I always understood ( having done the odd trip..or two ) that one of the great "get out" clauses for "management"....was that as a spanner, whilst you could be classed as super nummerary crew for customs docs... but because you were not actually operating crew and the time spent working was, in theory, shorter than the flight time then you were not exceeding your working hours as you could rest.....rest..in a cabin full of Twacy and "well 'ard big Dazzy" pax...??
..or a jump seat of course...on the flight to and from the destinations. Total working hours never
quite seem to be added to the equation.
Sadly of course, there is the perennial problem that engineers always induce...and wonder why they get s£%t on at times....that of overtime as a bait.