The right attitude


The FDAI (Image Source: NASSP)

Apollo, engineers and astronauts

One of the more interesting human factors aspects of the Apollo program was the development of the attitude reference for the Apollo Command Module (CM) and Lunar Excursion Module (LEM). The Flight Director Attitude Indicator (FDAI) was used to display the spacecraft attitude, similar to a artificial horizon of an aircraft.

The original intention of the engineers at the MIT Integration Lab charged with developing the interface was to drive the display directly from a gimbal on the inertial reference platform. Of course this meant that the reference plane would be to the distant stars and when the spacecraft were orbiting the moon or earth the attitude reference indicator would be also be slowly rotating.

The astronauts of course were horrified by this approach as from their aviation background they expected the attitude reference to be aligned to a local lunar or earth horizon. A attitude reference aligned to the star field provided rotating as the spacecraft orbited was both of little value and downright disturbing. However from the engineers perspective a ball tracking the local vertical would also provide no real value during the launch sequence as the spacecraft pointed vertically up before it pitched over into its orbital trajectory.

In the end the astronauts won the argument and a second mode of attitude reference indication was provided that gave a stable non rotating reference, by introducing a pitch command into the FDAI of the same magnitude as the orbital period. When a spacecraft maintained a constant face towards the body it was orbiting a fixed attitude reference would be provided. This struggle between the engineers on the one hand and the astronauts on the other perfectly illustrates the importance of understanding cultural cliches or precedents (Lewis 1969), and recognising how we rely on them for effective coordination of action between humans and automation, which in turn is designed by other humans.

Where designers and users share a common set of precedents, for example ‘red is for warning’, or ‘move the throttle forward to accelerate’, then a system designed with these in mind will meet with the users expectations. Where designers depart from these shared precedents, because of the perceived novelty of application or technology, they can also introduce significant interaction problems with the system of concern. Design of the human machine interface is both a value judgement laden and culturally context sensitive process. A fact that  many engineers seem to be uncomfortable with.


Lewis, D.K., Convention: A Philosophical Study, Harvard University Press, 1969.

One response to The right attitude


    You will be interested in this:

    Click to access 08-02.pdf

    A helicopter pilot in the Osprey has to get used to the ‘collective’ being a ‘throttle’ and working in the opposite sense.