A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2018 Aug 14, 02:31 -0700
John Howard you wrote: Were the RAF charts you used Tranverse Mercator?
Initially, during training, we used ordinary 1M or 2M Mercators for plotting and ½ M Lamberts topos for calculating safety altitudes and for map reading visually and using radar at low level. As the skies became fuller and more controlled we used en-route charts for high level transit flying, the UK produced ones for Europe and the US ones for North America. Where a route was in common use e.g. Uk to the Middle East they would produce transverse Mercators with, I believe but can't remember for certain, the great circle of contact aligned approximately with the usual route. This meant that you had almost every desired feature of the perfect chart within a couple of hundred miles parallel to the route. We were also trained later to use the Greenwich grid overlay for high latitude flying, but I only ever practised using it around 50N a couple of times, and I can’t remember much about that now. For helicopter flying in the UK and for slow speed light aircraft service training the RAF now uses the 1/4M (M5219) UK Special Air Chart, which is a very colourful, but somewhat cluttered transverse Mercator topo containing both lines of lat & long and also the British National Grid (BNG). I’m not sure what the great circle of contact is, but if it complies with the recommendations of the Davidson Committee of 1935 for future UK maps it should be the 2W meridian. The BNG origin is at 49N 2W, but it is numbered from a false origin located 100kn north and 400km west of the true origin to ensure all UK values remain positive.
Incidentally, Dickie Richardson covered convergency and conversion angle and all its applications in great detail (including how to use a