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Thu, Jan 30, 2003

More on .004% BAC Pilot Story

We must have started something.

Since publication of yesterday's story, which detailed how an American Airlines pilot was kept from the cockpit on a Little Rock to St Louis flight Monday, we've gotten a lot of feedback from highly-qualified medical experts.

Interestingly enough, our industry contacts won't call back; the folks who make the equipment don't want to talk. On another front, the Allied Pilots Association spokesman, Gregg Overman, said the union's duty is to protect the pilot; but that he actually didn't have any information to give us, on this particular case.

That's OK, though, because we're really looking at the science involved.

We asked, in our article, whether .004% BAC, as determined on typical US airport (or police) analysis machines, could be a reliable number. One doctor wrote us, "...0.02%... constitutes the lowest reliable limit on their zero-tolerance scale."

Another wrote, "0.004% [is an] insignificant, minuscule concentration. I doubt it is possible with commonly used standard techniques to measure -- with any degree of precision -- BAC at such low levels. And why bother?"

We wondered if something other than the ingestion of alcohol could deliver such a reading. Another doctor wrote, "Ethyl alcohol and some other alcohols can be generated at very low levels by bacterial fermentation in the human gut. This is not a reliable way to get drunk as alcohols are carbohydrates and are quickly metabolized at a rate of about 0.017% per hour (typically 0.015 for males and 0.018 for females with variation on the degree of enzyme activation due to repeat exposure-zero order kinetics apply above 0.010%). It is also possible for someone to consume a small amount of alcohol and get a BAT of 0.004%. Using the Widmark equation of A=WRC/0.8,  where A=volume of pure ethyl alcohol consumed, W=body weight, C=BAT and R=distribution ratio, or measure of fat. Typically R=68% for males and 55% for females on average. Solve this equation for a 70Kg male, you get 2.38g of pure alcohol, or about half a teaspoon. Considering that some mouthwashes are up to 25% alcohol, this is well within a swallow... So spit it out." So, if you drink mouthwash, you can get drunk; but who would?

As to the question of whether a BAC of .004% would have any measurable effect on a pilot's ability, we got the following: "Based on experimental research, it is generally agreed that a BAC as low as >0.02% can impair a (young, untrained) pilot and reduce his IFR flying skills. At BAC >0.04%, such impairment can be measured in trained pilots. Many Civil Aviation Authorities around the world have set 0.04% as a legal limit for flying." Well, the pilot in question had 1/5 of that ".02%" on his breath...

Here's an interesting one: alcohol on the breath

We wondered if the security agent who said he detected "alcohol" on the pilot's breath could be believed. The answer is technically, "no" -- but, for all practical purposes, a resounding, "yes." Here's a few answers:

"The screener could not have detected alcohol on the pilot's breath because alcohol has no aroma detectible by humans." He explained, "We can smell the metabolic products of alcohol, acetaldehyde and acetate, which provide that fruity aroma. Same aroma is produced if you are seriously dieting, as utilizing the body's fat reserves also produces some of these compounds. The screener's nose can easily sense concentrations on the order of 5 parts per million." How good is that? "Not as good a dog, but good enough," he said.

Another doctor, who must like the same kind of candy we do, wrote us, "Oh yes - our sense of smell is very efficient. Perhaps the screener's nose registered a drop of alcohol from a piece of candy flavoured with rum or similar."

From a beer-drinking country: "One more comment on the smell of alcoholic beverages in the breath and the screener's good nose: in beer-drinking countries (like ____) everyone is generally aware of the fact that even a small amount of beer can easily be smelled in the breath; this is true also for non-alcoholic beer. If our unfortunate pilot had had a glass of 'non-alcoholic' beer, which usually contains about .5% alcohol, he might smell beer for the next half hour and even have ingested enough alcohol to get a BAC of .004%." A comment on non-alcoholic beer, from another doc: "I would consider 'non-alcoholic' beer 30 minutes before flight the same as adjusting a roof mounted antenna 30 minutes before a lightning storm. Good odds, bad judgment."

Doctors and politics

The implications of such actions gave some of our expert friends a chill. One told us, "The story about an American Airlines pilot, if accurately reported, gives grounds for concern by us all. ...this grounding is not based on any defined limit and may well be due to error." [We should point out that the pilot was grounded merely for this flight, as far as we know --ed.]

One more weighed in with this advice: "If we have limits, fair enough, let them be applied. If there are reasable grounds for doubt, play safe and check again. On the evidence we have seen so far, this case appears ridiculous. has just struck me that grounding a pilot for a breath alcohol of .004% is like being arrested for speeding when driving at 4 m.p.h. in an urban area."

One last comment, from a doctor who didn't approve of our quick-and-dirty method: "Pandering to the current interests of the press as a surrogate for the perceived best interests of the flying public can make for some very bad and very unfair aeromedical decisions." [We agree --ed.]



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