Thanks, Prospector. "Don't go down until you know where you are" might express things a little too simply. What about "Don't go down to where the ground comes up, until you know where you are". At 20000 feet with cloudbase at 17000 and high ground at 13000, you can go through the hole. At 18000 feet with cloudbase at 10000, you can't, until you've verified your position. If the hole lets you see enough of the ground to do so, fine. But in this case, it didn't. So the decision to descend without the radar fix was an error, in my opinion.