A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2021 Mar 15, 03:17 -0700
David C You wrote: Can someone explain the meaning of "running down a position line". To me ...........
David. I think the problem in my, and probably many others, case was that I was confused because of my familiarity with later electronic navigation aids. With GEE, Decca, and ILS localiser, you really did/do run down a position line. You aligned signals and made left/right adjustments to course to ensure the signals remained aligned. The difference between modern aids and celestial is that whereas great pains were/are taken to ensure GEE, Decca, and the ILS localiser beams remained/remains in exactly the same place 24/7, celestial lines have the annoying habit of wanting to move west all the time.
Therefore, Sumner’s, if he ever used the term, and Chichester’s meaning of ‘running down a position line’ is far more basic than that. In Chichester’s case, I’m beginning to think he was just putting himself into the best possible position from which to start his final 40-minute leg. He also claims on pages 29/30 of The Observer’s Book Part 4 that he was able to tell if he was flying towards or away from his objective by taking another Sun shot 20 minutes later. I’m still checking to see if that would work for all parts of the world, tracks, and times of day or only over the Tasman sea in the afternoon. From what I can see, Chichester certainly wasn’t able to make and didn’t try to make constant tracking and distance checks once he was established on his final leg. He was more like likely, as Lindberg advocated, to have concentrated upon flying his chosen heading very accurately.
So yes, Chichester used his 0500 GMT LOP, which was slightly more across than parallel to track to calculate that he should turn onto his final leg at 0515GMT. Wherever he’d been along that 0500 LOP, by turning at 0515 he was nevertheless turning onto his final leg although his exact distance from Lord Howe Is. was by no means certain. Once established on final heading, the Sun was close to abeam and was ideally placed for a tracking check at 05.20. I think this is the main point of what he means by the value of ‘running down a position line’. He appears to have taken no more Sun shots after that. Hence the need for flying an accurate heading and maintaining a good lookout. A lot of journalistic accounts gloss over the full details, so you have to go around several of the more navigationally complete sources until the full picture becomes clear in your mind, or perhaps I’m a bit dim. DaveP