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vary with the sex and size of the individual drinker. Generally speaking, the same amount of alcohol will raise the blood alcohol level more in a smaller person than a larger one, and more in a female than a male.
Another useful rule of thumb is that alcohol is metabolized at a rate of about 0.016 percent per hour. This rate of metabolism is relatively constant among all individuals, but can be slower in persons with liver damage who don’t produce normal amounts of the enzyme that is responsible for alcohol breakdown, or persons who, for genetic reasons, produce slightly different and less effective versions of those enzymes. Another way to look at this is to understand that it takes a little over an hour to metabolize one standard drink. So if you drink more than one standard drink per hour, your blood alcohol level will rise faster than your body’s metabolism can lower it.
Figure 1 shows the blood alcohol concentrations at various times after ingestion of one, two, three or four drinks over a one-hour period. The results are given in mg percentage. (To convert to BAC concentrations, divide by 1,000 so a concentration of 20 mg percent is equal to a BAC of 0.02.) Notice that it took over four hours for the subjects who had four drinks in rapid succession to get back to the 0.04 FAA standard. Had the person continued to drink over the next few hours, it is quite possible that it would take longer than
eight hours from the last drink for their blood alcohol level to drop to below 0.04. In fact, if you had nine drinks over a four-hour period, you would be above the FAA limit eight hours after the last drink. Admittedly that’s a lot of drinking, but remember that the FAR also prohibits acting as a crew member when under the influence of alcohol. That could be interpreted in many ways including suffering from a bad hangover that was impairing your performance.
It’s clearly important to limit your alcohol intake when a flight is on the horizon. Not only should you consider modifying the eight-hour rule to 12 hours, but you should limit your intake so that all the alcohol is out of your system several hours prior to acting as a pilot. KA
The items discussed in this column are related to experiences by Dr. Seckler in his many years as an AME, and made hypothetical for the article. Any information given is general in nature and does not constitute medical advice.
About the Author: Dr. Jerrold Seckler has recently retired after practicing medicine (urology) for over 40 years and as an active AME for 25 years. He has over 6,000 total hours, 2,200 of those in his 2001 Cirrus SR22. He is an ATP, CFII, former COPA Board Member and a ground instructor at CPPPs.
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NOVEMBER 2015
KING AIR MAGAZINE • 21