Preventing G-induced loss of consciousness: 20 years of operational experience.

INTRODUCTION Although anecdotal reports of G-induced loss of consciousness (G-LOC) in military aviation date back to before 1920, regular reporting did not begin until 1982. The effectiveness in the operational setting of G-LOC preventive measures, such as positive pressure breathing for G protection (PBG), has not been studied. METHODS We use the term "crash" to represent an event where the aircraft was destroyed and "incident" to define those events where the crew reported a G-LOC episode and the aircraft was not damaged. Data on G-LOC crashes, incidents, and aircraft sorties (number of take-offs) were obtained from the USAF Safety Center database for FY 82-01. RESULTS During FY 82-01, there were 29 G-LOC crashes while those aircraft at risk of G-LOC crashes flew a total of 13,959,816 sorties. Poisson regression showed a non-significant decrease in crashes with an incidence rate ratio (IRR) of 0.096 (CI 0.89-1.03) (4% per yr). G-LOC crashes decreased from 4.4 per million flight sorties (PMFS) to 1.6 after the implementation of anti-G-LOC training programs beginning in 1985. However, G-LOC crashes remained unchanged after implementation of PBG in 1995. In contrast, incidents showed an IRR of 1.04 (CI 1.02-1.06) for G-LOC incidents, an estimated increase of 5% per yr. DISCUSSION The physical/mechanical limitations of PBG, risk homeostasis, and the possibility that G-LOC rates have reached their asymptotic minimum are all discussed as possible explanations for the failure of PBG to decrease G-LOC crashes.