The problem here is the VFR routes combined with bad weather. The Victor apron (used by helicopters ) for Atatürk Airport is located in the West. So in any case, regardless of your flight plan, you have to fly away 10 miles to the west, following the VFR routes, not to the North. And that tower is located in the middle of that WEST VFR route with 1100 feet AGL(İmagine a tower on a hill) There is only very small margin of 300-400 feet, taking into consideration that it is not allowed to fly above 1500' for VFR traffics inside İstanbul TMA.So when you combine the route with bad weather, just consider the microclimate conditions occurring over the hills, it's just a bit of perception of crew which were forced to fulfill the job given by.
One last word, it was not the fog, it was the haze together with the rain. This is why the visibility was 4km on the ground but getting worse with climbing.