Possible Clues:

• A spot of moonlighting perhaps for those selling illegal cigarettes
• Novice in back of plane? Seating for those not conscious of duty perhaps!
• Unrecorded and untaxed dealings
• Novice in back of plane? Seating for those going off duty perhaps!
• Does this mean it¿s all tax deductable here for one going off duty
• Refuse to work with restraint in untaxed zone
• Tax-free zone
• A nation's illegally undeclared income