In order to meet the "twin-engine" flight standards authorised by the official departments of his company (1hour 45 minutes flight on 1 engine at an air speed of 420 kt to reach the alternate aerodromes in still air conditions), a pilot has to choose an ATC route, in Minimum Navigation Performance Specification area, while at the same time taking the shortest possible time. Given that the three alternate aerodromes taken into account are SHANNON, SANTA MARIA, ST JOHN TORBAY, the track to be chosen between PARIS and WASHINGTON will be: