The Right Hand Traffic Rule stated that an aircraft which was flying within the United Kingdom in sight of the ground and following a road, railway, canal or coastline, or any other line of landmarks shall keep such line of landmarks on its left.  For reasons that defeat me the rule went on to give an exception stating, “provided that this rule shall not apply to a helicopter following the Motorway M4 on a route from West Drayton to Osterley Lock!”  Let me take you back to the the birth of commercial aviation in Europe after the First World War.Daimler Airways operated the De Havilland aircraft on the Croydon to Paris route and Grands Express were operating the same route, albeit originating from Paris. The scene was therefore set and, no doubt the astute amongst you will already be speculating on what befell the Daimler Airway mail flight departing Croydon on the 7th of April 1922 and the Grand Express aircraft that left Le Bourget on the same day, just after noon.  This is that story.   The Farman Goliath airliner   The DH18   The BAS 500cc single Gold Star   London to Le Bourget   Le Bourget to London   Traffic in France drove on the right hand side   On that fateful day, the weather was poor   The Picardie accident was the world’s first mid air collision between airliners   Images shown under the Creative Commons licence with thanks to Albert Thuloup, Handley Page, BP, SADSM, The Library of Congress and Popular Mechanics.