Firefly Bob,
I have to go with distance markers as opposed to time markers. My experience is based on remote area navigation over outback Australia. ADF and VOR were sometimes helpful as off-track aids to determine '‘distance from'’ when passing abeam, but I relied exclusively upon time/speed/distance calculations. WAC in this flat country had excellent watercourses marked (probably about one in ten) and although dry were perfectly readable. Watercourses are like fingerprints. When they cross your track, the smallest watercourse will provide distance information and (by reading their unique bends) track information. But I digress.
Ten-mile markers (I was flying C-180’s in those days) provide an easy method of determining both distance and proportion. After some practice one is able to tick the track at ten-mile intervals reasonably accurately without using a scale rule – a handy trick for quick weather diversions. It doesn’t matter if a checkpoint falls between ten-mile markers as it is very easy to estimate the distance down to a mile or so. The markers also serve as a gauge in estimating off-track pinpoints. All my ‘chinagraph’ pencils were notched at ten mile intervals.
Some legs were two or three hundred miles between towns! Several wind changes could occur enroute particularly when passing thunderstorms or through a front. So whilst a WAC with the appropriate markers is essential, an accurate flight log is equally important. Over such distances I found the need to record TAS, HDG, G/S, TMG and determine W/V. Keeping the log was a chore but paid off on a number of occasions, particularly in the winter when overflying solid stratus for a hundred or so miles.
GPS today is a useful tool but should be treated simply as an aid to navigation rather than a definitive solution. Even when flying GPS/NPA approaches one must use other ground based aids to reinforce the decision process and ultimate survival!
Cat Driver & DB6
Surprisingly many Australian instructors have very little experience in remote area navigation (the odd run to Birdsville for the races doesn’t qualify). The experience they pass on is what they too learned from an equally unqualified instructor during their commercial training. It is a pity that instructor pay is so low leading to flight instruction as a stepping stone to that outback job in a Cheiftain. The experienced bush pilots take their knowledge into retirement!