I think this whole thread is what is called a "wind-up" on PPRUNE. There's not a single hint the US is headed to this. Never the less -

[quote=The Dominican

Wrong again, what this does is that it keeps any instance where a pilot might be over the limit to crew a flight within the company and it wouldn't go as far as being a legal matter since any potential problem would be detected before the authorities get evolved.[/quote]

In the US, it is a violation of federal law to report for duty under the influence. Each year each air carrier sends a report to the DOT covering how many drug and alcohol tests were done, how many were pre- employment, random, for cause, etc, how many were positive and for what. In addition, the carrier has two days to inform the Federal Air Surgeon if anyone with a medical has a positive test.

The alcohol testing protocols are pretty good. If a screening test gives a result at .02 or greater, there's a 15 minute time period to give the subject time to exhale all the alcohol from mouthwash, etc and during which the machine is checked for calibration. If the second confirmation test is still at or above .02 the subject goes home and if the result is .04 it's a positive.

Totally useless trivia - in the ~20 years there has been drug testing of pilots, there has NEVER been a positive for PCP.