Apparent instrument horizon deflection during and immediately following rolling maneuvers

There have been recent reports by pilots of apparent visual bending or bowing of instrument horizons during and immediately following ascending rolling maneuvers in the F-14 aircraft. The present study investigates the probability that normal reflex actions may partially account for the illusions cited in these reports. The results of this study suggest that the vestibulo-ocular reflex (VOR) can produce an apparent deflection of the instrument horizon (actually an apparent flicking back and forth) during and after roll maneuvers involving high peak angular velocities. This perceptual aberration could disturb a pilot attempting to use his instrument horizon and could lead him to suspect instrument malfunction. The reported distortions of the instrument horizon could be the result of the VOR, which tends to stabilize the eye relative to the Earth during angular acceleration of the head, and therefore reflexly displaces the eye relative to objects such as flight instruments that move with the head.