..........and still, despite the plethora of links - some 'yet to be published', C152 still does not know what to do after setting up a perfect 15nm offset from his/her random track. What an a/c descending through MPNS airspace from above 420 should do should be no different to what an a/c starting at 360 should do, surely? Perhaps you can quote that procedure for the OP from the bedside book? Personally I would weigh the odds against hitting the traffic coming the other way below me exactly on my random track against sailing blithely (offset 15) downwards through several established tracks definitely full of metal. My bedside reading says more important to put myself between and parallel to fixed tracks than to simply fly an immaculate 15nm offset on my random track. My choice, I reckon, since they are my passengers.