Abstract

Advances in computer technology and Compact Disc-Read Only Memory (CD-ROM) have given way to the advent of the Interactive Electronic Technical Manual (IETM). IETMs have compressed the numerous volumes of text into just a hand full of CD-ROMs loaded with the text, sound and video. This brings into play new human factors issues. What is the proper and most comprehensive way to display this information? Is it safe to assume that the user can use the software efficiently? Can an electronic system be reliable enough to convey the information without being confusing or misleading? This paper will try to answer these questions and address other problems faced, with the introduction of IETMs.

Introduction

Recently it has been more widely acknowledged that aircraft maintenance requires human factors resources like with those that have been applied to other aspects of aviation. The general causes of human error and the means for error prevention, originate in basic human capabilities and limitations (Royal Aeronautical Society, 1991). In aircraft maintenance there is a small margin for error, for a set of tasks done day in and day out. A set of tasks that can determine the outcome of hundreds of passengers. To the aircraft maintenance technician (AMT), these tasks can become routine causing them to inadvertently skip steps in a maintenance procedure. Manufactures have produced volumes and volumes of technical manuals to prevent this, but consequently they have created a time consuming hurdle for AMTs. This hurdle causes some AMTs to become complacent and perform various tasks without the aid of a technical manual.

Advances in computer technology and Compact Disc-Read Only Memory (CD-ROM) have given way to the advent of the Interactive Electronic Technical Manual (IETM). IETMs have compressed the numerous volumes of text into just a hand full of CD-ROMs loaded with all the text plus, sound and full color,video- all at the "click" of a mouse. Electronic manuals allow the user to have much better control of the revision status of the manuals. Instead of having to remove and replace pages or manuals, one could insert a new CD-ROM, costing only a fraction of the original price of revision. This cost saving feature has attracted many airlines to IETMs.

In an industry where time is money, airlines have spent the last several years researching the feasibility of IETMs. They have been examining the different input and output devices, such as: cathode-ray tubes, keyboards, touch screen, pointing devices, voice recognition, and headset mounted displays. United Airlines expects to move to electronic technical manuals, for its fleet of more than 560 aircraft, during 1996 and 1997 (Aircraft Maintenance International, 1995). The Federal Aviation Administration (FAA), has to approve the use of IETMs before any of the airlines in the United States replaced their volumes of manuals.

IETMs: Hypertext and Hypermedia

IETMs are based on the computing principles of hypertext and hypermedia. Hypertext involves the text component of IETMs, while hypermedia is a hypertext application assisted by multimedia accessories. The simplest way to define hypertext is to contrast it with traditional text like a book. All traditional text...is sequential, meaning that there is a single linear sequence defining the order in which the text is to be read...Hypertext is non-sequential; there is no single order that determines the sequence in which the text is to be read. (Nielsen, 1990)

Hypertext presents several different options or screens, called nodes. The user determines which of them to follow by using a link. A hypertext link connects two nodes, from an anchor node to a destination node. An excellent version of a hypertext system is the World Wide Web (WWW) on the Internet. This system is an elaborate matrix of nodes and links, never restraining the user to a set sequence of events, making a search for information more efficient. The current popularity of the WWW is not totally due to this feature, it is the visual and audio interaction, which attracts users from around the world. This interaction is called hypermedia.

Hypermedia is a hypertext system that is enhanced by the addition of graphics, sound and video. The addition of these enhancements help the user understand the text better, assuming the graphics, sound and video are clear. In a hypermedia system, a text node can be linked to a video, then the user can select to a part shown in the video and an exploded view of that part would be shown, all while the text is being read to him/her by the computer. The users and designers, of a hypermedia system, have to pay a price: electronic storage space.

CD-ROM

A hardware problem is the storage space needed for the multimedia in hypermedia. For example, a single color television image takes up 105 kilobytes of storage, meaning that a minute of video would take almost 200 megabytes (Jonassen, 1989). This makes it impossible to store hypermedia, with extensive video, on traditional computer disks. On the other hand, optical devices such as CD-ROM allow for the storage of large amounts of data. A single CD-ROM can store between 550 and 650 megabytes of data, which is equivalent to between 500 and 1000 text only books (Jonassen, 1989). "A CD-ROM can be produced for $2 plus a one time fee of $1500 for the master disk used in pressing the disks." (Nielsen, 1990).

These features makes hypermedia and hypertext attractive, take for example the documentation for an F-18 fighter. The documentation consists of 30,000 pages (Ventura, 1988) and requires 68 cubic feet of storage space when printed on paper, compared to the 0.04 cubic feet the same information takes up when stored on a CD-ROM hypertext. It also saves on the cost of updating the information. Instead of sending new pages to be inserted in the various binders, a new CD-ROM could be pressed and shipped all for about $2 plus shipping costs.

User as Reader

The user of an IETM system will be reading material from a CRT computer screen or other output device. Therefore, what is known about reading and how it relates to screen displayed text must be considered. (Reading, related to screen displayed text will be discussed in the CRT Computer Display: Readability section.)

When reading, light enters the eye through the cornea, passes via the aqueous humour to an opening in the iris known as the pupil where it is focused by the lens. From here it passes through the vitreous humour to the innervated portion of the eye called the retina. From the retina, the light signal passes down the optic nerve to the brain (McKnight, 1991). As the user reads a document, their eye movement may feel smooth but actually it consists of a series of rapid jumps and rests, termed saccades and fixations. Saccades last approximately 25-30 milliseconds, fixations 200-250 milliseconds, so the eyes are stationary for about 90% of the reading time (McKnight, 1991). The number of fixations and time per fixation increase with text difficulty, therefore an IETM system's text must be detailed and clear, but not difficult to read. This would cause the AMT to take extra time reading, which could have economic consequences for an airline.

Computer Hardware

Interactive electronic technical manuals need to run on a computer and are therefore highly dependent on the available hardware technology. Many of the complaints people have against hypertext applications are not directed against the principle of hypertext but are based on user interfaces and the current generation of technology. In a field study of hypertext, 33% of the users complained about the very fact that the hardware was not as convenient as paper (Nielsen, 1990). In the application of IETMs, this opinion can become a troubling fact.

The Federal Aviation Regulation's (FAR) Part 43 specifies that an AMT must have in his/her possession the current maintenance manual, pertinent to the procedure that he/she is performing. Meaning that an AMT has to go to the IETM, research the procedure, watch the various videos, read the text, then print a copy. Assuming that the hypermedia system is designed with quick searches in mind, an AMT has to make sure he/she has retrieved the proper and complete information, if not the process will have to be repeated. This situation can have severe implications in an industry where time equates to money. Another element that can be involved with the above scenario is the economic and enviromental impact of the repeated printing of maintenance procedures. A portable system would eliminate the need for paper.

The "Private Eye" System

A key component in any hypermedia system is the mode by which the output is conveyed. A display developed by Reflection Technology called the " Private Eye" is worn by the user on a headset. It is a miniature display (1x1 inch) that is placed in front of the user's dominant eye, and creates the illusion of a full (10x12 inch) display (Shepherd, 1991). A hand held computer, using a "smartcard," a credit card sized plastic card which contains one megabyte of text, enough to store the King James version of the Bible, would provide the data for the display. Implementation of the "Private Eye" is not yet practical for aviation maintenance. "Use of the system demonstrated that the headset is awkward and keeping the display in the right location for viewing requires constant attention. In addition, looking at the display for any length of time becomes uncomfortable (Shepherd, 1991)."

CRT Computer Displays: Readability

The most widely used medium for hypermedia is the CRT computer display. Readability formulas based on sentence length, word length or other characteristics have been a continuing subject of research and various measures are used in practice to estimate the difficulty of reading a particular piece of text (Glushko, 1991). Much of the research has considered the effects on readability of presenting text on computers, but only few studies have directly addressed the readability of hypertext.

Studies have compared the reading speed from the screen of a CRT with the reading speed from paper and have found that screens are 30% slower (Gould, 1984). Proofreading is also effected by the use of a CRT, a two page text was proofread 38% slower on a CRT. Dr. J. Gould tested an advanced type of computer display utilizing anti-aliasing fonts. Anti-aliasing is a computer graphics technique of using greyscales to smooth over the jagged edges of traditional black-and-white fonts. The results were impressive: CRT reading speeds increased to practically the same levels as paper: 204 words per minute vs. 206 words per minute, respectively. The accuracy of finding errors increased also, when compared to paper: 79% vs. 81% (Gould, 1987). Dr. Gould's findings have been applied to current computer displays and applications, therefore making the use of CRT computer displays reasonably reliable for AMTs.

CRT Computer Displays: Screen Size

Larger CRT screens allow users to see more hypertext material at the same time and allow room for various extra user interface features such as permanently displayed diagrams. A research group had users read a hypertext in order to answer questions on it (Shneiderman, 1987). Users who used a screen displaying 34 lines of text at a time performed faster than users who could only see 18 lines, 8.6 minutes vs. 9.8 minutes. The same research group also conducted experiments with subjects reading program text from various screen sizes using ordinary text editors. For a 22 line display answering the questions took 9.2 minutes, for a 60 line display it took 7.9 minutes, and for a 120 line display it took 6.6 minutes (Shneiderman, 1987). All these experiments confirm the belief that bigger is better when it comes to computer screens.

Input Devices

Various forms of input devices and interfaces exist in the computer industry today. The proper and most efficient tool must be used in IETMs, so that the system will save time. Hypertext systems can incorporate keyboards, mice, touch screens, and the human voice as an interface devices. Keyboards are an excellent means by which to input data and text, but may not be the best choice for hypertext systems. Being graphically based, an IETM system would require the user to select icons, access data. This could be done with a keyboard, but would require numerous keystrokes and there would be more room for error. An answer to this problem is a pointing device or mouse. Almost all current hypertext systems are used with a mouse as the primary pointing device and a keyboard as an input device. Several human factors studies of computer interfaces in general have shown that the mouse is a good pointing device (Nielsen, 1990). For some hypertext applications the mouse might be too fragile to be used. In these situations it is common to use a touch screen. A touch screen does not have the tactile feedback that a keyboard or mouse have. Also links, in the form of icons must be spaced far apart so that a wrong icon would not be touched. Some applications have worked around the feedback problem; the "button" or icon change color or intensity when touched and their is audible feedback.

Voice recognition in computers would be the best interface, assuming the user could speak, know what to say or ask and was verbally fluent in the language the system used. The current technology available is not enough to make it the primary interface for a hypertext system. It would require the user to "train" the computer to recognize his/her voice. Which may be practical for a single user, but in a IETM system, where the users would be numerous, it would require an enormous amount of time and electronic storage space. Voice recognition may become the number one interface in the future but for now the keyboard and mouse combination are the best (McKnight, 1991).

IETM/Hypertext Usability

The single most important factor in the design of an Interactive Electronic Technical Manual is the human and the computer working together to accomplish a set task. The computer's hardware and software must be user-friendly. Usability is traditionally associated with five parameters:

• 1) Easy to learn: The user can quickly become comfortable with the system.

• 2) Efficient to use: Once the user has learned the system, a high level of productivity is possible.

• 3) Easy to remember: The user is able to return to the system after a period of time and work with the system without retraining.

• 4) Few errors: Users do not make many errors; if they do, they can easily recover from them.

• 5) Pleasant to use: Users are satisfied by using the system (Nielsen, 1990).