The use of the Decca flight log is most simply illustrated by referring to an actual flight, in this case on a Viscount service out of London Airport.

Fig. 1, which is a section from the chart roll used on a recent service, shows the London Control Zone chart. Take-off was from runway 2 8 RIGHT on an IFR day and the outward bound clearance was Chertsey 2000 ft., Dunsfold 3000 ft. with a radar climb en route to Seaford. At the time when the pilots are fully occupied with after take-off drills, r.t. &c., and maximum concentration on instrument flying is necessary, a quick glance at the flight log is all that is necessary to check that the aircraft is on track. At this stage, in the event of radar failure, an accurate position of the aircraft can be passed to air traffic control at any time it is requested, and ‘flying well right of the centre line’ and subsequent resumption of track is easily effected.