Here is the answer already given by
hamster3null
17th Aug 2015, 06:00
Generally speaking, in most systems, pilot is responsible if he acts with "mens rea" - "guilty mind". That is, basically, if he is aware that he's doing something wrong, or he exercises "willful blindness" by intentionally putting himself in a position where he would be unaware of anything illegal being on board the plane.
Specific bounds of "willful blindness" are somewhat imprecise but it's usually enough to exercise normal standard of care. E.g. a pilot on a scheduled flight is off the hook if he is aware of standard protocols (all passengers and luggage being screened by customs officials before they get on the plane) and nothing hinky is happening. On the other hand, if you're flying a small plane and you have no reason to think that your passengers' bags were properly screened, you have to check for yourself or you may be held culpable.
In some criminal law systems there is a category of crimes that don't require mens rea, that's called "strict liability". This is a much lower bar. For example, you can be found guilty of speeding even if you had no intention to speed and you did not know that you were speeding. All that matters is the fact that you were. However, strict liability is rarely (if ever) used for drug crimes