 

automated system and of the results of its processes, 

if they are to understand the behavior of the automated system. 

• Automated systems must be predictable. To know 

what automation to use, the pilot must be able to 

predict how the airplane will be affected by the 

particular automation, not only at the time that it is 

selected, but throughout the duration of the flight. It 

is also important that the pilot understand the full 

range of allowable behaviors of the automation aid. 

• Automated systems should monitor system faults 

and errors and should convey diagnostic and corrective information. Much effort has gone into making 

critical elements of the aviation system redundant. 

Because hardware, software, and humans all are 

capable of error, it is necessary that error detection, 

diagnosis, management, and correction be integral 

parts of automated systems (Wiener, 1993). 

• Each agent in an intelligent human-machine system must have knowledge of the intent of other 

agents. Cross-monitoring of machines by humans, 

of humans by machines, and of humans by hu�

mans can only be effective if the agent doing the 

monitoring understands what the monitored agent 

is trying to do. 

35

• Functions should be automated only if there is a 

good reason for doing so. If the time within which 

action is required following a signal or stimulus is less 

than will normally be required for detection, diagno�

sis, and decision to act, the task should be considered 

for automation. 

• If a task is very complex, requires many rote steps, or 

if the task is very difficult to perform correctly, the 

task should be redesigned or considered for automa�

tion. 

• If a complex task, improperly performed, will lead to 

a high probability of an adverse outcome, the task 

should be redesigned or, if this is not possible, 

considered for automation. 

• If a task is boring, repetitive, or distracting, especially 

if it must be performed frequently, that task should 

be considered for automation. 

• Automation should be designed to be simple to 

learn and to operate. 

• Automated systems must be comprehensible. As 

automation becomes more complex, it is likely to 

become more tightly coupled, with more potential 

interactions among modes. Pilots must be helped to 

understand the implication of these interactions. 

• Automation must insure that operators are not 

removed from the command role. Increasing inte�

gration and coupling of the ground and airborne 

elements of the Air Traffic Control system have the 

potential to bypass the pilots. One way to guard 

against this is to design future flight management 

systems so that the pilot is shown the consequences of 

any clearance before accepting it. 

• All automation elements and displays must enhance 

situation awareness. The minimum elements for 

situation awareness are a knowledge of the airplane’s 

position, velocity, attitude, error rate, status, threats, 

the status of the aircraft control automation and 

other aids, what must be done next, and when it must 

occur. 

• Automation must never be permitted to perform, or 

fail, silently. 

• Management automation should make human-machine systems easier to manage. A major problem 

with flight management systems is that they are 

cumbersome to operate. 

• Control automation must not be permitted to become “insubordinate.” Control automation should 

not be allowed to endanger an aircraft by causing an 

overspeed, a stall, or a contact with the ground. 

• Pilot authority to override normal operating limits 

should not be removed by the automation. Pilots 

may find it necessary to deliberately exceed safe 

operating limits to complete the mission with the 

highest degree of safety. 

• Aircraft control automation should be designed to 

be of most help during times of highest worn:kload. 

• Automation should be designed for maximum error 

resistance and maximum error tolerance. The sim�

plest possible architecture, clear, intuitive displays, 

and unambiguous responses to commands should be 

designed. 

• Emphasize information in accordance with its importance. The most important information should 

be most obvious and most centrally located. 

Key References 

Billings, C. (1997). Aviation Automation: The Search for 

a Human-Centered Approach. Erlbaum Ass., Pub. 

New Jersey. 

Norman, D. A. (1990). The design of everyday things. 

New York: Doubleday. 

Tenney, Y., Rogers, W. & Pew, R. (1995). Pilot Opinions on high Level Flight Deck Automation Issues: 

Toward the Development of a Design Philosophy. 

NASA Contractor Report 4669. Prepared for 

Langley Research Center. Contract NAS1-18788. 

4.6 Individual Displays: 

3D Versus 2D Displays 

Background 

As summarized by Wickens, Todd, and Seidler 

(1989), there are both benefits and costs associated 

with using a 3D (perspective) aviation display. One 

benefit is that a 3D visual scene is a more natural, 

“ecological,” or compatible representation of the 3D 

world than that provided by 2D displays. Another 

benefit is that a single integrated display of a 3D scene 

reduces the need for mental integration of multiple 

2D displays. 

“Conversely, a cost associated with using 3D dis�

plays is that any projection of a 3D world inevitably 

produces an inherent perceptual ambiguity” (Liu, 

1997). Depth is represented less accurately because 

the 3D display has to indicate distance in a nonlinear 

fashion. For any given 2D point within the display, 

there are an infinite number of potential 3D posi�

tions. Although a 3D display enables the user to 

achieve a holistic perception of the scene, it is more 

36

difficult to make accurate judgements on relations or 

values along any axis, particularly when one attempts 

to judge the distance between two points along the 

line of sight (Liu, 1997). Also, 3D displays are more 

susceptible to clutter (Garner, 1970). 

There is no shortage of studies examining the 

merits of 3D versus 2D displays in the aviation 

journals. There is however, a shortage of consistent 

and clear results illustrating the comparative benefits 

of the displays. 

Haskell and Wickens (1993) have introduced a 

concept known as the Proximity Compatibility Prin�

ciple (PCP) that has helped to explain the seemingly 

inconsistent results that the research has produced. 

The PCP predicts that “more integrated tasks will 

benefit from more integrated displays (the 3D dis�

play), whereas this benefit will be reduced, elimi�

nated, or even reversed for tasks requiring focusing 

attention” [on information from a single source] 

(Haskell & Wickens, 1993). Hence, there is a “com�

patibility” between proximity of information sources 

and do:egree of mental integration of these sources 

required by the task. The PCP predicts, for instance, 

that a 3D display will be superior for flight control 

(and for other integration tasks), but will be inferior 

for tasks that require precise readings along certain 

axis (e.g., vertical separation of aircraft, check read�

ing altitude) (Haskell & Wickens, 1993). With the 

PCP concept in mind, the following general descrip�

tions are excepted from selected research on the 

merits of 3D versus 2D displays for traffic, naviga�

tion, and weather displays. 

General Description 

Traffic Display: The information derived from 

traffic displays involves both types of requirements, 

integrated and focused, and therefore may not clearly 

be benefited by either a 3D or a 2D display. That is, 

there is a need to integrate the “parts” of the scene 

(which would presumably be aided by a 3D display), 

while the need to judge specific distances in a particu�

lar direction (aided by a 2D display) is also required. 

For a visual search and a tracking task performed 

using a traffic display, a 3D display enabled the pilots 

to perform better than with the 2D display. However, 

for a conflict detection task, subjects performed bet�

ter with the 2D coplanar display than the 3D display. 

Not only were more conflicts avoided, but the re�

sponse times were shorter (Figures 1,2). In addition, 

the pilots initiated more avoidance maneuvers in the 

wrong direction while using the 3D displays and 

subjective workload ratings also were lower for the 

2D coplanar display. 

Navigation Display: Currently, commercial aircraft displays exhibit primarily orthographic projec�

tions – “two dimensions without any information 

about the dimension not explicit in the display. 

When these displays do present information regard�

ing that dimension, they present it alphanumeri�

cally” (Haskell &Wickens, 1993). 

The demand on pilots to integrate data are already 

quite high, and the fact that the “dimension not 

explicit in the display” consists of alphanumerics can 

only increase the cognitive demands of integration. 

The inclusion of alphanumeric information requires 

the pilot to mentally transform and then integrate the 

data with the spatial information from the displays. 

The task of estimating the rate of change of these data 

points is also more difficult with the data in a 2D 

format. A 3D display would seem like a way to 

alleviate these problems because all three dimensions 

are presented spatially and a much more realistic 

80 

90 

100 

2D Coplanar 3D perspective 

Figure 1. Conflict detection rate for 

different displays. 

Conflict detection rate (

%) 

10 

15 

20 

2D Coplanar 3D perspective 

Figure 2. Mean response times for 

conflict trials (correct detections 

only). 

Response time for c

onflicts 

37

picture of the environment is produced. Indeed, for 

a three-dimensional, spatial, dynamic task (e.g., lat�

eral and altitude control), a 3D display is preferable 

(Figure 3). While for tasks that require attention to 

be focused on a single axis (airspeed control), a 2D 

display is superior. Again, these results are consistent 

with the PCP. 

Weather Display: According to the Federal Avia�

tion Administration (as cited in Wickens, Campbell, 

Liang, & Merwin, 1995) weather is cited as a cause of 

40 percent of aircraft accidents and 65 percent of air 

traffic delays. One reason the weather is so dangerous 

is the traditional lack of accurate and timely informa�

tion provided to the pilots. 

Presently, pilots and controllers rely on raw radar 

returns, surface or pilot observations, and their own 

experience to interpret weather patterns and make 

operational decisions. A recent study (Phillips, 1993, 

as cited in Boyer & Wickens, 1994) has shown that 

the present system has limitations in both safety and 

effectiveness. On one hand, underestimating a weather 

situation can put aircraft and passengers at risk un�

necessarily. On the other hand, error on the side of 

safety, such as avoiding marginal weather all to�

gether, can result in time delays and wasted fuel and 

airspace in the terminal area. 

With the latest generation of supercomputers, 

newly installed weather observing systems, high speed 

data communications, and modern computer-gener�

ated graphics, it is now possible to present weather 

forecast information in a format that meets user’s 

needs (U.S. GAO, 1993). The integration and pre�

sentation of the weather data raises the question of 

which type of display should be used – 3D or 2D. 

It might seem that a 3D rendering would be the 

natural choice to display weather data. After all, 

weather is a 3D phenomenon and the information in 

all three axis must be integrated in order to compre�

hend fully the weather constraints. 

Nevertheless, research results did not show evi�

dence that pilots perform better with the 3D display. 

In fact, the statistically significant results showed 

that the 2D displays enabled superior performance 

(Figure 4, 5). Also, in an informal debrief, the pilots 

preferred the 2D view. 

Guidelines 

Traffic Display:

• There have been some encouraging studies regarding 

3D displays utilizing depth cues (ref. 6,9). However, 

the existing data do not support the recommendation 

of a 3D display for traffic information. 

• A coplanar 2D display is recommended for the 

display of traffic information. 

Figure 3. Flight path tracking accuracy for 

control w ith 2D and 3D displays. 

0 

1 

2 

3 

4 

5 

Lateral Altitude Airspeed 

Dimension 

LN (RMS error) 

2D 

3D 

86 

90 

94 

98 

102 

106 

2D 3D 

Figure 4. Time to complete trial for each 

display. 

Trial tim

e (sec) 

0.5 

0.55 

0.6 

0.65 

0.7 

2D 3D 

Figure 5. Percent of situation 

aw areness questions answ ered 

correctly by pilots. 

Correct r

esponses (

%) 

38

Navigation Display:

• Consider including a 3D ADI that incorporates 

command path boxes and an aircraft predictor. 

Weather Display:

• 2D displays are recommended for the display of 

weather information. 

• A planar view simultaneously displayed with a profile 

view is recommended for the display of weather 

information. 

Constraints 

Traffic Display:

• The 2D display must be a coplanar display. The 

single 2D display leads to poorer performance than 

the coplanar display. 

• The 3D perspective display did not have depth cues 

(ref. 2,4,7) 

Navigation Display:

• The display used in the experiment (ref 2) was a 

hybrid of the Attitude Director Indicator (ADI) and 

the navigation display. 

• Widely varying navigational screens were used (ref 1, 

5). 

• Only landing approaches were flown (ref 5). 

Weather Display:

• Student pilots were used (ref. 8). 

• The sole task was to navigate around a weather 

problem (ref. 3). 

• Subjects simulated ATC with the task of vectoring an 

aircraft around a weather formation (ref. 8). 

Key References 

Andre, A., Wickens, C., Moorman, L., & Boschelli, M. 

(1991). Display Formatting Techniques for Im�

proving Situation Awareness in the Aircraft Cockpit. The International Journal of Aviation Psychology, 1(3), pp. 205-218. 

Bemis, S., Leeds, J. & Winer, E. (1988). Operator 

Performance as a Function of Type of Display: 

Conventional versus Perspective. Human Factors, 

30(2), pp. 163-169. 

Boyer, B. & Wickens, C. (1994). 3D Weather Displays 

for Aircraft Cockpits. ARL-94-AA/NASA-94-4. 

NASA Ames Research Center. Moffett Field, CA. 

Ellis, S., McGreevy, M., & Hitchcock, R. (1987). 

Perspective Traffic Display Format and Airline 

Pilot Traffic Avoidance. Human Factors, 29(4), 

pp. 371-382. 

Haskell, I. & Wickens, C. (1993). Two- and ThreeDimensional Displays for Aviation: A Theoreti�

cal and Empirical Comparison. The International 

Journal of Aviation Psychology, 3(2), pp. 87-109. 

Mazur, K. & Reising, J. (1990). The Relative Effective�

ness of Three Visual Depth Cues in a Dynamic 

Air Situation Display. In Proceedings of the Human Factors Society 34th Annual Meeting, pp. 16-

20. Santa Monica, CA: HFS. 

Merwin, D. &Wickens, C. (1996). Evaluation of Perspective and Coplanar Cockpit Displays of Traffic 

Information to Support Hazard Awareness in Free 

Flight. Technical Report ARL-96-5/NASA-96-1. 

Aviation Research Laboratory. Institute of Avia�

tion. University of Illinois at Urbana-Champaign. 

Wickens, C., Campbell, M., Liang, C. & Merwin, D. 

(1995). Weather Displays for Air Traffic Control: 

The Effect of 3D Perspective. ARL-95-1/FAA-95-

1. University of Illinois at Urbana-Champaign 

Technical Report. Aviation Research Laboratory. 

Zenyuh, C., Reising, J., Walchli, S. & Biera, D. (1988). 

A Comparison of a Stereographic 3-D Display 

versus a 2-D Display. In Proceedings of the Human 

Factors Society 32nd Annual Meeting, pp. 53-57. 

Santa Monica, CA: HFS. 

Component Arrangement

Background 

Cockpit display components must be arranged 

within some physical space. “Ideally, each compo�

nent would be placed in such a way as to optimize the 

ability of that component to serve its purpose. This 

optimum location would be predicted from [task 

requirements], human capabilities and characteris�

tics, and would facilitate performance of the activi�

ties carried out in that space” (Sanders & McCormick, 

1993). 

Unfortunately, it is usually not possible to place 

each component in its optimum location. Tradeoffs 

are required. 

These design tradeoffs concern not only the physi�

cal layout of the various displays, but also the ar�

rangement of the information and menu choices 

within a multi-function display (MFD). 

39

Sanders and McCormick (1993) describe four 

principles that can be used to help aid the designer. 

1) Importance Principle: This principle states that im�

portant components be placed in convenient loca�

tions. Importance refers to the degree to which the 

component is vital to the achievement of the system 

objectives. The determination of importance usu�

ally is a matter of judgement made by experts (i.e. 

users) in the system operation. 

2) Frequency-of-Use Principle: This principle states that 

frequently used components be placed in conve�

nient locations. 

3) Functional Principle: This principle provides for the 

grouping of components according to their func�

tion, such as the grouping of displays that are 

functionally related in the operation of the system. 

4) Sequence-of-use principle: In the use of certain sys�

tems, sequences or patterns of relationship frequently 

occur in the operation of tasks. In applying this 

principle, the items would be arranged to take advantage of such patterns. 

General Description 

In putting together the various components of a 

system, no single principle can, or should, be applied 

consistently across all situations. 

The notions of “importance” and “frequency” are 

particularly applicable to the basic phase of locating 

components in a general area. The “sequence-of-use” 

and “functional” principles tend to apply more to the 

arrangement of components within a general area 

(Sanders, McCormick, 1993). 

One study found that, if the operational require�

ments actually do involve the use of the components 

in consistent sequences, then the “sequence-of-use 

principle” should be followed (Figure 1). 

Guidelines 

The four design principles described above should be 

applied to the design of MFD menus, but only on the 

basis of rational judgement, following the humancentered design philosophy. There is little empirical 

evidence that specifically supports these design prin�

ciples. 

If the operational requirements are such that the com�

ponents or selections are used in a consistent se�

quence, then the sequence-of-use principle is 

recommended. 

Figure 1. Time required to carry out tasks (in 

rather consistent sequences) with displays 

arranged on the basis of four principles. 

5 

10 

15 

20 

Frequency Importance Functional Sequence 

of use 

Time (sec) 

Constraints 

• There has not been a significant amount of research 

in this area. 

• The experimental task used in the research may not 

adequately emulate cockpit tasks. 

• The test subjects were students, not pilots. (ref 1). 

Key References 

1. Fowler, R., Williams, W., Fowler, K., and Young, D. 

(1968). An investigation of the relationship between 

operator performance and operator panel layout for 

continuous tasks (Tech. Rept. 68-170). U.S. Air 

Force AMRL (AD-692 126). Wright-Patterson 

Air Force Base, OH. 

2. Kochhar, D. and Barash, D. (1987). Status displays 

in automated assembly. Applied Ergonomics, 18(2), 

pp. 115-124. 

3. Sanders, M., and McCormick, E. (1993). Human 

Factors in Engineering and Design. McGraw-Hill 

Inc. 456-482. 

4. Sargent, T.A., Kay, M.G., and Sargent, R.G. (1997). 

A Methodology for optimally Designing Console 

Panels for Use by a Single Operator. Human 

Factors, 39(3), 389-409. 

Screen Layout

Background 

An important design issue for MFDs is the simul�

taneous but separate presentation of displays. It may 

be desirable to allow more than one display to be 

presented simultaneously. That is, when the pilot 

40

selects a new display, it does not take the place of the 

current display but may go into a quadrant of the 

screen, allowing up to four displays to be shown at 

once. In addition to the partitioning of the display, 

there is also the concern of how to organize the fields 

within a display. 

General Description 

Boff and Lincoln (1988) have compiled a collec�

tion of guidelines to aid in screen layout and structur�

ing that can also be applied to the design of MFDs. 

Guidelines 

• The user should be permitted to divide the screen 

into windows of appropriate size. 

• Dashed lines may be used to segment the display. 

• The unused areas should be used to separate logical 

groups, rather than having all the unused area on one 

side of the display. 

• In data entry and retrieval tasks, the screen should be 

functionally partitioned into different areas to dis�

criminate among different classes of information for 

commands, status messages, and input fields. 

• To enhance important or infrequent messages or 

alarms, they should be placed in the central field of 

vision relative to the display window. 

• The organization of displayed fields should be stan�

dardized. Functional areas should remain in the same 

relative location on all frames. This permits the users 

to develop spatial expectancies. 

• Data should be arranged in logical groups: sequen�

tially, functionally, by importance or by frequency. 

• Logically related data should be clearly grouped and 

separated from other categories of data. 

• Data should be arranged on the screen so that the 

observation of similarities, diffe ̃rences, trends, and 

relationships is facilitated for the most common uses. 

• In computer-initiated dialogues, each display page 

should have a title that indicates the purpose of the 

page. 

• In data entry and retrieval tasks, the last four lines 

on each display page should be reserved for mes�

sages, to indicate errors, communication links, or 

system status. 

• Only required information should be displayed to 

avoid information overload or display clutter. The 

additional information should be available upon 

request. 

Constraints 

• These guidelines were not generated specifically for 

MFDs. 

• These guidelines may be based accepted practices 

rather than empirically validated research. 

Key References


Boff, K. & Lincoln, J. (1988). Screen Layout and


Structuring in Person-Computer Displays. In 

Engineering Data Compendium: Human Perception and Performance, Section 11.332. AAMRL, 

Wright-Patterson AFB, OH. 

Brown, C., Burkleo, H. Mangelsdorf, J., Olsen, R., & 

Williams, A., Jr. (1981). Human factors engineering criteria for information processing systems. Sunnyvale, CA. Lockheed. 

Williges, B. & Williges, R. (1984). Dialogue design 

considerations for interactive computer systems. 

In F. Muckler (Ed.) Human factors review: 1984. 

Santa Monica, CA: Human Factors Society. 

Pictorial Displays

Background 

Technological advances have enabled designers to 

present information in the form of color pictures and 

schematics that can be rapidly changed and updated 

under software control. This capability may allow for 

the integration into one display of information dis�

tributed across several instrument readings and doz�

ens of abstract symbols with alphanumeric codes 

(Stokes, Wickens, & Kite, 1990). 

“Pictures and pictorial schematics can condense 

information into readily recognized ‘Gestalts’ in which 

the interrelationships between the data become much 

clearer” (Stokes, Wickens, & Kite, 1990). The pic�

ture is able to display the data in a way that is 

compatible with the pilot’s mental model of the 

system. 

The incorporation of pictorial displays also fol�

lows the display principle of pictorial realism. “The 

objective of which is to make the static representation 

of aviation displays conform as much as possible to 

the real-world configuration of the displayed item” 

(Stokes, Wickens, & Kite, 1990). 

Many of the modern glass cockpits provide synop�

tic or summarizing diagrams of the various aircraft 

subsystems. With the increased power and speed of 

the on-board computers, it is expected that the num�

ber of schematics that the pilot can choose via the 

MFD will grow rapidly. 

41

General Description 

There is evidence that a redundant combination of 

pictorial and verbal information leads to a better 

understanding than either text or illustration on its 

own. Pictorial schematics that are unfamiliar and 

have no explanatory text are no more effective than 

text alone. 

In general, pilots favor color pictorial formats – 

except when presented in a head-up display. Perfor�

mance has been found to be better with the color 

displays. 

Research also has revealed that the color pictorial 

is most effective when the display presentation is of 

short duration, or if the task was either complex or 

required that the pilot mentally recall an earlier 

screen (Stokes, Wickens, & Kite, 1990). 

Guidelines 

• Pictorial displays should be used whenever possible 

for the presentation of subsystem data. 

Constraints 

• It is somewhat unclear exactly what portion of the 

benefits of color pictorial displays result from the use 

of color. 

•� Some studies did not find any advantage with the 

pictorial displays. The merits of presenting spe�

cific information in a pictorial format should be 

considered. 

Key References 

Hawkins, J., Reising, J., & Gilmour, J. (1983). Picto�

rial format display evaluation. In Proceedings of 

the National Aerospace and Electronics Conference 

1983, pp. 1132-1138. New York: IEEE. 

Stokes, A., Wickens, C., & Kite, K. (1990). Display 

Technology Human Factors Concepts. University of 

Illinois Aviation Research Lab. SAE, Inc. 

Stollings, M. (1984). Information processing load of 

graphic versus alphanumeric weapon format displays for advanced fighter cockpits. U.S. Air Force 

Flight Dynamics Lab, Wright-Patterson Air Force 

Base, OH. Tech report AFWAL-TR-84-3037. 

Design of Icons and Symbols

Background 

The designer of display icons or symbols must 

ensure that the icons convey the intended informa�

tion in combination with other related symbols that 

may appear. 

As flight decks become more information inten�

sive, the difficulty of properly designing the icons 

increases. As Pejtersen and Rasmussen (1997) put it, 

“The possibilities concerning the design of icons are 

enormous and there are no rules or guidelines for 

making the best (or avoiding the worst) selection.” 

Like other issues in display design, specific guidelines will not lead the designer to an optimal solution. 

Success comes from a combination of general guidelines and a structured design approach early in the 

development cycle. 

General Description 

The SAE Committee G-10 has produced an aero�

space standard titled “Human Interface Design Meth�

odology for Integrated Display Symbology” (see ref 

1). The document outlines a recommended approach 

for the design of integrated display symbology in 

support of flight tasks. 

Guidelines 

• Common symbology should be avoided for tasks 

that require different responses. The likelihood of 

operator error in this situation increases dramati�

cally, especially if the task elicits a skill-based behav�

ior. Even when appropriate training has been provided, 

high stress situations are often characterized by op�

erator reversion to previously learned, and now incorrect, behavior. 

• The designer must establish clearly that the informa�

tion encoding of any standard symbology is both 

necessary and sufficient to support the intended task. 

• Where the importance of the information warrants, 

the information should be encoded using two or 

more symbol attributes (e.g., color, size, and shape). 

• Care must be taken to ensure that symbol attributes 

that have strong attention getting value (e.g., flashing 

color) are used sparingly and only when justified by 

the relative priority of the top-level task in relation to 

all of the user’s other tasks. 

To ensure compatibility with a wide range of end-user 

individual differences, multiple test subjects should 

be used to evaluate the symbology. 

Constraints and Comments 

• When applying this design process, consideration 

should be given to the more “general” user-centered 

design approach (ref 3). 

42

Key References 

Aerospace Recommended Practice. (1988). Human 

Interface Design Methodology for Integrated Display 

Symbology. ARP 4155. Society of Automotive 

Engineers, Inc. 

Pejtersen, A., & Rasmussen, J. (1997). Ecological Information Systems and Support of Learning: Cou�

pling Work Domain Information to User Char�

acteristics. In Helander, M., Landauer, T., & 

Prabhu, P. (eds.) (1997). Handbook of HumanComputer Interaction. Elsevier Sciences. pp. 315-

346. 

Rubin, J. (1994). The problem of unusable products 

and systems. In Handbook of Usability Testing. 

Wiley and Sons, Inc. pp. 3-46. 

Icons: Complexity and Concreteness

Background 

“The visual metaphor lies at the heart of modern 

graphical user interfaces. The benefits ascribed to its 

use rest largely on the belief that pictorially realistic 

icons allow users to apply pre-existing world knowl�

edge to the display domain” (Curry, McDougall, & 

de Bruijn, 1998). These metaphors aim to capitalize 

on correspondences that exist between real world 

objects and representations of those objects. 

The term “concreteness” refers to the “degree of 

pictorial resemblance that an icon has to its realworld counterpart” (Curry, McDougall, & de Bruijn, 

1998). “When icon concreteness is high, parallels 

with the real world enable users to form expectations 

that can guide their use of the system” (Curry, 

McDougall, & de Bruijn, 1998). The drive towards 

using visually realistic icons can be counter-produc�

tive if it increases the level of visual complexity. 

Design guidelines mention that icons should be 

kept as simple as possible (Easterby and Zwaga, 

1984). Does an icon have to be complex in order to 

be concrete? 

General Description 

Complexity of icons can be accurately measured 

by adding the number of horizontal, vertical and 

diagonal lines, arcs, arrowheads, letters and special 

characters they contain (Garcia, Badre & Stasko, 

1994). Complexity is not necessarily related to con�

creteness. A visual metaphor can be conveyed without having to add complexity. 

Concreteness significantly affected accuracy and 

response times, while complexity had no effect. An 

icon does not have to be complex to be concrete. 

Guidelines 

• Icons should be kept as simple as possible and as 

concrete as possible. The visual metaphor makes the 

icons effective; complexity by itself adds nothing. 

Constraints 

• The benefits of the visual metaphor may fade for 

icons in regular use. 

• Complexity may have to be added to obtain the 

desired concreteness. 

Key References 

1. Curry, M., McDougall, S. & De Bruijn, O. (1998). 

The Effects of the Visual Metaphor in Determin�

ing Icon Efficacy. In Proceedings of the Human 

Factors Society 42nd Annual Meeting, pp. 1590-

1594. Santa Monica, CA: HFS. 

Figure 1. Accuracy rates for icon 

characteristics. 

40 

50 

60 

70 

80 

90 

Concrete Abstract 

Accuracy rate (%) 

Simple 

Complex 

Figure 2. Response times for icon 

characteristics. 

2 

2.25 

2.5 

2.75 

3 

Concrete Abstract 

Response time (sec) 

Simple 

Complex 

43

2. Easterby, R. & Zwaga, H. (1984). Information design: The design and evaluation of signs and printed 

material. Cichester: Wiley and Sons Ltd. 

3. Garcia, M., Badre, A., & Stasko, J. (1994). Develop�

ment and validation of icons varying in their 

abstractness. Interacting with Computers, 6, pp. 

191-211. 

4.7 General Design Principles for Aircraft 

Displays 

The Principle of Pursuit Tracking

Background 

“In many aircraft steering displays, the pilot’s task 

is to track and null a computed steering error indica�

tion” (Roscoe, 1968). Such a task is not only required 

in both air-to-air and air-to-surface weapon delivery 

for military aircraft, but also in flying ILS landing 

approaches for commercial aircraft (Roscoe, 1968). 

In most cases, “the displayed indications tell the 

pilot nothing about what their aircraft is doing or 

what the target is doing, but merely the differences 

between the two” (Roscoe, 1968). If these differences 

are nulled, the aircraft will be on the desired flight 

path. These displays typically present the error indi�

cations by means of a single moving element (i.e. a 

pair of cross-pointer indices that show the horizontal 

and vertical components of the error). These types of 

displays are known as compensatory tracking dis�

plays (Roscoe, 1968). 

These compensatory displays could be modified in 

such a way, however, so that the target and the 

representation of the ownship both move indepen�

dently against a common coordinate system. These 

types of displays are known as pursuit displays because the pilot’s task is to cause the ownship symbol 

Figure 1. Comparison of pursuit and 

compensatory displays. 

0 

0.2 

0.4 

0.6 

0.8 

1 

1-5 6-10 11-15 16-20 21-25 26-30 

Trials 

Average steering error 

(degrees) 

Compensatory Display 

Pursuit Display 

to pursue the independently moving target symbol 

(Roscoe, 1968). 

At present, the majority of pursuit displays are 

found in military applications, advances in technol�

ogy may quickly change that. Global Positioning 

System technology has the potential to revolutionize 

aircraft landing procedures. It will enable pilots to fly 

complex, curved approaches rather than the more 

simple straight-in approaches necessitated by ILS. 

Navigational aids are being designed to assist the 

pilot’s with this task. Examples include pathway and 

tuc:nnel displays incorporated into either a modern�

ized Primary Flight Display (PFD) or into a separate 

display. Important human factors design issues are 

associated with how to present the desired flight path 

to the pilot. 

General Description 

Considerable experimental evidence indicates that 

tracking performance is significantly improved with 

the use of pursuit displays. Studies comparing the 

steering errors found with compensatory and pursuit 

have found approximately a two-to-one difference 

favoring the pursuit display. Discussions elsewhere 

in this report have indicated the advantage of por�

traying ownship as the moving part (e.g. the principle 

of the moving part and the frequency-separated atti�

tude display). This principle is extended here. Perfor�

mance is improved when the goal of desired 

performance (e.g., target symbol or command indi�

cation) also moves independently against the same 

external reference system (Roscoe, 1968). 

Guidelines 

• Pursuit rather than compensatory displays are rec�

ommended for tracking tasks. That is, the pilot’s 

aircraft and the target symbol or command indica�

tion should both move independently against the 

same reference system. 

Constraints 

• Modern pathway or tunnel displays were not tested 

in these studies. 

Key References


Bauerschmidt, D., & Roscoe, S. (1960) A comparative


evaluation of a pursuit moving-airplane steering 

display. IRE Trans. Human Factors in Electronics, 

HFE-1(2), pp. 62-66 

44

Roscoe, S. (1968). Airborne Displays for Flight and 

Navigation. Human Factors, 10(4), 321-332. 

Roscoe, S. (1980). Controls and Displays in Aviation 

Psychology. Iowa State Univ. Press, pp. 33-124. 

The Principle of the Moving Part

Background 

The question of whether the part of the display 

that represents the aircraft should move against a 

fixed scale or whether the coordinate system should 

move against a fixed index representing the aircraft, 

has long been a controversial subject in display design 

(Roscoe, 1968). As more information is available 

from multiple sources, and as the space within the 

displays becomes a more valuable commodity, it 

becomes more tempting to incorporate a moving 

scale with a fixed index of the aircraft, thus saving 

space that would be used to display the entire scale. 

This design decision manifests itself in many sepa�

rate issues. For example, as Roscoe (1968) describes: 

1) Heading – should the compass rotate against a fixed 

line so that heading can always be read at the top of 

the display, or should a pointer rotate relative to a 

fixed compass so that the display movement is clockwise when the aircraft is turning right and vice versa? 

2) Altitude – should altitude be represented by one or 

more pointers moving against a fixed altitude scale or 

should a moving scale be read against a fixed line 

index? 

3) Attitude – should the horizon bar move against a 

fixed aircraft symbol or should the aircraft symbol 

move against a fixed outside world? 

General Description 

“There is an impressive body of experimental and 

operational evidence that the part of the display that 

represents the aircraft should move rather than the 

scale” (Roscoe, 1968). The results are so consistent 

that Roscoe (1968) has described this as a design 

principle (i.e. “the principle of the moving part”). 

:The simple explanation as to why the aircraft 

should move and not the scale or environment is that 

when pilots move the controls of their aircraft, they 

expect the aircraft and the aircraft symbol to not only 

move, but to move in the same direction as the 

control movement. The pilot “intuitively” expects 

the display to function this way. 

Another advantage with the fixed scale is that the 

pilot can “immediately get a good deal of approxi�

mate information from looking at the display without reading the scale numbers. This is particularly 

important if the information is required for a quick 

check reading” (Roscoe, 1968) or if it needs to be 

integrated with other information that maybe stored 

in short term memory. 

Although this research is old and much of it was 

conducted with “uni-functional” displays, the results 

are relevant to the design of modern cockpits. Today’s 

designers are less constrained by technology and do 

not have to present the entire scale or compass or 

airspeed dial. They now have the tempting option of 

presenting only the current value of the indicator, 

which can easily lead them into designing a poorer 

interface. 

Guidelines 

• Adherence to the “principle of the moving part” is 

recommended. Specifically, whichever part of the 

display represents the aircraft should be the moving 

part as opposed to the scales or environment. 

Constraints 

• For cases when the exact “quantity” is required of the 

display, either a digital readout of the values can be 

added or a moving scale with clearer gradations may 

be needed. 

Key References 

1. Christensen, J. (1955). The importance of certain dial 

design variables in quantitative instrument reading. 

USAF: WADC TR pp. 55-376. 

2. Roscoe, S. (1968). Airborne Displays for Flight and 

Navigation. Human Factors, 10(4), pp. 321-332. 

3. Roscoe, S. (1980). Controls and Displays in Aviation 

Psychology. Iowa State Univ. Press, pp. 33-124. 

Proximity Compatibility Principle

Background 

“Indicators or displays in an aircraft are rarely 

presented in isolation. The sheer number of indica�

tors can lead to clutter, increased information access 

cost, and in extreme situations, information overload” (Wickens & Carswell, 1997). To understand 

how the operator deals with this wealth of informa�

tion, we must consider how we routinely combine 

sensory elements to form the higher-order entities we 

call groups. This concerns the problem of perceptual 

organization. 

45

The “Proximity Compatibility Principle” deals 

specifically with the issue of display organization 

(Barnett & Wickens, 1988). In general, the principle 

holds that those “indicators or displayed data values 

that are conceptually related or that need to be used 

in combination should belong to the same perceptual 

group. In short, related information should be per�

ceptually proximate” (Wickens & Carswell, 1997). 

In order to group similar displays, similarity must 

be defined. This display “relatedness” or similarity is 

composed of task, correlational, system, and integra�

tion relatedness. Wickens and Carswell (1997) fur�

ther describe these types of similarity as follows: 

1) Task relatedness: Degree to which information in two 

displays must be used together to complete a task. 

2) Correlational relatedness: Degree to which changes in 

the information in two displays are correlated over 

time. 

3) System relatedness: Similarity of the systems underly�

ing the two displays. 

4) Integrated Relatedness: This measure is similar to task 

proximity, but involves displays of information that 

the user must integrate. 

General Description 

When the task requires a large amount of integra�

tion, performance decreases as the distance of the 

data to be integrated is increased (Figure 1). The 

distance described here is not necessarily a physical 

(or metric) distance, but a psychological or percep�

tual distance. The psychological distance can be 

manipulated. For example, the needed items can be 

enclosed in a box. 

Figure 1. Perceptually proximate data 

presentation as a function of the integration 

required within the task. 

50 

55 

60 

65 

70 

75 

80 

85 

90 

95 

None Low High 

Task integration level required 

Correct answers (%) 

Perceptually Near 

Perceptually Far 

Guidelines 

• In general, displays or items that are related (per the 

four types of relatedness) should be grouped to�

gether. 

• In general, displays or items that must be integrated, 

should be grouped together. 

Constraints 

• The research providing the basis for these guidelines 

was not conducted in an aviation setting. 

• Tradeoffs must be considered between “relatedness” 

and other principles such as frequency-of-use and 

sequence-of-use. 

Key References 

1. Barnett, B. & Wickens, C. (1988). Display Proxim�

ity in Multicue Information Integration: The 

Benefits of Boxes. Human Factors, 30(1), pp. 15-

24. 

2. Vincow, M. & Wickens, C. (1992). Space and the 

Proximity-Compatibility Principle: Traditional and 

Computational Models Approaches to Displayed 

Information. ARL-92-7/ NASA A3I-92-2. Uni�

versity of Illinois at Urbana-Champaign Techni�

cal Report. Aviation Research Laboratory. 

3. Wickens, C. & Carswell, C. (1997). Information 

Processing. In G. Salvendy, Ed., Handbook of 

Human Factors and Ergonomics. New York: Wiley 

and Sons, Inc. pp. 89-129. 

Emergent Features

Background 

“Emergent features are relational properties of a 

group of display elements that are not properties of 

any of the elements in isolation” (Pomerantz, 1981). 

“These emergent features are often rapidly detected 

by the user. For example, a series of vertical, movingpointer displays that are placed side by side may 

produce the emergent feature of pointer alignment” 

(Wickens & Carswell, 1997). In this way, the detec�

tion of the emergent feature provides a shortcut to the 

reading of each individual pointer and the effortful 

task of checking each value. Note that if the indica�

tors were “not exactly the same in scale design, had 

different baselines, or were located at distant parts of 

the display panel, then alignment would not be 

available to use as a cue” (Wickens & Carswell, 

1997). 

Another way to create emergent features is through 

the creation of object displays. “Object displays in46

clude any arrangement of elements that make the 

different data values appear to be part of a single 

perceptual object” (Wickens & Carswell, 1997). For 

instance, lines or contours can be added directly 

between data-varying dimensions (i.e. line graphs). 

Multiple indicators can be arranged so that the addi�

tion of line segments creates a closed object (Beringer, 

Howard, & Jenkins, 1986, Wickens & Carswell, 

1997). 

Examples of object displays include polygon-polar 

diagrams, box displays, and other multidimensional 

object displays. A row of parallel bar graphs, clustered 

ordering of different colors, or 3D contours for 

example, can all create emergent features and facili�

tate information integration tasks (Wickens & 

Carswell, 1997). 

Designing with emergent features in mind is an 

example of how the designer can capitalize on a 

human perceptual characteristic. Visual processing 

of attributes of a single object is parallel and obliga�

tory. It is parallel because people pay attention to all 

the dimensions or attributes at once. It is obligatory 

because people have no control over the process – one 

cannot notice one dimension or attribute of an object 

but ignore the others (Wickens & Carswell, 1997). 

General Description 

It is not an easy task to represent variables as 

emergent features that highlight the critical data 

relationships (Bennett et al, 1993). Decisions must 

be made concerning which variables should be in�

cluded in the graphic form, how they should be 

assigned dimensions, whether they should be con�

verted to common scale, and how to represent the 

task context. In addition, the application of emergent 

features requires a detailed understanding of the tasks 

for which the display will be used. 

Studies have found that as the task becomes more 

integrated, the value of salient emergent features 

increases (Figure 1). Similarly, if the task remains a 

focused task in which individual data points are not 

integrated, the application of emergent features is of 

less use (Figure 2). 

Guidelines 

• If data values must be integrated, or are related 

functionally or conceptually, then emergent features 

should be exploited if possible. 

Figure 1. Errors for different tasks 

using different display designs 

(configural display has more salient 

emergent features). 

2 

3 

4 

5 

6 

Integrated task Focused task 

Error magnitude (

%) 

Configural display 

Separable display 

Figure 2. Completion time for different 

tasks using different display designs 

(configural display has more salient 

emergent features). 

2 

2.5 

3 

3.5 

4 

Integrated task Focused task 

Task time (sec) 

Configural display 

Separable display 

Constraints and Comments 

• Because the application of emergent features is taskdependent and display-dependent, it is not always 

feasible. 

Key References 

Bennett, K., Toms, M., & Woods, D. (1993). Emer�

gent Features and Graphical Elements: Designing 

More Effective Configural Displays. Human Factors, 35(1), pp. 71-97. 

Beringer, D., Howard, F. & Jenkins, J. (1986). Putting 

Information in the Visual Periphery: It beats a 

Pointed Stick in the Eye. In Proceedings of the 

Human Factors Society 30th Annual Meeting, pp. 

613-617. Santa Monica, CA: HFS. 

47

Pomerantz, J. (1981). Perceptual organization in infor�

mation processing. In M. Kubovy & J.R. 

Pomerantz, Eds., Perceptual Organization pp. 141-

180. Hillsdale, NJ: Erlbaum. 

Wickens, C. & Carswell, C. (1997). Information Pro�

cessing. In G. Salvendy, Ed., Handbook of Human 

Factors and Ergonomics. New York: Wiley and 

Sons, Inc 

Command and Status Displays 

Background 

Stimulus-response (S-R) compatibility has long 

been a “theme in the psychological literature since it 

was introduced by A.M. Small in a 1951 paper 

presented to the Ergonomics Research Society” (Andre 

& Wickens, 1992). “The concept was later popular�

ized by Fitts and Seeger (1953) who showed that 

responses to corresponding stimulus and response 

sets was faster relative to less ‘natural’ arrangements” 

(Andre & Wickens, 1992). 

The distinction between command and status dis�

plays can also be described in terms of S-R compat�

ibility. For instance, a command display tells the 

operator what to do, and if the language of its com�

mand is motion, then it is S-R compatible (i.e. an 

upward display movement triggers an upward con�

trol movement). “The intention of this type of dis�

play is to negate the need to cognitively interpret the 

operational meaning of the display movement (‘Am 

I too high? Too low?’)” (Andre & Wickens, 1992). 

“Some command displays, like the flight director 

of a modern aircraft for instance, provide the operator with direct advice regarding the direction of 

control” (Andre & Wickens, 1992). This format, 

however, bypasses a representation of the state for 

which the command is required. In effect, the com�

mand display “tells the pilot what to do without 

displaying the reasons why” (Andre & Wickens 1992). 

On the other hand, “the status display provides the 

‘why’ information, telling the operator what exists” 

(Andre & Wickens, 1992). The status display requires a corrective movement that is S-R incompat�

ible (i.e. an upward display movement triggers a 

downward control movement). This type of display 

is similar to a compensatory tracking task and im�

poses an extra transformation (Simon, 1969). 

The issue for cockpit display design is when to use 

command displays and when to use status displays. 

General Description 

Applied research findings reveal that status dis�

plays increase the accuracy of comprehending system 

states and, presumably, lead to a greater situational 

awareness (Figure 1). Consistency was found to be 

more important than whether the “appropriate” type 

of display was used (i.e. status or command) 

Guidelines 

• To promote situational awareness, individual dis�

plays should be “status” displays vice “command” 

displays. 

• It is important to have consistency between the 

individual displays. If a command display is to be 

introduced, the form of it must be distinctly different 

from the status display so that there is little opportu�

nity for confusion (e.g. the “climb, climb, climb” 

auditory warning on the TCAS). 

Constraints 

• There has not been a significant amount of research 

in this area. 

• A relatively simple flight control task was used in this 

research. 

• Vocal tasks as well as control tasks were analyzed. 

Some of the advantages with the status display were 

found to a larger extent with the vocal tasks. 

Key References 

1. Andre, A.D. & Wickens, C.D. (1992). Compatibil�

ity and Consistency in Display-Control Systems: 

Implications for Aircraft Decision Aid Design. 

Human Factors, 34(6), pp. 639-653. 

2. Fitts, P., & Seeger, C. (1953). S-R compatibility: 

Spatial characteristics of stimulus and response 

codes. Journal of Experimental Psychology, 46, pp. 

199-210. 

3. Simon, S. (1969). Reactions toward the source of 

stimulation. Journal of Experimental Psychology, 

81, pp. 174-176. 

Displaying Uncertainty 

Background 

Few studies have addressed the issue of displaying 

the uncertainty of information presented in displays 

(Andre & Cutler, 1998). Rapid advancements in 

commercial avionics, integrated navigation tracking 

systems, and data link communications lead to an 

increased importance of information uncertainty 

(Andre & Cutler, 1998). 

48

There are “proposed and expected changes to the 

structure of the National Airspace System that de�

pend on the data presented to the pilots” (Andre & 

Cutler, 1998). “Free Flight” proposes an air space 

system whereby pilots have the authority to determine their own air routes without air traffic control�

ler intervention” (Andre & Cutler, 1998). This 

concept depends on advanced situation awareness 

displays that can provide detailed information on 

other aircraft. 

The uncertainty about the accuracy or reliability 

of the data presented to the pilots can lead to situa�

tion awareness problems. “As the pilot experiences 

both false alarms and misses due to both the existence 

and lack of representation of the data uncertainty, 

they may develop a lack of trust in, and eventual 

decrease in use of, the automated system” (Parasur�

aman & Riley, 1997, cited in Andre & Cutler, 1998). 

Since there will be a mixed avionics equipage fleet 

for some time to come, there will be an issue of how 

to combine information with different levels of accu�

racy and timeliness on an integrated display (Johnson, 

1998). 

General Description 

Little work has been done to evaluate and compare 

various techniques for displaying uncertainty. In 

addition to this, the issues of displaying the uncer�

tainty of informational aspects other than aircraft 

position appear to be unexplored. 

In navigation tasks, it was found that without 

uncertainty symbology, each increase in uncertainty 

was accompanied by an increase in the frequency of 

collisions and near misses. Thus, without a constant 

spatial reminder of the uncertainty, subjects either 

ignore or forget about it. Also, the graphical-explicit 

(ring around the icon) symbology was found to be 

superior to the text or graphical-implicit (color) sym�

bology for displaying uncertainty (Andre & Cutler, 

1998). 

Guidelines 

• When data uncertainty can affect safety, an indica�

tion of the level of data uncertainty should be dis�

played. 

Constraints and Comments 

• To date, there are not enough research studies to 

support any design recommendations for displaying 

uncertainty. 

Key References 

1. Amar, M., Vaneck, T., Chaudhry, A., & Hannon, 

D. (1995). A preliminary evaluation of electronic 

taxi charts with GPS derived position for airport 

surface situational awareness. Proceedings of the 8th 

International Symposium on Aviation Psychology, 

pp. 499-504. 

2. Andre, A., & Cutler, H. (1998). displaying uncer�

tainty in advanced navigation systems. In Proceedings of the Human Factors and Ergonomics 

Society 42nd Annual Meeting. pp. 31-35. Santa 

Monica, CA: HFES. 

3. Johnson, W. (1998). Issues and concerns in the 

design of cockpit displays of traffic information. 

In Proceedings of the Human Factors and Ergonomics Society 42nd Annual Meeting. 40-41. Santa 

Monica, CA: HFES. 

4. Parasuraman, R. & Riley, V. (1997). Humans and 

automation: Use, misuse, disuse, abuse. Human 

Factors, 39, pp. 230-253. 

5.0 SAMPLES FROM EXISTING 

GUIDELINES OR STANDARDS 

Boff and Lincoln (1988) Engineering Data


Compendium


Abstract


The Boff and Lincoln (1988) compendium is a 

series of tools aimed at providing the data necessary 

for the human engineering design of crew systems. 

The compendium provides in-depth treatment of 

human perception and performance in terms of the 

variables that influence the human operator’s ability 

to acquire and process information, and make effec�

tive decisions. 

General Description 

The three-volume compendium is an excellent 

source of information on a wide variety of human 

factors issues. A large section is dedicated to display 

interfaces. The following guidelines were based on 

information given in the display interfaces section of 

Boff and Lincoln (1988). 

Sample Guidelines 

Guidelines for Designing Alerting Signals. 

1) Present high-priority alerting signals both visually 

and aurally. Maximize the probability of detection 

of each mode of the warning signal. 

49

2) The detectability of high-priority visual alerting 

signals should be maximized as follows: 

a) Present visual alerting signals as close to the 

operator’s line of sight as possible— maximum 

deviation of 15° for high priority alerts and 30° for 

lower priority. 

b) Visual alerting signals should subtend at least 1° 

of visual angle. 

c) Visual alerting signals should be twice as bright as 

other visual displays on the instrument panel. 

d) A visual alerting signal should be flashing against 

a steady background. 

3) The detectability of auditory alerting signals should 

be maximized as follows: 

a) Auditory alerts should be multiple frequency 

with more than one frequency in the range of 250 to 

4000 Hz. 

b) The amplitude of an auditory signal should be at 

least 15 dB above the amplitude of the masked 

threshold. 

c) An auditory alerting signal should be intermittent 

or changing over time. 

Voice and Tone Warning Signals. 

1) Voice warning signals should be incorporated for the 

situations in which reaction time is very important. 

2) If multiple auditory alarms and a corresponding 

checklist are planned, consideration should be given 

to implementing a voice auditory warning system 

instead. 

3) Making a verbal warning longer by including more 

words in the semantic condition does not improve 

response times; a keyword warning should be used. 

Guidelines for the Use of Noncritical Auditory 

Signals. 

1) An auditory signal should be used to alert and direct 

the user’s attention to the appropriate visual display. 

2)� The optimum type of signal should be carefully 

evaluated, so that it is readily noticed by the user but 

not startling or interfering with others in the imme�

diate area. Because of variable background noises, 

the intensity should be adjustable. 

3)� The intensity, duration, and source location of 

the signal should be compatible with the acousti�

cal environment of the intended receiver as well 

as with the requirements of other personnel in the 

signal area. 

4) Auditory signals should be intermittent, allowing 

the user sufficient time to respond. The signal should 

be automatically shut off by user response action. 

5)� Auditory signals should be triggered by system 

failures. 

6)� Non-critical auditory signals should be capable of 

being turned off at the discretion of the user. 

Alarm Classification and Development. 

1) Lessen the amount of alerts. Pilots report that there 

should be no more than four auditory alerts, and 

one preferred. 

2)� Alerts should be prioritized and each alert should 

carry information about how critical it is. 

3) Non-critical alerts should not occur during periods 

of high workload; they should be delayed. 

4) Alarms should be classified into categories in terms 

of their importance so that an appropriate warning 

system can be designed. The following classification 

is recommended: 

a) Warning – Requiring immediate attention and 

mandatory immediate response. 

b) Caution – Requiring immediate attention and 

rapid response. 

c) Advisory – Requiring general awareness of a 

marginal condition. 

Clay (1993) DOT-FAA-93-18 

Abstract 

This report provides guidelines for the application 

of cognitive issues to the design of electronic instru�

ment approach procedure (EIAP) displays. It pre�

sents 46 cognitive issues and 108 design principles. 

Its basic premise is that pilots need to be given 

unambiguous information as quickly and easily as 

possible in such a way that it can be understood and 

remembered until the time that it must be used. 

Recognition and discriminability of patterns, stress 

resulting from heavy workload, the effects of divided 

attention, and the need to take account of the pilot’s 

expectations are discussed. The merits of color and 

size, paper and electronic display, and temporary 

removal of nonessential information are examined. 

General Description 

Key cognitive issues are described along with many 

guidelines to EIAP design. Sections include topics 

such as Perception and Cognition, Attention and 

Performance Limitations, Organization and Group�

ing of Information, and Dynamic Displays. Many of 

50

the guidelines are appropriate beyond EIAPs to MFD 

design generally. 

Sample Guidelines 

Perception and Cognition. 

1) Eliminate any irrelevant information from the dis�

play. 

2) Use redundant coding of targets (make targets differ�

ent on more than one dimension – shape, size, color). 

3) Make object features distinctive. 

4) If a moving map is used, display symbols with an 

upright (track-up) orientation at all times. 

Attention and Performance Limitations. 

1) Locate frequently sampled information centrally. 

2) Information items that are often sampled sequen�

tially should be located close together. 

3) Avoid presenting information in such a way that 

inappropriate information is more salient than ap�

propriate information. Motion, color, highlighting, 

and size may make information more salient. 

Organization and grouping of Information 

1) Use task analyses to determine groupings of infor�

mation that are meaningful for the task. 

2) Minimize the number of codes that are used for 

grouping. 

Dynamic Displays 

1) Provide decluttering techniques that do not remove 

information completely. 

2) A cue to what information is on hidden screens 

should be present at all times. 

Department of Defense (1991) MIL-STD-411E 

Abstract 

The purpose of this standard is to establish uni�

form requirements and provide functional design 

criteria for an effective aircrew station alerting sys�

tem. The use of new technology is encouraged where 

it can be demonstrated that the use of the technology 

will result in shorter aircrew response times and more 

effective aircrew action subsequent to presentation of 

the alert. 

General Description 

This standard gives descriptions of the require�

ments for alerting systems within aircraft. 

Sample Guidelines 

• Warning signals. Advisory signals. The use of advi�

sory signals in the cockpit area shall be minimized to 

avoid unnecessary distraction of the aircrew and to 

minimize factors that compromise the night vision 

capability of the crew. 

• Integrated alert displays. Number and location of 

displays. The number of displays shall be based upon 

the informational requirements of the aircrew and 

the reliability of the displays. All warning, caution 

and advisory messages shall be presented within the 

operator’s 30-degree forward cone of vision, on a 

single display surface, insofar as practical. If more 

than one display is present at a crew station, the 

display farthest to the left should display all warning, 

caution, and advisory messages. 

• Message format. Color coding. When color is used 

to provide a unique and easily distinguishable coding 

method for all three alerting categories, red shall be 

reserved for warning messages, yellow shall be reserved for caution messages, and a third color (green 

preferred with blue and white as non-flightdeck 

options) shall be used to represent advisory level 

messages. 

• Audio warning signals. Wheels-up signal. When a 

nonverbal audio wheels-up signal is used, it shall have 

the following tone. 

a) Frequency = 250 ± 50 Hz. 

b) Fundamental tone interrupted at 5 ± 1 Hz. 

c) 50 ± 10 percent on-off cycle. 

Department of Defense (1984) MIL-STD-783D 

Abstract 

This standard establishes the requirements for 

legends to be used for marking controls and displays 

in aircrew stations and on airborne equipment. 

General Description 

This standard gives recommended abbreviations 

(legends) for a large collection of terms that may be 

used in an aircrew station. 

51

Sample Guidelines 

Department of Defense (1984) MIL-STD-1295A 

Abstract 

The purpose of this standard is to establish human 

factors design criteria for symbolic and alphanumeric 

information used on electronically and optically gen�

erated airborne displays. Electronically and optically 

generated displays are those in which an image is 

presented to the observer directly on the imagegenerating surface or indirectly through an optical 

projection system. The symbolic presentation pro�

vides flight, combat, and cargo-handling informa�

tion with or without video imagery for rotary-wing 

aircraft. This standard is restricted to those display 

devices used in aircraft for the purpose of flight or 

mission control. Separate radar or electronic warfare 

displays are not included. 

Word Legend

Absolute 

Acceleration (Gravity) 

Acquire 

Accumulator 

Actuate 

Adjust 

Advantage 

Afterburner 

Aileron 

Aircraft 

Airspeed 

Alternate 

Alternator 

Altitude 

Ambient 

Ampere 

Amplifier 

Antenna 

Armament 

ABS 

G 

ACQ 

ACC 

ACTU 

ADJ 

ADV 

A/B 

AIL 

ACFT 

A/S 

ALTN 

ALTNR 

ALT 

AMB 

AMP 

AMPL 

AMPTD 

ANT 

General Description 

This document describes the general requirements 

for the information presentation of airborne elec�

tronic display elements. Although it is specifically for 

helicopters, much of the information and guidelines 

are applicable to aircraft displays in general. 

Sample Guidelines 

1) Information presentation characteristics. 

2) Information presented by the displays shall be in 

symbolic, pictorial, or alphanumeric forms as speci�

fied by the procuring activity. 

3)� The meaning and motion of symbols shall be con�

sistent throughout all modes of the display. Scaling 

and gain changes are permitted between modes. 

4)� The sense of aircraft control symbol motion should 

be compatible with the motions of the correspond�

ing controller. 

Head-up/helmet-mounted displays. 

The HUD/HMD shall present all essential flight 

and mission information. All information reflected 

from the display shall be collimated and or sufficient 

brightness to be seen in a real-world background of 

10,000 foot-candles illumination. 

Department of Defense (1989) MIL-STD-1472D 

Abstract 

This standard establishes general human engineer�

ing criteria for design and development of military 

systems, equipment and facilities. Its purpose is to 

present human engineering design criteria, principles 

and practices to be applied in the design of systems, 

equipment and facilities to support the following 

objectives: 

a) Achieve required performance by operator, control 

and maintenance personnel. 

b) Minimize skill and personnel requirements and train�

ing time. 

c) Achieve required reliability of personnel-equipment 

combinations. 

d) Foster design standardization within and among 

systems. 

General Description 

This document provides requirements and recom�

mendations concerning the design of a wide variety 

of military systems and equipment. In addition to 

52

sections on displays, there are sections on controls, 

labeling, anthropometry, and hazards and safety, to 

name a few. 

Sample Guidelines 

Visual Displays. Information. 

Content. The information displayed to an operator 

shall be sufficient to allow the operator to perform the 

intended mission, but shall be limited to that which 

is necessary to perform specific actions or to make 

decisions. 

Precision. Information shall be displayed only 

within the limits and precision required for specific 

operator actions or decisions. 

Redundancy. Redundancy in the display of infor�

mation to a single operator shall be avoided unless it 

is required to achieve specific reliability. 

Audio Displays. Audio warnings. 

Audio signals shall be provided, as necessary, to 

warn personnel of impending danger, to alert an 

operator to a critical change in system or equipment 

status, and to remind the operator of a critical action 

or actions that must be taken. 

Touch-screen controls for displays. 

Touch-screen control may be used to provide an 

overlaying control function to a data display device 

such as CRTs, dot matrix/segmented displays, elec�

troluminescent displays, programmable indicators, 

or other display devices where direct visual reference 

access and optimum direct control access are desired. 

Department of Defense (1996) MIL-STD-1472E 

Abstract 

This standard establishes general human engineer�

ing criteria for design and development of Military 

systems, equipment and facilities. Its purpose it to 

present human engineering design criteria, principles 

and practices to be applied in the design of systems, 

equipment and facilities so as to: a) Achieve required 

performance by operator, control and maintenance 

personnel. b) Minimize skill and personnel require�

ments and training time. c) Achieve required reliabil�

ity of personnel-equipment combinations. d) Foster 

design standardization within and among systems. 

General Description 

This design standard includes specifications and 

guidelines for a wide range of systems and subsystems. 

A sample of the section titles reveals such varied topics 

as control/display integration, light-emitting diodes, 

design of labels, and anthropometry. 

The section on visual display is concerned more 

with physical dimensions of displays, rather than 

design guidelines, and are of limited help within the 

scope of this project. The proper illumination, reflec�

tion, and lines of sight are typical concerns that are 

addressed in this section. 

Sample Guidelines 

• Visual displays. Display illumination. Normal. 

When maximum dark adaptation is not required, 

low brightness white light shall be used; however, 

when maximum dark adaptation is required, low 

luminance (.07-.35 cd/m2) red light (greater than 

620 nm) shall be provided. 

• Visual displays. Information. Content. Information 

displayed to an operator shall be sufficient to allow 

the operator to perform the intended mission, but 

shall be limited to information necessary to perform 

specific actions or to make decisions. 

• Visual displays. Location and arrangement. Vibration. Vibration of visual displays shall not degrade 

user performance below the level required for mis�

sion accomplishment. 

Workspace design. Seating. Cushioning and upholstery. Where applicable, both the backrest and seat 

shall be cushioned with at least 25 mm of compress�

ible material and provided with a smooth surface. 

Upholstery shall be durable, nonslip, and porous. 

Department of Defense (1996) MIL-STD-1787B 

Abstract 

This standard describes symbols, symbol formats, 

and information content for electro-optical displays 

that provide aircrew members with information for 

takeoff, navigation, terrain following/terrain avoid�

ance, weapon delivery, and landing. It describes sym�

bol geometry, font, recommended dimensions, and 

mechanizations. This document also defines the sym�

bology requirements for a primary flight reference 

and describes some fundamental relationships between symbol motion and aircraft system states. 

53

General Description 

This document gives the graphical requirements 

for the collection of symbols that appear on aircraft 

displays. The requirements are very specific for the 

individual symbols, describing the angles, dimen�

sions, and thickness of all the symbology. 

Sample Guidelines 

Bearing pointer. The bearing pointer displays the 

relative bearing to the selected navaid station. The 

pointer shall be located 20 mm from the center of the 

bearing indicator and shall be free to rotate a full 360 

degrees about the center. If the navaid is not receiving 

a signal from a station, then the pointer shall not 

display. 

6 mm 

10 mm 5mm 

3 mm 

Department of Defense (1989) MIL-HDBK-761A 

Abstract 

The purpose of this handbook is to provide guidance 

in the application of human engineering to the design 

and development of management information software 

systems. The users of this document are intended to be 

any individual, or group, who participates in the devel�

opment of software systems, including logicians, software engineers, end-system users, software development 

managers, programmers, system evaluators, and human 

factors engineers. 

General Description 

The first portion of this document contains a de�

scription of a recommended design process, a general 

approach to rapid prototyping, and a collection of 

human factors engineering design principles. The ma�

jority of the document contains detailed guidelines 

concerning the design of “systems that perform routine 

processing functions, but which are designed so that 

processing will produce information that will assist in 

decision making.” Sample topic areas include labeling 

and terminology, data entry feedback, speech input, 

data display, flowcharts, and error feedback. 

Sample Guidelines 

Graphics. Maps and situation displays. Format 

1) Orientation of maps and situation displays should 

be consistent or under user control. 

2)� When maps present large geographic areas, a consis�

tent method of projecting the earth’s curvature on a 

flat display surface should be specified and adopted. 

3) Distance judgements from map displays should be 

supported through grid overlays, pointing devices, 

or other means. 

Expert Systems. Graphic interface. 

1)� The expert system should have the capability to 

graphically represent its rules network. This capa�

bility should be available to the user as an adjunct to 

the explanation subsystem. 

2)� Graphics, such as a system schematic, should be 

used to depict relationships between system configuration and measurable parameters. 

3) Graphics should portray system/ component/pro�

cess status through the use of color, shading, or 

similar coding techniques. 

4) Coding techniques should be consistently applied 

across the expert system. 

Speech Output. 

1)� Computer-generated speech output may be used for 

guidance messages in environments with low ambi�

ent noise, when a users attention may not be di�

rected toward a visual display, or when providing a 

visual display is impractical. 

2)� Computer-generated speech messages should be lim�

ited in number, distinctive from routine messages, 

short and simple. 

Data Display. Display control. 

1) Users should be able to tailor information displays 

by controlling data; selection coverage, updating, 

and suppression, and should be able to specify data 

for display. An easy means to return to normal 

display coverage should be provided. 

2)� Users should be able to control displayed data or 

enter new data when required by the task. 

54 
3) As required, users should be able to print paper 

copies of information displayed. 

4)� Users should not be required to remember data 

accurately from one display page to another. 

Federal Aviation Administration (1994) 

AC 20-130A 

Abstract 

This advisory circular (AC) establishes acceptable 

means, but not the only means, of obtaining airworthi�

ness approval of multi-sensor navigation or flight man�

agement systems integrating data from multiple 

navigation sensors for use as a navigation system for 

oceanic and remote, domestic en route, terminal, and 

non-precision instrument approach operations. This 

document does not address GPS equipment incorporat�

ing differential GPS capability. Like all advisory material, this advisory circular is not, in itself, mandatory and 

does not constitute a regulation. It is issued for guidance 

purposes and to outline one method of compliance with 

airworthiness requirements. 

General Description 

Much of the information in this circular concerns 

installation and evaluation of the navigation equip�

ment. There is however, one section concerning the 2D 

accuracy requirements of the GPS sensor. These re�

quirements are similar to those found in RTCA Docu�

ment No. RTCA/DO-208, “Minimum Operational 

Performance Standards for Airborne Supplemental 

Navigation Equipment Using Global Positioning Sys�

tems (GPS).” (Listed later in section.) 

Sample Guidelines


System Accuracy. 2D Accuracy Requirements (95


percent probability)


For equipment incorporating a Class B( ) or C( ) 

GPS sensor, the total position fixing error of the 

airborne multi-sensor equipment shall be equal to or 

less than that shown in the following table when GPS 

data is used in the position/navigation computation: 

Oceanic & remote (nm) 

position 

fixing 

CDI 

centering 

.124 .20 

en route (domestic) (nm) .124 .20 

Terminal (nm) .124 .20 

non-precision approach 

(nm) .056 .01 

Federal Aviation Administration (1987) AC 25-11 

Abstract 

This advisory circular (AC) provides guidance for 

certification of cathode ray tube (CRT) based electronic 

display systems used for guidance, control, or decisionmaking by the pilots of transport category airplanes. 

Like all advisory material, this document is not, in itself, 

mandatory and does not constitute a regulation. It is 

issued to provide guidance and to outline a method of 

compliance with the rules. 

General Description 

The material provided in this AC consists of guid�

ance related to pilot displays and specifications for 

CRT’s in the cockpit of commercial airplanes. The 

contents include sections on information separation, 

display visual characteristics, and information display, 

for example. Although the majority of the guidance 

concerns individual displays, there are some guidelines 

that can be useful for the design of a MFD. 

Sample Guidelines 

Information Display. Full-Time vs. Part-Time Displays. Some aircraft parameters or status indications are 

required by the FAR to be displayed, yet they may only 

be necessary or required in certain phases of flight. If it 

is desired to inhibit some parameters from full-time 

display, an equivalent level of safety to full-time display 

must be demonstrated. Criteria considered include the 

following: 

1) Continuous display of the parameter is not required 

for safety of flight in all normal flight phases. 

2)� The parameter is automatically displayed in flight 

phases where it is required. 

3) The inhibited parameter is automatically displayed 

when its value indicates an abnormal condition, or 

when the parameter reaches an abnormal value. 

4) Display of the inhibited parameter can be manually 

selected by the crew without interfering with the 

display of other required information. 

5)� If the parameter fails to be displayed when required, 

the failure effect and compounding effects must 

meet requirements. 

6)� The automatic, or requested, display of the inhib�

ited parameter should not create unacceptable clut�

ter on the display; simultaneous multiple “pop-ups” 

must be considered. 

7) If the presence of the new parameter is not suffi�

ciently self-evident, suitable alerting must accom�

pany the automatic presentation. 

55

Information Separation. Color Standardization 

1)� The following depicts acceptable display colors re�

lated to their functional meaning recommended for 

electronic display systems. 

2) Specified display features should be allocated colors 

from one of the following 

3) �Precipitation and turbulence areas should be coded 

as follows: 

Federal Aviation Administration (1996) 

Abstract 

Advances in technology have enabled increasingly 

sophisticated automation to be introduced into the 

flight decks of modern airplanes. Generally, this 

automation was added to accomplish worthy objec�

tives such as reducing flightcrew workload, adding 

additional capability, or increasing fuel economy. 

Item Color 

Warnings Red 

Flight envelope, 

system limits 

Red 

Cautions, abnormal 

sources 

Amber 

Earth Tan/Brown 

Scales /assoc. figures White 

Engaged modes Green 

Sky Cyan/Blue 

ILS deviation pointer Magenta 

Flight director bar Mag./Green 

Vulnerabilities do exist, though, and further safety 

improvements should be made. As a result, the Federal 

Aviation Administration chartered a human factors 

team to address problems in design, training, flight crew 

qualifications, and operations, and to recommend ap�

propriate means to address these problems. 

General Description 

This document is an excellent source for descriptions 

of usability problems that have been experienced in the 

modern cockpit and, to a lesser extent, a source for 

design recommendations. The various sections include 

Flightcrew Management, Situation Awareness, and 

Design Processes. 

Much of the document describes the problems that 

need to be solved, and generally what needs to be done 

(e.g. The FAA should assure that analyses are conducted 

to better understand why flightcrews deviate from pro�

cedures). There is a lack, however, of specific design 

recommendations. Nevertheless, this document is a 

good source of general guidelines, which can be valuable 

in the design process. 

Sample Guidelines


Automation Management. FMS design.


1)� Critical or irrevocable entries should be confirmed 

before they are executed, as well as providing an 

“undo” capability when appropriate. 

2) There is a need for standardization of route, leg, and 

constraint conventions such as waypoint entry con�

ventions, definition, and implementation of verti�

cal profiles in order to reduce error potential and 

facilitate easier transitioning between airplane types. 

Automation Management. Flightcrew information. 

1) The flightcrew should be provided with the 

manufacturer’s higher-level design philosophy (e.g., 

the reasons for automating particular functions) to 

the extent that this philosophy could affect opera�

tional use. 

2)� The flightcrew should be provided with a descrip�

tion of the envelope of protection features, includ�

ing specific capabilities and limitations, and the 

situations or flight conditions for which envelope 

protection is or is not available. 

Color Sets: Set#1 Set#2 

Fixed ref. 

symbols 

White Yellow 

Current data White Green 

Armed modes White Cyan 

Selected data Green Cyan 

Selected 

heading 

Magenta Cyan 

Active 

route/Flt plan 

Magenta White 

Precip. 

(mm/hr): Color

0-1 Black 

1-4 Green 

4-12 Amber/Yellow 

12-50 Red 

>50 Magenta 

Turbulence White or Magenta 

56

Flightcrew Situation Awareness 

The FAA should sponsor research or assure that 

research is accomplished, to develop improved methods 

for evaluating designs for susceptibility to hazardous 

states of awareness. 

Terrain Awareness 

The FAA should encourage the aviation industry 

to develop and implement new concepts to provide 

better terrain awareness. 

Federal Aviation Administration (1992) TSO-C129 

Abstract 

This technical standard order (TSO) prescribes 

the minimum performance standard that airborne 

supplemental area navigation equipment using the 

global positioning system (GPS) must meet in order 

to be identified with the applicable TSO marking. 

General Description 

This standard includes a collection of require�

ments that are in addition to, or in lieu of, the 

requirements in the RTCA document No. RTCA/ 

DO-208, “Minimum Operational Performance Stan�

dards for Airborne Supplemental Navigation Equip�

ment Using Global Positioning System (GPS).” 

Sample Guidelines 

Waypoint Storage. 

1) The equipment navigation database shall also in�

clude all waypoints and intersections included in 

published non-precision instrument approach pro�

cedures. 

2)� The equipment shall store all waypoints, intersec�

tions, and/or navigation aids and present them in 

the correct order for a selected approach as depicted 

on published non-precision instrument approach 

procedure charts. 

3) Waypoints utilized as a final approach fix or missed 

approach point in a non-precision approach shall be 

uniquely identified as such to provide proper ap�

proach mode operation. 

4)� The equipment shall provide the capability for en�

tering, storing, and designating as part of the active 

flight plan a minimum of nine discrete waypoints. 

Failure/Status Indications. 

The equipment shall indicate, independent of any 

operator action, the following by means of a naviga�

tion warning flag on the navigation display. 

1) The absence of power required for the navigation 

function. 

2) Any probable equipment malfunction or failure 

affecting the navigation function. 

3) Loss of navigation function. 

NASA (1987) NASA-STD 3000 

Abstract 

This document provides specific user information 

to ensure proper integration of the man-system interface requirements with those of other aerospace dis�

ciplines. These man-system interface requirements 

apply to launch, entry, on-orbit, and extraterrestrial 

space environments. This document is intended for 

use by design engineers, operational analysts, human 

factors specialists, and other engaged in the defini�

tion and development of manned space programs. 

General Description 

This is a large, multi-volume work that contains 

design considerations, requirements and examples 

for manned space systems. Much of the work is not 

applicable to aviation displays. There are sections on 

displays, user-computer interaction, and informa�

tion management that can be generalized to apply to 

MFD issues. 

Sample Guidelines 

User-Computer Interaction Design Considerations. Design Principles. 

•� Feedback, which is appropriate, rapid, and predictable, should be given for each user action. 

•� Required actions or commands should be easy to 

learn, and should follow some rational or logical 

sequence. 

•� It should be difficult to make mistakes and easy to 

recover from mistakes that are made. 

•� The design should allow the crewmembers to focus 

attention on the task rather than on what they have 

to do with the system to accomplish that task. 

Display Content Design Requirements. 

Information Density 

•� Information density shall be held to a minimum in 

displays used for critical tasks. 

57

Feedback Design Requirements. 

• Use – Clear and concise feedback shall be provided to 

users as necessary to provide status information 

throughout the interaction. 

• Source – Feedback shall indicate actual function 

status. 

• Process Outcome – When a control process or se�

quence is completed or aborted by the system, posi�

tive indication shall be presented to the user 

concerning the outcome for the process and the 

requirements for subsequent action. 

• User Input Rejection – If the system rejects a user 

input, feedback shall be provided to indicate the 

reason for rejection and the required corrective ac�

tion. The location of the problem shall also be 

indicated. 

Nuclear Regulatory Commission (1996) 

NUREG-0700 

Abstract 

NUREG-0700 provides human factors engineer�

ing guidance to the U.S. Nuclear Regulatory Com�

mission staff for its: 

1)� review of the human system interface (HSI) design 

submittals prepared by licensees or applicants for a 

license or design certification of commercial nuclear 

power plants. 

2)� Performance of HSI reviews that could be undertaken as part of an inspection or other type of 

regulatory review involving HSI design or incidents 

involving human performance. 

3)� The guidance consists of a review process and HFE 

guidelines. 

General Description 

This guideline document contains hundreds of 

specific guidelines on topics such as Information 

display, User-System Interaction, Input devices, 

Alarms, and Workplace design. Although not specifi�

cally created for the aviation community, this docu�

ment has many recommendations that are applicable 

to MFD design. 

Sample Guidelines


User-System Interaction. Menu Selection.


•� Return to Higher-Level Menus. Users should have to 

take only one simple key action to return to the next 

higher level in hierarchic menus. 

Consistent Location for Menus. 

•� Menus should be displayed in consistent screen 

locations for all modes, transactions, and sequences. 

User-System Interaction. Direct manipulation. 

When to Use. 

•� Direct manipulation should be used primarily in 

tasks with actions and objects that lend themselves to 

pictographic representations and in which the ac�

tions and objects need not be modified for the 

successful interpretation of the command by the 

system. 

Managing Displays. Display Selection and 

Navigation. 

•� Sequential Steps on Multiple Displays. When ac�

tions on a new display in a sequence require comple�

tion of actions on a previous display, the user should 

be able to move to the new display only when all of 

the conditions have been met or when an intentional 

override procedure has been confirmed. 

NATO Standardization Agreement (1992) 

STANAG 3705 

Abstract 

The participating NATO nations have agreed upon 

the human engineering design criteria for controls 

and displays in aircrew stations as detailed in this 

document. 

General Description 

This standard is a short collection of general con�

trol and display guidelines. 

Sample Guidelines 

Controls/Display Integration 

1)­ Relationship. The relationship of a control to its 

associated display and the display to the control 

shall be immediately apparent and unambiguous to 

the operator. 

2)­ Design. Control-display relationship shall be appar�

ent through proximity, similarity of groupings, cod�

ing, framing, labeling, and similar techniques. 

3)­ Complexity and Precision. The complexity and pre�

cision of control manipulation and display moni�

toring shall be consistent with the precision required 

of the system. Control/display complexity and preci�

sion shall not exceed the capability of the operator. 

58

Controls. Selection 

1) Multirotational controls shall be used when preci�

sion is required over a wide range of adjustment. 

2)� Detent controls shall be selected whenever the op�

erational mode requires control operation in dis�

crete steps. 

3) Stops shall be provided at the beginning and end of 

the range of control positions. 

Visual Displays. Information 

1) The information displayed to an operator shall be 

limited to that which aids the performance of spe�

cific actions and the making of decisions. 

2) Information shall be presented to the operator in a 

directly usable form. Requirements for transposing, 

computing, interpolating, or mentally translating 

into other units shall be avoided. 

3) Failure of a display or its circuit shall be immedi�

ately apparent to the operator. 

4) Signals and display information should have dura�

tions of sufficient length to be reliably detected 

under expected operator workload and operational 

environments. 

RTCA (1991) RTCA Document No. RTCA/DO-208 

Abstract 

This document sets forth the operational goals and 

applications, and recommends standards and test 

procedures for airborne modes or any combination 

thereof. The report defines performances, functions, 

and features for 2D airborne equipment, which performs only lateral guidance, and 3D equipment, 

which performs both lateral and vertical guidance. 

General Description 

This standard contains many specific requirements 

for the RNAV and VNAV systems. The requirements 

include display accuracy limits, resolution require�

ments, TO-FROM equipment indications, waypoint 

entry and storage, and alarm limits. 

Sample Guidelines


Equipment Performance Requirements.


Update Rate. A display update interval of 1.0 

second or less shall be used. 

2D RNAV Requirements. 

Numeric display Information. 

• For en route and terminal modes, the equipment 

shall provide a numeric display or electrical output of 

cross-track deviation to at least +/- 20 nm (left and 

right). A minimum resolution of 0.1 nm up to 9.9 

nm beyond shall be provided. The display may be 

pilot-selectable. 

• The display or output shall be accurate to within 0.3 

nm up to 9.9 nm and 1.0 nm beyond or 2 percent of 

the actual cross-track, whichever is greater, refer�

enced to a centered CDI display. 

• If provided for approach mode, the display or output 

shall be accurate to within 0.1 nm, referenced to a 

centered CDI display. 

VNAV Requirements. Waypoint Altitude. 

The equipment shall provide a manual means of 

entering and storing an altitude directly associated 

with the active waypoint. The resolution of waypoint 

altitude entry shall be 100 ft or better for en route and 

terminal flight phases and 10 ft or better for the 

approach phase. This requirement shall be met over 

the altitude range as specified by the equipment 

manufacturer. 

RTCA (1996) RTCA Document No. RTCA/DO-229 

Abstract 

This document covers GPS navigation augmented 

by Wide Area Augmentation System (WAAS) for en 

route, terminal, non-precision approach and prelimi�

nary requirements for a precision approach. The 

FAA’s technical standard order (TSO) will only cover 

operations from en route to non-precision approach. 

The precision requirements are still being developed. 

This document addresses Beta, Gamma, and Delta 

functional classes. Compliance with these standards 

by manufacturers, installers, and users is recom�

mended as one means of assuring that the equipment 

will satisfactorily perform it’s intended functions 

under conditions encountered in routine aeronauti�

cal operations. 

General Description 

This is a wide-ranging and comprehensive stan�

dard concerning such topics as display symbology 

and installation and the design of control labels. 

This, along with the FAA’s TSO (C-129), AC (20-

130A), and RTCA document DO-208 all contain 

standards and requirements for GPS implementation. 

Many of the requirements are still being developed. 

59

Task 

Max # of: 

Actions Time (s) 

Return to default navigation 

screen 

1 2 

Direct to any waypoint or 

approach already in flight plan 5 10 

Select a course from a waypoint 

in flight plan 8 15 

Initiation of the missed approach 

procedure 

2 2 

Repeat the previous approach 5 10 

Initiate an approach in database 8 10 

Selecting a vector-to-final to the 

approach 4 8 

Sample Guidelines 

Controls. Control labels. 

Labels shall be readable from viewing distances of 

30 inches, under anticipated lighting conditions. 

Labels shall be unobstructed by controls when viewed 

within the angle of regard, and located next to the 

controls that they reference. Label placement relative 

to controls should be consistent across the panel. 

Terminology for labeling should describe the func�

tion of the control in meaningful terms. 

Controls. Equipment operating procedures. 

The tasks shown in the following table shall be 

capable of being accomplished within the time 

indicated. 

Society of Automotive Engineers (1969, reaffirmed 

1991) AIR-1093 

Abstract 

Numerous variables influence the legibility of aircraft instrument dial characters. This situation makes 

it very difficult, if not impossible, to establish an 

exact set of rules for optimizing all installations. 

Character size, one of the important considerations, 

can be optimized where adequate dial space exists. 

Usually this is not the case and the designer is faced 

with placing the information in a limited space while 

continuing to strive for error-free legibility. Appro�

priate minimum size requirements have been stated 

herein for guidance in air transport use. 

General Description 

This relatively old document gives such informa�

tion as the recommended minimum character height, 

width/height ratio, and stroke width/height ratio for 

dials and counters. The character size requirements 

also will apply to MFDs. 

Sample Guidelines 

Min. Char. Ht. 

Flat dials In. 

fixed .150 

moving .200 

Min. Char. Ht. 

Counters In. 

fixed .187 

moving .250 

Society of Automotive Engineers (1988) ARP-4032 

Abstract 

This document makes recommendations concern�

ing human factors issues in the application of color to 

self-luminous display instrument systems. Although 

this document is specifically intended for the appli�

cation of color to cathode-ray-tube (CRT) instru�

mentation, most portions are also compatible with 

other emerging electronic display technologies, 

whether they are self-luminous or light modulating 

devices, such as liquid crystal displays. 

General Description 

This document summarizes the research related to 

the use of color in displays. The topics include uses 

for color, number of colors, brightness, and color 

specification. 

Sample Guidelines


Uses for Color. Alerting.


• Traditional warning and cautionary colors (red and 

amber or yellow) should be reserved solely for this 

purpose, as the use of these colors for other functions 

will degrade their alerting value. 

• A single display device should not employ colors that 

are closely spaced on a chromaticity diagram as these 

will appear similar to one another and hence be 

difficult to discriminate among. 

• For critical alerting functions, color should be redun�

dant with other visual or auditory information cod�

ing methods. 

60

Uses for Color. De-Cluttering. 

Color can serve to group or organize information. 

This allows information to be transmitted more effi�

ciently as long as the number of colors used for this 

purpose is limited. A large number of colors may 

actually be counter-productive to organizing infor�

mation. The number of colors used on a single 

display should be kept to a minimum for the purpose 

of de-cluttering. 

Uses for Color. Coding. 

In general, color should not be used to code 

quantitative information unless that information can 

be divided into a small number of distinct categories 

such as has been done for color coded weather radar 

map displays. 

Society of Automotive Engineers (1995) ARP-4033 

Abstract 

A pilot-system integration approach for concept 

development is recommended. The approach em�

phasizes the fundamental need for a top-down design 

methodology with particular focus on clear opera�

tional performance requirements and functional in�

tegration. The approach is derived from established 

human factors engineering design principles. 

General Description 

As was mentioned in the introduction of the present 

document, “no collection of guidelines exists, or can 

exist, that will be able to answer each of the unique 

questions that arise.” This Aerospace Recommended 

Practice (ARP) document presents a human factors 

engineering design process that will establish a more 

disciplined design and integration methodology to 

improve the quality of the design recommendations. 

The overall concept of Pilot-System Integration 

described in this document is very similar to the 

User-Centered Design process described earlier in 

the present document. 

Sample Guidelines 

This document offers a design process to achieve 

the following objectives: 

1) Facilitate the matching of pilot skills to tasks re�

quired to operate the equipment in its environment. 

2) Identify and sequence the human factors engineer�

ing tasks for each new and revised design. 

3) Ensure consistency in human factors engineering 

processes and their outputs. 

4) Facilitate customer involvement by providing cus�

tomers with information on the nature of the hu�

man factors engineering tasks, their processes, 

output, and expertise. 

Society of Automotive Engineers (1988) ARP-4102 

Abstract 

This document recommends criteria for the design, installation and operation of panels, controls, 

and displays on the flight deck or transport aircraft. 

General Description 

The majority of this document concerns the loca�

tion and size of the overhead panel, instrument panel, 

and glareshield panel, and the operation of the con�

trols. There is however, a three page section on 

displays that has some useful information on fault 

alerts and color (the color portion is a subsection of 

FAA AC 25-11. See Sample Guidelines within that 

citation). 

Sample Guidelines 

Displays. Fault Alerts. 

• Individual fault alerts shall be provided for each 

display that is essential for continuation of flight in 

all flight phases. 

• Alerts shall include mechanical and electrical mal�

functions as well as loss of power or signal, which 

could result in a malfunction of the display. A 

distinction shall be evident between loss of signal and 

equipment failure. 

• Attitude, navigation and air data systems should 

incorporate an alert for significant discrepancies between similar systems, and between sensed and dis�

played values. Where possible (e.g., triple systems), a 

fault should be identified and indicated in an instru�

ment of the faulty system. 

Color. General. 

• Color shall have the same operational significance 

throughout the flight deck for all mechanical, elec�

tromechanical, and electronic equipment. 

• Color coding shall be supported by a redundant 

means of coding (e.g., shape, position, function) for 

all operationally significant indications. 

• Color shall be used with the aim of enhancing the 

distinction between indications, symbols and an61

nunciations, but the number of colors and extent of 

usage should be minimized to avoid loss of discrimi�

nation. 

Color. Color Set. 

• Color shall be selected from the following set of nine: 

Red, Tan/Brown, Amber, Yellow, Green, Cyan, Blue, 

Magenta, and White. 

Society of Automotive Engineers (1997) ARP 5108 

Abstract 

This document sets forth design and operational 

recommendations concerning the human factors issues and criteria for airborne terrain separation assur�

ance systems. The visual and aural characteristics are 

covered for both the alerting components and terrain 

depiction/situation components. The display system 

may contain any one of a combination of these 

components. 

General Description 

This ARP document includes sections on system 

functionality, design objectives, candidate graphic 

display options, and interface characteristics. The 

entries within the document are better described as 

general requirements than guidelines (e.g., The abil�

ity to sense flap and gear status should be provided). 

The sections on visual and aural alerts are more 

specific however. 

Sample Guidelines


Flight Crew Interface Characteristics. Visual Alerts.


1)� Two visual alerts should be provided for each pilot, 

one for warnings and one for cautions. 

2) Visual alerts should be located within 15° of the 

pilot’s centerline of vision. 

3)� The onset of the visual alert should occur simulta�

neously with the aural alert and no more than .5s 

after the system sensors detect the alerting situation. 

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