A LABORATORY COMPARISON OF TRACKING WITH FOUR FLIGHT-DIRECTOR DISPLAYS

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Abstract
Tlio following flight-director displays were compared in tho laboratory on a simple aircraft simulator under controlled conditions of noiso and ambiorit illumination: (a) Streaming Lights which presented errors in the flight of the ‘ aircraft ’ by tho direction and rate of apparent movement of streaming lights; (b) ’ Barber's Poles ’ which presented errors by the direction and rate of translational movement of a white helical strip along a black, rotating polo; (c) Flashing Lights attached to the simulator, or to a helmet worn by tho subject, which presented errors in each dimension by the position and rate of flash of a single flashing light; (d) l.L.S. Meter which was intended to represent, a Zero-Reader display and presented errors by the position of two pointers mounted at right angles to each other. All these displays were designed to present navigational information to a pilot while he was scanning the outside world, and all except the last presented tho information in peripheral vision. In continuous tracking, the time off target with Flashing Lights or tho I.L.S. Meter was about a quarter of the time off target with either tho Streaming Lights or tho Barber's Poles. In correcting sudden errors, Flashing Lights on tho Helmet gave quicker responses than any other display which was investigated. This was presumed to bo the result of the high attention-getting value and the immediate directional indication of the signals. The weakness of Flashing Lights on tho Helmet, which also applied to the Barber's Poles and Streaming Lights, was in presenting information on the size of errors. The I.L.S. Meter was the best display in this respect, although it did not always attract the man's attention as soon as it indicated an error. The combination of Flashing Lights on tho Helmet and tho I.L.S. Meter produced tho quickest corrections recorded during the experiments. Reaction time to signals presented on a central display increased about 40 per cent when attention had to be paid to any of the flight-director displays. Tho size of tho increase was about the same whether simulated control of tho aircraft was carried out or not while performing the central task. This suggests that it was tho need to attend to the additional channel of information, rather than simultaneous demands for action, which interfered with the central task. Performance with Flashing Lights on the Helmet and Streaming Lights showed only a small and not statistically significant adverse effect from occasional rotation of the head and eyes of 70°. Sideways movements of tho head altered the angle subtended at the subject's eye by the Barber's Poles mounted horizontally fore and aft to display information on altitude. This changed the apparent rate of movement of the display and the apparent display-to-cantrol ratio, and thus caused the subject to miss small errors occasionally, or make control movements of the wrong size. In addition, with tho Barber's Poles the display-control directional relationships changed as attention was directed from one end of the azimuth display to the other. This could occur in on aircraft when the pilot rotated his head and eyes, and might be dangerous.

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