Since the beginning of Aviation, instruments have been designed to provide the pilot with the information needed to control the aircraft. During the past 30 years, pilot involvement in aircraft navigation, guidance and control has shifted from manual control to supervision of the navigation system. The domain of digital avionics provided the enablers for this shift, and several important developments started already over half a century ago. One aspect of these developments concerns the instruments designed to provide the pilot with the required information. When considering today's systems, it is not immediately obvious that for several of the currently implemented concepts there have been other, competing ones that for some reason did not make it. It may come as a surprise that some of these alternatives are conceptually superior but required technology that at the time was not sufficiently mature for implementation in an aircraft. In this paper, the history of some promising alternatives is provided, and it is speculated why these ended up as missed opportunities. To illustrate how certain instrument / data presentation concepts are better suited to provide the required guidance, navigation and control information for both skill and knowledge-based involvement of the pilot, a classification based on the inner-, directional-, and outer-loop closure of the navigation function is used. It is argued that due to the increased complexity of the pilot's supervisory control task in a future air-traffic environment, some of these alternatives need to be reconsidered as a basis for decision support, and it is illustrated what opportunities exist.
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