Polar crossings were certainly not common in the 60's as they simply did not make any sense from a flight planning point of view. I would be very suspect of anyone claiming that they they did polar crossings or even operations above 78 degrees. Yes, we did grid above 72 degrees as I recall?
My log book records London – Anchorage 18th May 1970. My first Polar Crossing.
We flew NNW from London, and for the first few hours the Nav. Instructor would take frequent sun shots with the sextant, and compare the performance of the two compass systems that we had, Captain and Co-Pilot. One of the pre-flight checks was to ensure that we had two meticulously maintained gyros fitted, these were fitted to any aircraft making the Polar transit, the idea being that the maintenance given to these gyros would minimise precession due to friction on the various bearings and “innards”, this would become critical when we switched from magnetic reference to gyro steering.
Gyros maintain their heading in space, theoretically, but precess, i.e. drift off heading, for a variety of reasons, one of them relative to the present Latitude, and our compass controllers had a knob that could set the mid-latitude for the next leg between navigation fixes to correct for the Latitude factor of the total precession observed.
The Nav’s job was to compare the drift of the gyro relative to the Latitude correction that had been set whilst we were still using a North seeking compass function, hopefully zero error if the Latitude correction was accurate, but never say never, and eventually create a graph, similar to a deviation correction chart so that when we switched to gyro steering, not only could he select the next mid-latitude correction, but also apply an additional precession error that he had determined from his Astro observations on the initial part of the flight. Clever stuff, but you small aircraft pilots do apply compass deviation as well as variation to your computed tracks – don’t you, or do you just follow an iPad now ?
Approaching 66 North, the Arctic Circle, compasses were switched to gyro steering, and a Grid heading flown, determined from a polar chart with a Mercator type grid superimposed. If for instance the heading was determined as 330 deg Grid, this could be plotted on the chart and flown beyond the Pole, when one would actually be flying South by normal consciousness.
We actually flew between the True North Pole and the Magnetic North Pole, and apart from the fact that a magnetic compass was useless in that region, the rapidly changing angle between required track and the local Longitude was changing far too quickly to compute with the human brain and an E6B wind drift computer. Remember, this was before even Inertial systems, never mind GPS and iPads.
Where it all got a bit mind blowing was when Fairbanks VOR started to be received, one could be – for example – on the 020 (M) radial of the VOR heading towards it, but the Grid heading being flown might be 340 (G), i.e. one appeared to be flying North, but in reality was now flying South, and the VOR needle would be pointing behind the aircraft tho’ in reality one was flying towards it.
Please don’t pick me up on the nitty gritty of all this, it is 40+ years since I last did it, just think about it !
ExSp33db1rd.
Now's the time, please!
The cheese story ... leaving London one had many hours to sort all this stuff out, but out of Anchorage on the return sector one was thrown almost instantaneously into the Polar navigation exercise. I recall the “Grivation” i.e. a mix of Grid angle of the chart relative to True North, and the local Variation, was in the order of 174 deg east as we left Anchorage, which meant that if one applied it in the wrong direction – never say never – one could set off towards Siberia instead of Europe, very embarrassing. I used to calculate the Grid heading required, then give the available data to the co-pilot, and ask him to calculate it too, and if we agreed within a degree or two, then we would switch the compasses to Gyro and set off.
Company rules said that if there was any doubt as to the accuracy of the gyro compasses, then turn back. One Captain suspected such an error, but called for the cheese tray, cut off two lumps and balanced them on the windscreen coming and stuck a toothpick in each such that the shadow of one fell across the other, i.e. a sun position line.
Then he told the navigator to use the sextant to determine the True heading, and the consequent Grid heading to steer, turned the aircraft on to this new heading and re-arranged his cheese. Then he maintained that sun line for 20 minutes and repeated the exercise. He kept this up for about 2 hours until they were back into an area of normal compass operation, when they decided that in fact it was the co-pilots gyro which had been dodgy. I don’t think that they ate the cheese at that point.
When the stuff hit the fan because he hadn’t turned back, he said – the sun moves at 15 deg. an hour, by steering a constant bearing for 20 minutes, the most I could have been off the required heading was 5 deg. and that only at the end of the 20 minutes, as well. When we thought we had a problem we knew where we were, we knew where we were going, had we turned around and tried to re-establish ourselves back to Anchorage, we’d have been f***ed.
That Captain had been an RAF Coastal Command skipper in WWII, and they all had to be proficient on navigation as well as flying. I understand the theory but I doubt that I would have had the courage, and I’m glad that when I was a Captain I had the benefit of triple INS
Happy Days.