I, as part of my second occupation, have to perform drug and alcohol screening everyday in the medical centre of a construction site. The victims are picked at random (some 5% of the workforce). They recently have added a fatigue test by way of a computerised eye reaction measurement. We can do urine and saliva tests for drugs, but only after a significant event. All this was accepted by the unions as fair, considering the high risk of injury.
So as for the results? Most blow less than .05 despite being borderline alcoholics
. They are given a second test a short time later and can continue work if back at 0.0 (most). Very few blow over .05 (who are invited to rest for the day elsewhere). The fatigue test is very hit and miss, if they show positive they take the test again and usually pass
Upshot is that fatigue testing is unreliable and the breath test needs a fair consumption to show anything (we test this regularly, I myself needed three pints to get .01)
As for the need to test pilots, can we not rely on multi crew operations to police themselves?