Signs and symptoms during supra-tolerance +G(z) exposures, with reference to G-garment failure

+G(z) exposure above the tolerance threshold typically induces a sequence of symptoms/signs, with loss of: peripheral vision, central vision (black out), and consciousness (G-LOC). The aims of this study were to investigate: 1) whether G history influences latent time to, or sequence of, symptoms/signs upon G exposures exceeding the tolerance threshold; and 2) how pilots respond to a sudden loss of pressure in the anti-G garment (AGG) in flight-like scenarios.

There were 14 subjects who were exposed to rapid onset rate +G(z)-time profiles, with plateaus 1 and 2 G above the relaxed tolerance level, without initial pressurization of the AGG (NoAGG) and when losing AGG pressure after 10 (AGG_10) and 120 (AGG_120) s at the plateau. Simulated target-chase flights during which AGG pressure was released were performed by seven pilots; the pilot was instructed to behave as during real flight.

Latent time to symptoms was shorter at +2 G than at +1 G, and shorter in AGG_10 and AGG_120 than in NoAGG. In AGG_120, 43 and 64% of the subjects experienced serious symptoms (black out, Almost LOC, G-LOC) at +1 and +2 G, respectively, compared to 21 and 54% in AGG 10 and 7 and 29% in NoAGG. The incidence of A-LOC/ G-LOC was higher in AGG_10 and especially in AGG_120 than in NoAGG. During the target chase, one pilot did not notice the pressure loss, one experienced G-LOC, and two A-LOC.

The risk of serious consequences of G exposure exceeding the tolerance level appears to be greater when G-garment failure occurs after a prolonged than after a brief exposure.