Colleagues (if you will permit me that)
I drive helicopters.
Once upon a time, I was tasked to explore the envelope for night operations in close proximity to cliffs in a Bell 412 (rotor diameter, IIRC, 42 ft). Our minimum clearance was 10 ft, our normal clearance was 15 ft. I spent a day with a tape measure putting markers next to the hangar, and having got a colleague to check independently that my marks were correct, we got airborne in daylight for a first go.
I was really scared getting to 15 ft in daylight, 10 ft was truly horrible. Then we did it again in the dark. Our conclusion was that nobody would ever get that close in an unrecced situation - the pucker factor was far too much - we would have stopped at about 25 ft but for our well-calculated marks.
The point applied to this is that it is near impossible to judge lateral distances in the dark. We could not do it in the 20-40 ft range in a highly controlled situation. AF didn't have a hope.
Sven