Don't know what the limit for pilots is, but with your standard intoximeter,breath is exposed to infra-red radiation at a wavelength of 3.2 microns at which ethanol absorbs the radiation in accordance to the Beer Lambert law..i.e, The absorbance is directly proportional to the concentration of ethanol. Strict precautions are taken to make sure that the machine is accurate and precise. To ensure this in addition to two breath tests,the machine is equilibrated twice with background air and twice with air containing an ethanol level of 35% (the legal limit for drivers).A built in compensation is made for the presence of propanone which can come from diabetics. I reckon that there might have been something wrong with the machine and if a blood test was subsequently taken this would have sorted out any discrepencies made by a machine. This is largely irrelevant but might clear up some mysteries about proceedure.
If he was clear second test....and blood test, he was clear....the bloke was innocent...double line....end of story!
Machines can be wrong and there are back-ups. HE WAS CLEARED!!!!