Pitch-Plane Angular Displacement Perception During Helicopter Flight and Gondola Centrifugation

During hovering with a helicopter, an involuntary change in attitude (during brownout) results in reduced lifting force and a horizontal acceleration component. This movement pattern is difficult to perceive via the otolith organs. If the angular displacement occurs rapidly, it will, however, activate the semicircular canals. The major aim of this study was to establish to what extent pitch-plane angular displacements can be perceived based on canal information when there is no tilt stimulus to the otoliths.

In a helicopter, 9 nonpilots (N) and 8 helicopter pilots (P) underwent 5-6 pitch-forward displacements (magnitude 14-33°, angular velocity 2-7° · s^-1). In a swing-out gondola centrifuge, 9 N and 3 P were exposed to a similar canal-otolith conflict (acceleration, seated centripetally) with four displacements of 25° and two of 60°. The visually perceived eye level (VPEL) was continuously recorded using an adjustable luminous dot in darkness. For each helicopter dive and centrifuge run the gain was calculated as the ratio (VPEL deflection)/(displacement of helicopter or gondola).

In the helicopter there was no difference between N (0.28 ± 0.13) and P (0.36 ± 0.22). In the centrifuge the gains were 0.34 ± 0.18° (25° displacements) and 0.30 ± 0.16° (60° displacements). Values obtained in the helicopter did not differ significantly from those in the centrifuge. There was a correlation between data obtained during the 25° and 60° displacements in the centrifuge.

There was a pronounced underestimation of pitch angular displacements in a helicopter. The interindividual variability was considerable. Gains for perceived displacement were similar in helicopter and centrifuge. Tribukait A, Bergsten E, Eiken O. Pitch-plane angular displacement perception during helicopter flight and gondola centrifugation. Aerosp Med Hum Perform. 2016; 87(10):852-861.