Drinking occasionally or regularly by the pilots, but restricting it to couple of small pegs, remains a matter of individual choice and social acceptance. But aviation safety and alcohol do not go together. In an interesting instance at Heathrow Airport, a Delta Airline pilot forgot what his destination was! His blood alcohol levels were found to be more than four times above the permissible levels.
Apart from being a cerebral depressant, alcohol affects the flying performance by making one prone to hypoxia and diminishing psychomotor and visual functions. Episodes of spatial disorientation are more likely after consumption of alcohol. so also combat pilots have reduced ‘G’ tolerance. This makes pilots prone to mistakes and errors, sometimes resulting in accidents.
Alcohol is known to affect almost all the systems of the body but the central nervous system is affected most – even in low concentrations. Finer grades of discrimination, immediate memory, concentration and judgment, and finer skills are dulled. Reaction time increases. The drunk may become uncritical, casual and self satisfied. There is also an evident lack of inhibition after alcohol consumption. This is due to removal of the higher cerebral control over the lower centres of the brain. So also, there is a tendency to disregard rules and conventions and the person may become argumentative. All these effects are dependent on the level of alcohol in the blood.
A single drink contains about 12 gm of alcohol, which is usually equivalent to 12 oz. Beer [7.2 proof, 3.6%]; 4 oz. non-fortified Wine; or 1-1.5 oz. Whisky, Gin, or Rum [80 proof, 40%]. It is absorbed from the gut (stomach 10%, remaining from small intestine) in 2 to 6 hours depending on whether it is taken on empty stomach or with food, which delays absorption particularly if it is greasy e.g. fried snacks. Peak concentrations are reached between 30 to 90 minutes later. Alcohol is distributed in all the body tissues, and tissues with greater water content have a higher level of alcohol. 90% of consumed alcohol is oxidised in the liver, and 10% is excreted unchanged by the kidneys and lungs. About 2-3 Oz. of drinks, like whisky or rum are eliminated in an hour. Thus, if one takes three small pegs (3 Oz.) of whisky/rum alcohol will disappear from blood in 4½ hour plus the time required for absorption depending on the total period over which the person had consumed and whether he had taken it on empty stomach or with snacks. Therefore, the total period for metabolising alcohol is anywhere between 8 to 12 hours.
A controlled study on the effects of alcohol on flying was conducted among pilots, who were given three small pegs (3 oz) of whisky/rum along with snacks over a period of one hour and were assessed for (simulated) flying skill, reaction time, in-flight calculations and handing of emergencies five and seven hours after intake of alcohol. Majority of pilots committed mistakes after five hours, some of which were of serious nature like failure to lower undercarriage or faulty emergency procedures which could have resulted in accidents in actual flight situations. Some pilots were found to commit minor mistakes in calculations even after seven hours.
ICAO regulations wisely mandate a delay of 12 hours between ‘bottle to throttle’ or after the last drink and the first take-off. Ideally the safe limit of alcohol in blood is Zero. Hence, pilots must ensure that even if they drink to relax or unwind, the time interval between the last drink and flying should be such that blood level of alcohol should fall to zero and so also the effects of congeners should disappear. Or else, we have the situation of being in the arms of Bacchus and compromised aviation safety.
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