A few posts ago (#1034)
Dozy posted a link to a study related to cockpit instrumentation. That link is:
http://repository.asu.edu/attachment...010N_11979.pdf
It reports on numerous other studies and experiments involving instrumentation, including tapes. The reports are almost universally damning of the tape displays.
Here are all the relevant passages from that work, including those "favourable" to tape displays. (Bolding is mine).
Dear oh dear. So why do we have tapes today? Because they display the information better? Not at all. As you will read below, it is most likely due to the airlines preference for weight and maintenance savings!
A single digital number can be quickly and precisely perceived (Hosman & Mulder, 1997), but limitations with single readouts include poorly displaying dynamically changing data (Sanders & McCormick, 1993; Rolfe, 1965), problems with making quick qualitative estimations (or ‘check readings’) (Sanders & McCormick, 1993; Harris, 2004), and not allowing for easy comparison with reference values ...
In the following, he is initially referring to two altitude tape presentations that were trialled:
Both these moving tape concepts tested very well for speed and accuracy, presenting the required resolution and sense of temporal qualitative movement by a employing a moving linear tape and restricting the displayed range. Moving scales with fixed pointers do however have the considerable disadvantage when compared to a fixed scale and moving pointer that can display the whole range, as a quick glance will not yield an approximate picture of system state ...
Ten years after the Grether study, the USAF has a working model of the moving tape display constructed using 16-mm movie film. Testing in a Link simulator found the tape display to be workable, but pointers resulted in a superior flight performance. Further experimentation with expanded scales and more training was recommended (Mengelkoch & Houston, 1958).
In 1959 the Martin Company did extensive simulator testing of vertical tape instruments, with mixed results but predicting with design improvements that they would become valuable assets in the cockpit (Mengelkock, 1959).
NASA conducted simulator experiments with X-15 cockpits equipped with either conventional needle instruments or a vertical-scale fixed-index (ACDS) instrument suite with six tapes and found that, “missions can be carried out as accurately and successfully with the ACDS panel as with the ‘standard’ model” (Lytton, 1967, p. 12).
It was noted that experienced pilots were able to “garner a great deal of information from pointer rates and positions without having to ‘read’ parametric values,” (Lytton, 1967, p. 4) but more precision was expected with longer use of the tape displays due to their considerable gain in display sensitivity (one instrument had 40 inches of tape wound behind the window).
A problem with moving tape/fixed pointer displays is possible confusion caused by mixing this format of presentation with fixed tape/moving pointer displays in the same cockpit (known as the principle of the moving part, see Christensen, 1955; Roscoe, 1968; Johnson & Roscoe, 1972). However tape displays have been shown to be still readable when used with a variety of other instrument formats, and offer the practical advantage of a very compact form.
Sanders and McCormick conclude that:
Although fixed scales with moving pointers are generally preferred to
moving scales with fixed pointers, the former do have their limitations,
especially when the range of values is too great to be shown on the face
of a relatively small scale.
Electro-mechanical moving tape displays for airspeed and altitude entered service in transport category aircraft in 1964 with the introduction of the United States Air Force C141 aircraft, and were also deployed in the C5 fleet starting in 1969 (Hawkins, 1987). The tape-based “Integrated Flight Instrument System” (IFIS) was used in several U.S. front-line fighters (e.g. the F-105) developed in the 1960’s, as well as in the initial Space Shuttle cockpit (Lande, 1997).
Following the IFIS, small (five-inch rather than eight-inch) tape displays for altimeter and airspeed indicators were evaluated by Tapia, Strock, and Intano (1975) at the USAF Instrument Flight Center.
While the airspeed display was found to be adequate for future use, the altimeter display had some problems with the lack of range presented by the smaller size of tape. An indication of the limitations of tape displays in dynamic flight environments is seen in the midseventies when the USAF moved away from tape displays for heads down primary flight displays but retained their use for Head Up Display (HUD) symbology, seen for example in the F-15 (Lande, 1997). Air Force research presented in 1990 found HUD pointers better in basic flight performance than HUD tapes (Ercoline & Gillingham, 1990), and pointers rather than tapes are recommended by several sources for HUD applications (for an extensive review of HUD issues see Newman, 1995).
A reminder that tape displays are also not optimum when a pointer can cover the required range was seen in testing of several formats for an F-16 vertical velocity indicator (Cone & Hassoun, 1991).
The Airbus A320 introduced moving tapes with all flight
instruments presented on two eight-inch CRTs (Coombs, 1990). The Boeing Company conducted extensive research in the mid 1980’s into vertical tape instruments, finding some concerns:
They lacked relationships that were used extensively by pilots in performing flight tasks. This perception was strengthened by human factors research, which also concluded that, in general, moving scale displays are not as effective as moving pointer displays. The design constraints for the 747-400 PFD and the controversies that surrounded the vertical tape presentation provided a significant challenge to the display design engineers. (Konicke, 1988, p. 1)
Driven by explicit airline demands for the maintenance savings of CRTs over electromechanical pointers and the space requirements of matching the Airbus eight-inch screens, Boeing eventually chose vertical tapes for the 747-400.
Tape displays for airspeed, altitude, and often heading have since become standard in electronic flight displays both civil and military aircraft (Long & Avino, 2001).
The analog (airspeed indicator) display maps an abstract
conceptual quantity, speed, onto an expanse of physical space. This
mapping of conceptual structure onto physical space allows important
conceptual operations to be defined in terms of simple perceptual
procedures. Simple internal structure (the meanings of the regions on the
dial face defined by the positions of the speed bugs) in interaction with
simple and specialized external representations perform powerful
computations. (Hutchins, How a cockpit remembers its speeds, 1995, pp.
285-6).
This limitation was noted by Mejdal, McCauley and Beringer (2001):
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. (Mejdal, McCauley, & Beringer, 2001, p. 45)
In the following, he is referring to how the bugs on the airspeed tape can be for speeds that are outside the range currently displayed on the tape:
Not all the reference values disappear; the most important reference speeds are presented in an offscale manner (figure 9) when they exceed the normal range, but this is not an elegant solution. Understanding the difference between that speed and current system state now requires the operator to perform mental mathematics, rather than directly seeing the difference.
The problem is that bug values can be close to system values, but not visible to the operator as they are moved off scale. The current partial solution is to present a numerical value offscale (figure 12) but this is limited to one or two values and requires cognitive rather than perceptual processing.
Hutchins writes:
As technology changes, there is always a danger of discarding useful properties that were not recognized in the replaced technology. In their current form, the airspeed tapes that have replaced round-dial instruments in the state-of-the-art cockpits defeat some of the perceptual strategies of pilots.
The new instruments offer few perceptually salient cues that pilots can map to their concept of fast/slow in the performance envelope of the airplane. This requires pilots to read the displayed speed as a number and to subject the representation of that speed to further symbolic processing in order to answer the questions that were answered simply by looking at the earlier display. (Hutchins, 2000, p. 69)
Harris, 2004, noted, “the windowed design can be quite poor at providing the pilots with anticipatory information. On the electromechanical counter-counter altimeter, the altitude ‘bugs’ were always visible.” (p. 87). Although new displays have been tested before entering service into aircraft, the aircraft cockpit may not yet be fully mature.
Billings, 1997, reported that there were, “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.” (p.34)
Glass cockpits allow designers to present huge amounts of data, indeed:
Information management technology has all but erased the problem of
insufficient data in the system. Data, however, is not information. It
becomes information only when it is appropriately transformed and
presented in a way that is meaningful to a person who needs it in a given
context. (Billings, 1997, p. 42)
Being able to present more bug and reference values graphically on the tape display would fit the principle of proximity compatibility (Wickens & Carswell, 1995; Wickens & Andre, 1990), a concept that is broken by (the common current solution) displaying important values numerically next to a graphic tape.
Proximity compatibility is a movement towards expanding a single perceptual object display rather than forcing the human to cognitively integrate several inputs (Carswell & Wickens, 1987).
Instrumentation has moved from being initially designed around mechanical practicalities (e.g. the pitot pressure driven round airspeed dial), to more humancentered electro-mechanical presentations (e.g. the tape airspeed indicator), to today’s fully electronic computer graphic presentations (e.g. the A320 PFD with its dynamic bugs and limitation arcs added to the tape display). We may now be overdue for a redesign of these displays to more match human perceptual and cognitive abilities.
Writing in Science, Hirschfeld (1985) noted that, “more effort in
display psychophysics will be needed to match instrument output to brain input.