BOAC, you are correct regarding GPS problems. We typically lose our reception right after takeoff, and regain it about 3-5 minutes later. The same happens on arrivals.
I have read there are magnetic anomolies, but have not noticed any.
I should have mentioned before that we do not get the VOR/DME R06 approach often, maybe one out of ten arrivals. I did miss this approach about three weeks ago because of no runway in sight at the MAP. The weather was terrible, with CBs, shifting winds, and ice. After the miss, the wind shifted and vectored for the ILS 24.
Cheers,